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It's What Online Dating Can't Tell You

Body odour is important.

Jason Salmon/Shutterstock
Source: Jason Salmon/Shutterstock

Despite the numerous success stories associated with the use of online dating apps and sites, how much can they really tell about compatibility? Information about as a person’s interests, hobbies, likes and dislikes, can be conveyed online, but there are obviously many characteristics of a person that we can only ascertain by meeting face-to-face. One of these is a person’s body odour, and we are not referring here to the quality of their perfume or cologne, but rather a person’s natural odour, which research has long since told us to have a significant influence on our perception of whether or not we might ultimately find someone sexually attractive and compatible.

Attractiveness and Body Shape

One illustration of how this works has been demonstrated in studies of body shape. Most of us have bodies which are more or less symmetrical, for example, our left foot is about the same size as our right; our left ear is a similar size to our right. However, each of us deviate slightly from perfect symmetry and one factor which causes us to have these small deviations from symmetry are genetic mutations. A mutation is a form of damage to the DNA in our genes which may have the effect of preventing a gene from functioning properly. Therefore, as symmetry is an outward or phenotypic indicator of good genes, free from mutations, it follows that the more symmetrical a person is, the healthier they are likely to be and as health is attractive, then symmetry is itself attractive.

But how is this related to body odour? This was illustrated experimentally in the study of Thornhill & Gangstead (1999), who measured male and female research participants for symmetry and then got them to wear a t-shirt in bed for two nights, with explicit instructions to wash their bed sheets with unscented detergent and themselves refrain from using deodorants, drinking alcohol, using tobacco and to sleep alone. After wearing the t-shirts for the specified period, the participants were instructed to place them in a plastic bag. Opposite sex judges then rated the odour of each t-shirt for pleasantness, sexiness and intensity. They found that females who were ovulating normally (not taking a contraceptive pill) preferred the scent of men who were more symmetrical in shape to those who were less asymmetrical, although this was only the case during the period of peak fertility. However, the researchers did not find that males preferred the scent of symmetrical females to be more attractive than asymmetrical females. The study demonstrates that to females, pleasant male odour is a signal for health and attractiveness.

Sexual Compatibility

One other specific type of information available to us from a person’s body odour is their genotype, or type of genes they have at what is called the Major Histocompatibility Complex (MHC). The MHC is a group of genes which plays an important role in our immune functioning or in other words our capability to protect ourselves from disease. These genes vary greatly across the population, with everybody having different versions or types of these MHC genes.

A person’s body odour is related to the type of MHC genes they possess, so therefore we can use our olfactory senses to identify potential sexual partners according to their MHC genes. More specifically we need to determine whether potential partners are either MHC similar or MHC dissimilar to ourselves.

Evidence for this comes from a study carried out by Santos, Schinemann, Gabardo & Bicalho (2005) who investigated the relationship between human MHC dissimilarity and the subjective pleasantness of specific body odours collected from members of the opposite sex. Firstly, body odours were obtained from the urine and sweat of 58 student participants. Next, the researchers got female and male participants to smell and rate the odour samples which had been collected from participants of the opposite sex. They found that when females smelled male odours, pleasantness ratings were related to MHC dissimilarity. In other words females preferred the odour of males who had MHC genes dissimilar to themselves. However, the researchers found no relationship between MHC dissimilarity and pleasantness ratings when the males smelled the female odours.

The suggestion is that male body odour is a significant factor in mate choice for females, but female odour is not necessarily important as a cue for mate choice in males. Perhaps this is because visual cues are more powerful in what triggers a man’s sexual attraction.

What is the Adaptive Advantage of Identifying MHC Dissimilarity?

Having children with those who have dissimilar MHC genes or ‘MHC disassortative mating’ can convey at least two advantages.

  • It is possible that those who have similar genes are more likely to be more closely related to us. Reproducing with close genetic relatives could mean that the offspring will be weaker, have lower intelligence and possess other possible genetic defects. However, someone who has dissimilar MHC genes might also have other dissimilar genes, meaning that the above scenario is avoided.
  • Secondly, reproducing with a person with dissimilar or complementary MHC genes will have the advantage of increasing the chances of genetic variation in the offspring meaning that they will possess better immune functioning, or enhanced immunocompetence, the consequence of this is that offspring will be stronger in being better able to fight off disease.

Body Odour and Attraction

One final study suggesting that body odour is a significant factor in attraction comes from the work of Garver-Apgar, Gangestad, Thornhill, Miller & Olp (2006), who investigated MHC similarity in 48 romantically involved couples. Participants completed a series of questionnaires, including relationship satisfaction; partner investment; number of sex partners, and willingness to have sex without emotional closeness, as well as being assessed for MHC type. The researchers found that as MHC similarity increased, then female sexual responsiveness to their partner decreased. In addition they found that as MHC similarity increased, female satisfaction with the extent to which their partner aroused them decreased. Finally the researchers found that females who were MHC similar to their partner reported more attraction to other men and also reported an increased number of affairs.

Females frequently report that the scent of a male is one of the most important cues they use in partner choice, as well as playing a part in sexual arousal (Hers & Cahill, 1997). Body odour is used for detecting a male’s health and genetic compatibility, with female sense of smell is at its height around the period of ovulation, the time of the month when pregnancy can occur (Doty, 1981). Males however rate female body odour and visual appearance as equal in importance for attraction. Overall then body odour is a vital cue for what we find attractive, and is a factor that obviously cannot be ascertained simply through an online liaison. Until there is a way of discovering how someone smells through online interaction, we really need to meet face-to-face before engaging in any kind of relationship commitment.

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  • Doty, R.L. (1981) ‘Olfactory communication in humans’. Chemical Senses 6, 351–376.
  • Garver-Apgar, C. E., Gangestad, S. W., Thornhill, R., Miller, R. D. & Olp, J. J. (2006) ‘Major Histocompatibility Complex Alleles, Sexual Responsivity, and Unfaithfulness in Romantic Couples’, Psychological Science, 17, 830-835.
  • Herz, R. S. & Cahill, E. D. (1997) ‘Differential us of sensory information in Sexual Behaviour as a function of gender’, Human Nature, 8, 275-286.
  • Santos P.S.C, Schinemann J.A, Gabardo J, & Bicalho M.D. (2005) ‘New evidence that the MHC influences odor perception in humans: a study with 58 Southern Brazilian students. Hormones and Behaviour. 47, 384–388.
  • Thronhill, R. & Gangstead, S. W. (1999) ‘The scent of Symmetry: A Human Sex Pherome that Signals Fitness’ Evolution and Human Behaviour, 20, 175-201.