Smell Life

Scent of a Woman

Rachel Herz, Ph.D. — Sat, 13 Mar 2010 18:49:14 +0000

Above and beyond looks and bank account size, women rank how a man smells as the number one determinant for whether she'll be sexually attracted to him. Moreover, what men each woman finds most sexy smelling varies widely and is tied to immune system genetics. Everyone (except identical twins) has a genetically unique immune system, and the specific genetic fingerprint of your immune system is outwardly represented by your body odor. Research shows that naturally cycling women prefer the body-odor of men whose immune system genes are relatively different from their own. This "opposites attract" phenomenon is what evolutionary matchmaking aims for, as it is adaptive for fecundity, infant survival and reproductive success.

When it comes to men, the story has been that how a woman looks-her hourglass figure, full lips, lustrous hair and sparkling eyes are what appeal most. This is not superficial or sexist; it makes good evolutionary sense because these physical attributes are in fact signals to youth and health and therefore probabilistic fertility. By contrast, though a few studies have shown that men find a woman's natural body-odor to be most pleasant when she's ovulating, there has been little else to suggest that a man's biology is at all influenced by scent. However, other male mammals use odor as the dominant cue for the initiation of sexual behavior. A male rhesus monkey with a blocked nose will ignore a female in heat. Now new research from Florida State University has revealed that human males may be driven more by the scent of a woman's "heat" than has ever been realized before.

Saul Miller and Jon Manner tested college men for their responses to T-shirts that had been (1) worn to bed by college women who were ovulating, or (2) worn to bed by college women who were not ovulating, or (3)T-shirts that hadn't been worn by anyone (unscented). Regardless of the condition, all men were told that the shirts "had been worn by a woman" and they were asked to take big sniffs of it three times over a 15 minute session. Testosterone levels were measured before they sniffed and then after the 15 minute T-shirt session. Testosterone, the male sex hormone, is directly influenced by external cues- when heterosexual men interact with an attractive woman or watch pornography their testosterone levels rise.

Miller and Mann's study revealed that the men who sniffed T-shirts from ovulating women had higher testosterone levels than the men who sniffed T-shirts that didn't indicate fertility; either worn by non-ovulating women or unworn. But the testosterone levels of the men who smelled the shirts signaling fertility didn't actually increase from their pre-sniff levels, as happens when men are exposed to other overt sexual signals. They just didn't drop-- which is what happened to the men in the other conditions-- who sniffed T-shirts that didn't indicate fertility. There are various possible explanations for this finding. My speculation is that it reflects the biological response to either a thwarted or successful sexual ‘match to expectation'.

If you tell a heterosexual man that he's going to be smelling a T-shirt from a young woman, evolutionary theory might suggest that he would become interested both mentally and physiologically-- as a possible indication of mating to follow. However, if the actual act of sniffing does not in fact signal the "presence" of a woman with immediate reproductive value (as in the case of T-shirts from non-ovulating women or not worn), this unconscious biological disappointment may manifest as a drop in testosterone. By contrast, the constant level of testosterone observed in the men who smelled T-shirts from ovulating women may indicate a match to expectation. In order to test whether this explanation has any merit we would need to know what the level of testosterone was in the men before they were told anything about the T-shirts. Or we might conduct a new study where men are given various types of reproductive information (false or not) about the women whose T-shirts they may be smelling. It would also be fascinating to know whether any testosterone changes occur when heterosexual men smell T-shirts worn by other men (under various "informational" conditions). I could go on. Suffice it to say that this is a fertile field for future research!

Citation:
Miller, S. L. & Mann J. K. (2010). Scent of a woman: Men's testosterone responses to olfactory
ovulation cues. Psychological Science, 21, 276-283.

Rachel Herz is the author of The Scent of Desire and on the faculty at Brown University.
For more information, click: Rachel Herz

Aromatherapy for the Holidays

Rachel Herz, Ph.D. — Wed, 09 Dec 2009 20:01:59 +0000

Shopping, blizzards, school cancellations, cooking, parties, relatives, work. December brings a storm of activities and situations that combine to create the possibility for a great deal of fun or madness. Somewhere in between is the edginess and breathlessness that most of us feel for at least a day or two this month. What can you do to relieve the stress? Yoga and exercise are great if you have the time, but something that doesn't require any of your time is using your nose. Lavender and orange citrus scents have both been scientifically validated to produce relaxation, enhance sleep quality, increase positive mood and reduce tension during stressful situations. These scents are cheap and easy to find, and just a momentary whiff can be enough to turn down your emotional temperature and slow your heart rate. Sound like magic? Well it's not.

Scents are not magic potions or drugs. If a scent affects your mood and physical state it is because of the emotional association you have to it, and the physiological consequences that emotional state induces. Feeling relaxed slows your heart-rate, feeling excited quickens it. If lavender creates the feeling of calm for you it's because you have experienced deep calm while exposed to lavender in your past. You may have been getting a gentle message and your message therapist was using lavender oil, or you may have been soaking in a warm tub with lavender scented soap, or something else personally comforting. Experimentally, the scent of lavender has been found to make people feel more relaxed and sleep better. Similar outcomes have been found for orange-citrus aromas. Experiments have even shown that a citrus orange scent is better than mood music at making people feel happier and less tense during a stressful situation. The reason why scent is so good at inducing mood is because olfaction has a more direct and immediate connection to the area of the brain that processes emotion than any other sense does.

Since the effects of aromas are due to our own personal past history with the scents in question, they can be idiosyncratic. If you don't like the smell of lavender or orange then you aren't going to feel relaxed after smelling them; you may even feel annoyed. And, if you've never smelled lavender or orange before you won't be soothed by them either. What's more, if you're exposed to a scent such as lavender, but are led to believe that you're smelling something else, with for example, invigorating qualities, lavender aroma won't relax you and in fact may make your heart-rate jump. This underscores how psychologically susceptible our experience of scent is.
An orange scented candle or a bar of lavender soap may be just what you need for a reviving and relieving time-out during the holidays. But the most important point is to find a scent that makes you feel good, and any scent will do. The remnant of fragrance in an old perfume bottle, the smell of a loved one's sweater, the aroma of macaroni and cheese dinner, or the scent of a special flower-- if it makes you feel comforted then it can be your aromatherapy for the holidays and beyond.

One cautionary word, don't use your therapist in a bottle too frequently. If you continuously expose yourself to a scent you will adapt to its aroma and not be able to smell it. And if you can't smell it, a scent can't help you.

Rachel Herz is the author of The Scent of Desire and on the faculty at Brown University.
For more information, click: Rachel Herz

Illegal Odors

Rachel Herz, Ph.D. — Tue, 20 Oct 2009 16:32:52 +0000

I recently read that Honolulu is seeking to criminalize "being too smelly" on public transit. According to an article posted by the Associated Press on September 2, 2009, two city councilmen have co-sponsored an anti-odor bill that would impose a $500 fine or up to six months in prison to any bus rider convicted of failing the sniff test. The specific criteria of this sniff test are: "odors that unreasonably disturb others or interfere with their use of the transit system." Moreover, these so-defined scents could be anything deemed emanating from the individual and/or his possessions.

This law if enacted would be the first criminalization of personal odor in the United States. The city of Halifax in Nova Scotia imposed a ban on scent in 2000, specifically artificial scent, which resulted in elderly ladies being kicked off buses for wearing perfume and high school students being accused of "assault" for sporting hair gel and Aqua Velva in class. I have not found confirmation that anyone has ever been jailed or fined for these Canadian scent offenses.

The Haligonian by-law was enacted as an appeasement to people suffering from Multiple Chemical Sensitivities. This is a condition, which Halagonians apparently suffer from in large numbers, as over a two year period around the time this law was imposed nearly 800 people presented to their doctors with the experience of a cornucopia of allergic reactions to odors, especially "artificial" ones (1). The difference between this situation and the one which Hawaii's capital is attempting to enforce, however, is that the latter is based solely on personal opinion and hence prejudice.

What makes an odor smell bad, or good, to anyone is highly dependent on the personal history of the perceiver. If someone has a negative association with the scent of roses, it will be a bad smell for him and likewise if someone has had a positive encounter with the smell of skunk it will be a pleasant scent for her. However, the context in which one is sniffing the scent plays an enormous role. The scent of skunk wafting across a meadow would be highly pleasant to me, but if it came out of my shampoo bottle I would surely be disgusted.

The person producing the odor is as much a context as a container or scenery. The bedraggled bus rider, who hasn't showered in two days, is much more likely to be perceived as emitting "disturbing odors" than the well healed business man, even if the business man hasn't changed his suit in a week. What's even more disturbing is that this bill evokes our own unfortunate racist past. In 1937 the psychologist John Dollard, while studying the development of race relations in the South, observed:
"Among beliefs which profess to show that Negro and white people cannot intimately participate in the same civilization is the perennial one that Negroes have a smell extremely disagreeable to white people."(2)

The color of the bus-rider's skin may therefore be enough to elicit a "disturbed" reaction from fellow riders, as may the rider's foreignness. Jacques Chirac, the former prime minister of France, openly declared his sympathy with the French worker for "having to put up with the noise and smell of the immigrant family living off welfare next door." The foreignness of smell along with the foreignness of the "other" goes deeply towards ingraining ethnic denigration and xenophobia.

Fortunately, the American Civil Liberties Union of Hawaii has recognized the potential for prejudicial discrimination that this bill may provoke. I sincerely hope that they are able to lobby successfully against the anti-odor bill's enforcement.

(1) The disease process of this condition has not been substantiated.
(2) Dollard, J. (1937). Caste and class in a Southern town. New York: Anchor Books.

Rachel Herz is the author of The Scent of Desire and on the faculty at Brown University.

For more information, click: Rachel Herz

The Truth About Pheromones: Part 2

Rachel Herz, Ph.D. — Thu, 18 Jun 2009 19:28:21 +0000

Pheromones come in two forms: "primer pheromones" that cause slow, long-term physiological changes such, as hormonal effects; and "releaser" (or signaling) pheromones that produce rapid behavioral effects, such as mating. Pheromones are not cognitively processed chemical signals, but rather elicit instinctive and presumably unconscious responses. Moreover, pheromones typically do not have a scent per se and are often in a liquid medium. As such, in mammals, including primates, which use pheromonal communication they are processed through a non-scent organ system, the VNO and accessory olfactory bulb. We don't have this physiological hardware and in my last posting I left you hanging with the question of whether we can respond to and use pheromonal communication. These are two possible answers: (1) No or (2) Yes. And if the answer is "Yes", how do we do it?

The best demonstration of a human pheromone is the "McClintock Effect": the coincidence that women who live together seem to get their periods at the same time of the month. It is known as the McClintock Effect after Martha McClintock's observation that girls in the same dormitory began cycling in synchrony over a college semester. Since her first observations numerous experiments have demonstrated that applying the sweat from one woman to the skin above the upper lip (i.e., under the nose) of other women is capable of altering the others' menstrual cycles to be in synch with the donor woman¹. This is an example of a primer pheromone-- a physiological change that occurs over time. There is good evidence for the McClintock Effect as many experiments have replicated the finding, but it has also been criticized as simply due to statistical artifact. The hormonal changes that take place over the approximately 28 days of the human menstrual cycle are graphically depicted as a wave. It is mathematically the case that waves with different cycles will come into synch with each other over time and then drift apart². Therefore, the menstrual synchrony effect could be nothing more than the product of mathematics and the fact that it is much more interesting to notice a coincidence than the lack of one. Nevertheless, if we accept the McClintock Effect as a true human pheromone, how do women respond to it if we are missing the organ-system for detection?

One explanation is that the chemicals responsible for inducing menstrual synchrony are transmitted through the skin. The sweat from one woman is absorbed through the skin (e.g., above the lip) of the woman who receives it and over time enters her bloodstream causing changes to her hormonal system. In a naturalistic setting this could be quite plausible too. Women who live together touch the same items and each other all the time-- borrowing clothing, picking up a book or mug, and touching hands to exchange items-- and therefore are likely swapping sweat on a regular basis. An alternative explanation is that the chemicals responsible for the McClintock Effect are actually processed through the olfactory system, and that in both experimental and naturalistic settings smelling the donor woman's sweat is the key to changing the other women's menstrual cycles.

The main compounds that give our underarm odor its bouquet are carbon chain acids, but there are other chemicals present too, in particular one that has recently received a lot of press-- androstadienone. Androstadienone is a steroid and a derivative of testosterone. It is also found in higher levels in male than in female sweat. These features make it an intriguing candidate as a possible human sex pheromone.

Two recent studies have provided suggestive evidence that this may be the case. One study tested whether there were changes to a woman's mood when she was exposed to androstadienone or a control solution in the presence of a male or female experimenter. When the female experimenter was present, androstadienone had no effect, but in the presence of the male experimenter androstadienone increased women's positive mood and decreased negative mood factors³. The control solution had no impact on mood regardless of the experimenter. Another study with only a male experimenter found that sniffing androstadienone increased women's self-rated mood, sexual and physiological arousal, and even affected secretion of the hormone, cortisol⁴. These results have led to the speculation that androstadienone is a "modulator" pheromone for women in certain social contexts-the presence of men. However, it is possible that the specific male experimenters in these studies had an influence on the women's responses, and until more research is done on the "male context effect" conclusions remain tentative. Furthermore, the level of androstadienone that women were exposed to in these studies was a million times higher than the amount a normal male emits. Thus, the ecological validity of androstadienone as a naturally active human pheromone is questionable. Nevertheless, it is tempting to contemplate that high levels of androstadienone worn by men could sexually modulate women's mood and physiology.

Men, it seems, may also be affected by sweat based chemicals. In a recent experiment, Geoffrey Miller and his colleagues found that professional exotic lap dancers earned almost twice as much in tips (averaging $335/night) when they performed during the ovulatory phase of their cycle compared to the menstrual phase of their cycle (averaging $185/night)⁵. But the dancers all claimed that they performed the same way every day and that their behavior to the patrons was always consistent. So were the men responding to some chemical sex signal emitted by the dancers when they were fertile?

There were no independent assessments of the dancers performances over their cycles, and therefore it is not known whether they truly did perform without variation from day to day. Female libido is known to be higher during ovulation, as is moodiness and physical discomfort during menstruation. Therefore, the dancers may not have realized that they behaved more sensually during fertile days and less so while menstruating. Moreover, what the male patrons were responding to-the dancers' scent, looks, moves or demeanor-- is not known. So the cause of this provocative finding is still a mystery.

Much more work awaits to be done on men and women as recipients of each other's chemical signals and so for now I leave you to decide. Will the aromachemical industry find and bottle a sure-fire human pheromone for sexual arousal? Or will we need to rely on how our conscious noses respond to each of our unique and fragrant bodies to tell us whom we desire?

1. McClintock, M.K. (1971). Menstrual synchrony and suppression. Nature, 229, 244-245.
2. Wilson, H. C. (1992). A critical review of menstrual synchrony research. Psychoneuroendocrinology, 17, 565-591.
3. Lundstrom, J.N. & Olsson, M.J., (2005). Subthreshold amounts of a social odorant affect mood, but not behavior, in heterosexual women when tested by a male, but not a female experimenter. Biological Psychology, 60, 197-204.
4. Wyert, C. et al. (2007). Smelling a single component of male swat alters levels of cortisol in women. The Journal of Neuroscience, 27, 1261-1265.
5. Miller, G. et al. (2007). Ovulatory cycle effects on tip earnings by lap dancers: economic evidence for human estrus? Evolution and Human Behavior, 28, 375-381.

Rachel Herz is the author of The Scent of Desire and on the faculty at Brown University.

For more information, click: Rachel Herz

The Truth About Pheromones: Part 1

Rachel Herz, Ph.D. — Mon, 18 May 2009 16:14:09 +0000

The tank tops are on, the shorts are tight, the skirts and short... summer's coming and we're baring our bods in hopes of snaring some fun summer love or more. Not only are we looking at each others biceps, thighs, chests and faces, we "sense" each other too-with our noses. What are our noses telling us? In addition to pure body-odor and fragrant applications is there something more our nasal passages and the secret recesses of our selves are responding to? Is this the chemical attraction that everyone's calling "pheromones"?

The topic of pheromones needs some explanation, so I'm going to start by giving you an overview of what pheromones are. The word "pheromone" was coined in 1959 by Peter Karlson, a German biochemist, and Martin Lüscher, a Swiss entomologist. It is derived from the Greek, pherein meaning "to carry" and hormon meaning "to excite"- in other words "carrier of excitement." Karlson and Luscher used this word to describe what they were witnessing in their insect lab-that a chemical substance released by one insect-in their case termites, seemed to affect the behavior of other termites around it. They coined the word "pheromone" to describe the general phenomenon that a chemical released by one animal could affect the physiology or behavior of other animals of within its species. Simply put, pheromones are chemical communication, and they are highly important for animals, like the social insects who use chemical signals as their primary mode of communication.

Pheromones also convey important information for many non-insect species, including primates. The reason for the bawdy connotation of "pheromone" in our modern parlance is because for mammals, one of the most important forms of messages they carry are communiqués about reproductive status and availability. For example, androstenone, a pig pheromone, turns a sow's attention to mating and nothing else, and induces her to assume the sexually ready position. This automatic reaction has been exploited by pig farmers wishing to spare the expense of keeping male studs. There is a commercially available spray of androstenone called "Boar-Mate" that given to a sow, eases the process of artificial insemination. A male rhesus monkey will even ignore an amorous female in heat if he can not detect the pheromones that signal her fertility. The fact that other mammals produce and react to pheromones which play an indispensible role in their sex lives is why people in the fragrance industry hold out hope for a human sex pheromone. If such a chemical aphrodisiac could be discovered and bottled it would be the biggest thing in history of cosmetics and fragrance.

Because many pheromones involve chemical secretions that are "smelled," or have a smell, this has led to the erroneous conclusion that pheromones are odors, which they are not. Pheromones are chemicals which may or may not be smelled at all. It is also the case that pheromones are not normally picked up and processed by the olfactory system, but rather by a separate structure called the vomeronasal organ (VNO) which connects to the accessory olfactory bulb, an independent structure from the main olfactory system. The VNO is located above the roof of the mouth and evolved to detect large molecules and molecules that are dissolved in liquid, which is why licking various body parts-as dogs do when they great each other-- is a key way for pheromonal information to be received. We can only "smell" with our nose small airborne molecules.

All animals that have been documented to use pheromonal communication use their VNO for detecting them. One major problem for creating our billion dollar pheromonal potion is that we do not have a functioning VNO. Human embryos may have a VNO, but after birth this tissue disappears. There continues to be controversy surrounding this issue, but overwhelming evidence points to there being no functioning neural tissue in humans that corresponds to the VNO of other animals. Moreover, although it may be possible for the main olfactory bulb to process pheromones, the accessory olfactory bulb to which VNO nerves normally project, has not been found in humans. So what does this mean for us and pheromones? Stay tuned for next time...!

Rachel Herz is the author of The Scent of Desire and on the faculty at Brown University.

For more information, click: Rachel Herz

Fragrant Attraction

Rachel Herz, Ph.D. — Thu, 19 Mar 2009 17:15:15 +0000

Many people, including mavens in the fragrance industry, believe that aromatic aphrodisiacs exist, and are only waiting to be found. The competition in the commercial world for this holy grail is fierce because if such a magical elixir could be captured it would be the beginning of a trillion dollar industry, not to mention the solution to loneliness and guaranteed success for nights out on the prowl. Type the word "pheromone" into Google and you'll get hundreds of hits for companies offering to sell you wearable pheromones "guaranteed for sexual success", along with various merchants purporting "data" that their elixirs boost the sex life of those wearing it. But think for a minute about how we might also interpret data that wearing these potions makes those donning them more sexually successful.

The marketers of Wonder Bra in Canada used a wonderful truism in an ad jingle of the 1970's; "if you look good you feel good, and if you feel good you look great." If you believe that by putting something on-whatever it might be-it will make you more attractive to the opposite sex, your behavior will change. You'll feel more confident and secure and you'll be more flirtatious and happy-which will increase your attractiveness to others and thereby boost your sex life. None of this has anything to do with mysterious pheromones, rather it has all to do with self-confidence.

Indeed in a recent study conducted in the UK, men who wore the British label version of AXE deodorant (Lynx) were rated by woman as significantly more attractive than men who weren't wearing scented deodorant (1). The surprise, however, is that the women didn't actually smell the men-the men just smelled themselves. Women rated headshots of 35 men and 15 second video clips of the same men imagining introducing themselves to an attractive woman. The women rated all the men as equally attractive on the basis of their photos. But on video, the men wearing scented deodorant were rated as significantly more appealing than the men who weren't wearing fragrance, and the women only watched the video clips for 15 seconds. Probing why the AXE men were so much more alluring the researchers found that it had to do with how confident the men felt and how the scent of the deodorant made them feel. The more the men liked the fragrance they were wearing, the more confident they felt-- and the more confident they felt the more attractive their body language was to women. The other amazing finding was that it only took 15 minutes of wearing the scented deodorant to boost the guys' self-confidence. On the opposite side of the aisle, in a large survey study I found that 90% of women (from teenagers to seniors) feel more confident when wearing fragrance than without (2). Therefore wearing a fragrance you like will make you feel better about yourself which will consequently make you more attractive to others.

However, there is biological peril, especially for women, to the magic of fragrance. Not only does a man's use of fragrance make him behave more charmingly, my laboratory has shown that above all other physical characteristics, women rank how a man smells as the most important feature for determining whether she will be sexually attracted to him. Critically, she doesn't discriminate much between whether his scent comes from his clean natural body-odor or from the bottle on his dresser. The reason this is a biological hazard is because, as my last blog explained, our body-odor is the representation of our immune system genes and women use their noses to choose their "correct" biological mate to ensure maximum fertility and child health (see The Scent of Sex ). Therefore by wearing a fragrance that a woman finds enchanting, a biologically unsuitable man can trick a woman into being with him by "falsely" smelling scrumptious.

The take home message for men is: if you smell good to yourself and to the lady of your dreams you'll be a sure-fire winner. But for women the message is: beware a man who smells too good because of his fragrance. If you think he has potential and you're on the hunt for a man to be your mate, ask him to wash with unscented soap and to kick the fragrance/deodorant habit for a while. If your nose and heart remain enamored then you're on to something good.

(1) Roberts, S.C., Little, A.C., Lyndon, A., Roberts, J., Havlicek, J. & Wright, R.I. (2009). Manipulation of body odour alters men's self-confidence and judgments of their visual attractiveness by women. International Journal of Cosmetic Science, 31, 47-54.

(2) http://www.senseofsmell.org/research_exchange/finalreports.php

Rachel Herz is the author of The Scent of Desire and on the faculty at Brown University.

For more information, click: Rachel Herz

The Scent of Sex

Rachel Herz, Ph.D. — Tue, 03 Feb 2009 18:55:17 +0000

This is the month when we turn our hearts and minds to love. February 14, our calendar's date for romance, became connected with St. Valentine in the high middle ages, and has evolved to be celebrated with love notes, mass consumption of chocolate, and first or special dates. Valentine's Day was originally marked by a mutual exchange of love notes between men and women, but the US Greeting Card Association estimates that today 85% of Valentine's are bought by women. The fact that women do the majority of the "sending" to their would-be or current lovers reflects the biological orientation of our species-- women are the choosers of their suitors.

A number of surveys examining how we rate the appeal of the opposite sex, have found that men place the highest importance on how physically attractive a woman is, while women find men of high status, power, resources and money most attractive. The contrast of "looks" with "status" between men and women makes evolutionary sense. Physical attractiveness in women is indicative of potential fertility and social status in men is indicative of being able to help a woman rear her children.

Though a warm house, hired help, and plenty of nutritious food will certainly support a woman's ability to raise a child, the most important factor in the evolutionary game is that the child herself be healthy enough to thrive and be reproductively successful. So for women, finding a man who can provide material benefits is good, but most importantly he should be able to sire physically healthy children. But what determines whether a particular man can produce healthy children? The answer lies in his immune system.

Our immune system determines what diseases we can defend against and how well, and what diseases we may carry as recessive traits. But even more important than the general robustness of a man's immune system is the complementarity of his immune system with the immune system of the particular woman he is having sex with. That is, how the number of possible pathogens the two of you can fight against and how unlikely you are to double up on nasty recessive disease traits measure up. So the goal for a woman is to find a healthy man who has a different immune system from her own. But how can a woman tell what a man's immune system is like?

Our immune systems are coded for by a cluster of genes called the major histocompatibilty complex (MHC), and everyone, except if you have an identical twin, has a unique set of MHC genes. Your unique string of MHC genes are the genotype for your immune system, and your phenotype, the external manifestation of the genes for your immune system, is your body-odor! And your odorprint is as unique as your fingerprint.

In the now famous "T-shirt" experiments it was shown that specific women chose as most sexy and pleasant smelling T-shirts belonging to men who had immune systems that were different from their own. Because we all possess different MHC genes (and body-odor), for every woman a different set of men will be delicious smelling and others won't be. There's no Brad Pitt of body odor! A woman's nose not only responds to a man's body-odor in terms of his biological suitability, women actually find how a man smells to be the most important factor in their sexual attraction.

In two large studies we conducted to examine how important various physical and social status factors were for men and women when choosing a sexual partner, we discovered that above all other physical characteristics, women ranked a man's scent as the most important feature for determining whether she would be sexually interested in him.* How a man smelled was also more much important than any social status factor. And of all physical characteristics women preferred a man to be "better than average" in his body-odor than anything else. Women also found men who smelled great due to the fragrance they wore irresistible. In the words of one respondent: "If I'm with a guy who smells really good, nothing else about him seems to matter." So listen up men, it's real chemistry between you and your love interest and her nose is going to decide whether she'll let you be her Valentine tonight.

*Men found how a woman looked to be the most important factor. For more information see references below.
Herz, R.S. & Cahill, E. D. (1997). Differential use of sensory information in sexual behavior as a function of gender. Human Nature, 8, 275-286.
Herz, R.S., & Inzlicht, M. (2002). Gender differences in response to physical and social signals involved in human mate selection: The importance of smell for women. Evolution and Human Behavior, 23, 359-364.

Rachel Herz is the author of The Scent of Desire and on the faculty at Brown University.

For more information, click: Rachel Herz

Smell Your Way Thin?

Rachel Herz, Ph.D. — Mon, 05 Jan 2009 18:11:41 +0000

If you're like me then you're currently preoccupied with getting rid of the evidence of the past weeks' excesses that's hanging over your waist band. Your appetite and penchant for high-fat treats seems to have grown-who wants to eat an orange when there's turtle cheesecake in the fridge?! And what are you supposed to do with the boxes of chocolates your evil friends gave you? Not to mention you're trying to maintain a festive mood-just last night you went out for burritos and margaritas with your friends and tomorrow you're going out again. Maybe you'll get that nasty stomach bug that's going around....? No you can't think that, you know what kind of bad karma it is to wish illness upon yourself.

Kaynahorah to the evil eye for a moment and I'll tell you that if you were to get that stomach bug after last night's feast of burritos, in addition to dropping a few pounds you'd be easily able to resist Mexican savors for quite a while to come. The reason is due to the phenomenon of "learned taste aversion", being sick to your stomach after consuming a distinctively scented/flavored food will make you steer clear of the scent of that food for a long time to come. This instant form of smell conditioning is highly adaptive. Food consumption and gastric distress are physiologically linked and even if there is no true causal connection between last night's burritos and your stomach flu, we are wired to immediately learn to avoid the scent involved in that consumption connection. We wouldn't survive long if we were continually poisoning ourselves on the same deadly mushrooms.

Conditioning is also at the root of one way to stay the temptation of fattening delights. In a study done at St George's Hospital in London in 2000 researchers found that dieters who wore a vanilla scented patch, compared to a lemon patch or no patch, lost more weight. The reason they lost more weight than the other dieters was because their cravings for sweet foods were reduced. The sweet aroma of vanilla was able to satisfy their desire for pastries and chocolates and so they were less likely to get their hands caught in the cookie jar.

Vanilla smells sweet because it is always experienced in conjunction with sweet taste and sweet tastes are inherently pleasurable. Put a drop of sugar on a newborn's tongue and you'll see her smile. Sweetness is a hardwired signal for carbohydrates and carbohydrates are necessary for our survival. Moreover, from early childhood on we are given sweets as treats and rewards, both of which are powerful happy elicitors. Thus through our conditioning history of vanilla scent with the positive force of sweetness, we can get a pleasure hit from its aroma without the calories. But this only works if you aren't hungry. There is considerable evidence that food aromas stimulate our appetite even if we're only mildly peckish. Cinnabon kiosks that pump out their hypnotically enticing aroma are preying on just that state. And beware claims that the scents of green apple or peppermint will make you shed pounds. There is no experimental data to support these outcomes and it doesn't make sense from either a conditioning or physiological perspective that these aromas would have any effect.

If you've just had a satisfying low calorie lunch, and you're someone whose sins err on the side of cupcakes, sniffing vanilla can truly help you from dipping into the donuts at work. But if you're more drawn to burritos and french fries you're out of luck. Although sniffing your favorite savory snacks might help quell a momentary urge it is unlikely to be as effective as vanilla aroma because the inherent pleasure hit from savory is less direct and powerful than for sweet. So for me and others who are more seduced by nachos than cookies, good old fashioned exercise and restraint are going to have to be the method on order. Declarations of good intentions help, so after I go for my run, I will eat an apple rather than explore an unopened box of chocolates. And after my dinner tonight of salad niçoise I will sniff some sweet vanilla and leave that cheesecake alone.

Rachel Herz is the author of The Scent of Desire and on the faculty at Brown University.

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Making Scents of the Holidays

Rachel Herz, Ph.D. — Fri, 05 Dec 2008 18:49:35 +0000

Our experience of the holidays just wouldn't be the same without our noses-in fact it would be sadly bland, and I'm not just talking about food. The scents that emanate from certain dishes, certain plants, certain candles and a host of other specific holiday items are intimately tied to our emotions and our past.

Imagine yourself in the following scene: You walk into the warmly lit parlor and before you turn the corner to see the ever-familiar parental living room, you inhale and wafts of fire-place smoke, pine needles, sugary cinnamon, and roasted turkey all mingle together in your nose. You feel heady and happy, like a child again, and with a blend of elation and nostalgia turn the corner to see the holiday scene unfold as you knew it would. But what if all you could do is see this scene without the feelings that the aromas brought with it? Your holiday homecomings would probably be strangely empty.

Why are scents so deeply connected to our emotions and nostalgia? The answer lies in the unique connection between the sense of smell, our brain and our biology.

The chemical profile of an odor is first detected by neurons in your nose. The signals then travel to the brain where they are decoded by two blueberry sized structures-- the olfactory bulbs. From the olfactory bulbs, an odor's signature is sent to other parts of the brain. First and foremost to the limbic system, where associative-learning and our basic drives comes from and most importantly where our ability to experience emotion originates-- a structure in the limbic system called the amygdala. When the amygdala is activated we experience emotion, and when the amygdala has been damaged our ability to process and remember emotional information is lost. In my recent experiments on scent-evoked memory using neuroimaging techniques, I found that when participants recalled a significant personal memory to the smell of a special perfume, the amygdala was much more activated than when they recalled the same memory to the sight of the perfume bottle. None of our other senses have this direct and intimate connection with the areas of the brain that process emotion, associative learning and memory.

In addition to the distinctive neuroanatomical connection between our sense of smell and emotion, there is evolutionary evidence that the perception of smell was linked with emotional experience early on. The structures of the limbic system evolved from tissue that was originally dedicated to odor processing. In other words, the ability to experience and express emotion grew directly out of the brain's ability to process smell. I have often wondered whether we would have emotions if we did not have a sense of smell; I smell therefore I feel?

The feelings that holiday scents evoke have special meaning to us because of our personal associations with them. There is nothing inherently pleasing or nostalgic about the fragrance of pine needles, cinnamon, or sugar cookies. It all has to do with our past personal connections to them. Holiday scents are typically culturally determined but your personal ones may have nothing to do with North American traditions, and they could also be unique to you. If you come from somewhere where a wintry festival of lights doesn't exist then the scents of your holiday could be hibiscus blossoms or curry powder. Moreover, holiday scents don't necessarily make you feel joyous. If you are someone with unhappy memories of Christmas past then the scents connected to this day are going to make you feel bad, not good.

Scents have a singularly potent ability to instantly transport our hearts and mind to times gone by, but only if you have a history with that scent, and a scent can only transport you to your personal past, not a Hallmark ideal. Hopefully there are some aromas connected to your holidays that bring a special smile to your face, and if you can't wait until Christmas, Chanukah or Kwanzaa to experience them, go and get that special scent treat now for your own personal rush down memory lane.

Rachel Herz is the author of The Scent of Desire and on the faculty at Brown University.

Comfort Smelling

Rachel Herz, Ph.D. — Thu, 06 Nov 2008 17:09:11 +0000

Have you ever had to cancel a dinner date or miss an important meeting because your toddler pitched such a fit when you tried to leave the house that there was no other way to soothe him than to stay home?

Separation anxiety is very common among young children and is typically at its peak between 18 and 24 months of age. When it is severe, a child's distress at his parent's departure can lead to missing critical appointments and can make parents feel angry and guilty. If you can relate to this experience I'm sure you've dreamed for something that could potentially substitute for you-typically Mommy-- and create the feeling of Mommy without you actually being there.

A few years ago I had the idea to develop a garment that could be used to soothe babies and young children who were distraught by their mother's, or primary care-giver's, departure. The garment would be a soft, plush, cotton shirt that the mother would wear for several hours in direct contact with her skin and that then would transform into a blanket to swaddle or otherwise be nestled with her child when she was gone. The garment would be cut and attractively fashioned in such a way that the two permutations were easily and quickly reversible. I called this invention "The Mommy Scented Convertible Cover."

I spoke to my patent lawyer about this idea, and though she thought it was a bit off-beat she didn't dismiss it entirely. To both of our surprise, however, after searching through the existent patent files, she discovered that such an invention already existed! In fact it had been developed by a nurse in Minnesota several years before.

Regina Sullivan and Paul Toubas from the University of Oklahoma studied newborns on a maternity ward separated from their mothers for their responses to the body-odor of "Mommy." At the time of testing the infants were either: (1) calmly awake, (2) crying, or (3) sleeping. They were then presented with either: (a) the hospital gown their own mother had just been wearing, (b) the gown that a mother of another newborn in the maternity ward had been wearing, (c) a clean gown-no one had been wearing, or (d) nothing. Sullivan and Toubas saw that when crying infants were exposed to the gown that their own mother had recently worn they stopped crying. Calmly awake babies also showed extra interest and seemed to be happier when exposed specifically to the gown that smelled like their own mother.

The light-bulb I had for the "The Mommy Scented Convertible Cover" came from knowing about Regina Sullivan's research and the potency of emotional learning with odors. Mommy scent is soothing because the emotions associated to Mama become attached to her scent such that her scent acts as an emotional proxy for Mama herself. A keen observer on a maternity ward would quickly recognize the amazing succor of Mommy's smell. The nurse who figured this out before me must have known firsthand what soothing effects Mommy's scent can have on a distressed infant. The next time you think you'll have a distressing interaction with your toddler before a departure, try gently giving her your recently worn T-shirt or nightgown first and then slip out.

Sullivan, R.M. & Toubas, P. (1998). Clinical usefulness of maternal odor in newborns: soothing and feeding preparatory responses. Biology of the Neonate, 74, 402-408.

Rachel Herz is the author of The Scent of Desire and on the faculty at Brown University.