The findings of a recent University of Essex study, which disclose a likely genetic basis for individual variations in sensitivity, are important in many ways. First, we can discern a mechanism behind some people's pronounced sensitivity. Second, we can see how off-base the "nature versus nurture" debate is (or was). But third, there are significant implications for personal health. Quoting Dr. Elaine Fox, the lead researcher: "This opens the door to the idea of personalized treatments for anxiety disorders. Information about the genotype...of a patient could be used to inform decisions about which treatments...are likely to be most effective." (link:

The prospects are actually more intriguing - and more potentially useful - than that. All we need do is consider a particular framework for sizing up this most salient distinction between people, i.e., how much ‘gets' to them and how they handle it. This framework, known as Boundaries, opens the door to a whole different way of viewing health care and assessing both individuals' vulnerabilities and the treatments most likely to help them.

The Boundaries Concept

Because we are bounded within our bodies, we are enabled to have distinct minds and personalities. The Boundaries concept, developed by Ernest Hartmann, MD, of Tufts University, is an especially useful way of looking at personality differences - and understanding why one person may develop a chronic illness that is distinctly different than another.

Boundaries are more than a measure of introversion or extroversion, openness or closed-mindedness, agreeableness or hostility, or any other personality trait. Boundaries are a way to assess the characteristic way a person views her/himself and the way s/he operates in the world based on how that person handles the energy of feelings. To what extent are stimuli let in or kept out? How are a person's feelings processed internally? Boundaries are a fresh and unique way of evaluating how we function.

According to Hartmann, each of us can be characterized on a spectrum of boundaries from thick to thin. In his words:

There are people who strike us as very solid and well organized; they keep everything in its place. They are well defended. They seem rigid, even armored; we sometimes speak of them as "thick-skinned." Such people, in my view, have very thick boundaries. At the other extreme are people who are especially sensitive, open, or vulnerable. In their minds, things are relatively fluid...Such people have particularly thin boundaries....I propose thick and thin boundaries as a broad way of looking at individual differences. (Hartmann 1991)

Hartmann first came to his conception in an interesting way. In the 1980s, he was studying people who have nightmares and noticed that they could also readily recall other vivid or colorful dreams even if they didn't qualify as nightmares. These people seemed to him especially "sensitive," "vulnerable," or "imaginative," in contrast with other people who came across as more "solid," "stoic," or "persevering." He suspected that there are real brain and body differences between thin and thick boundary people, and he developed a questionnaire to gain more insight.

Since the 1980s, at least 5,000 people have taken Hartmann's Boundary Questionnaire (BQ) and more than 100 published papers have referenced it. The scores on the BQ are distributed across the spectrum of boundaries in a Bell-shaped curve. Women tend to score significantly thinner than men, and older people tend to score somewhat thicker than younger people. (Hartmann, et al 2001)

Thick and Thin Boundaries

The accumulated evidence shows that thin boundary people are highly sensitive in a variety of ways and from an early age:

- They react more strongly than do other individuals to sensory stimuli and can become agitated due to bright lights, loud sounds, particular aromas, tastes or textures.
- They respond more strongly to physical and emotional pain in themselves as well as in others.
- They can become stressed or fatigued due to an overload of sensory or emotional input.
- They're more allergic and their immune systems are seemingly more reactive.
- And they were more deeply affected - or recall being more deeply affected - by events during childhood.

In a nutshell, highly thin boundary people are like walking antennae, whose entire bodies and brains seem primed to notice what's going on in their environment and understand more precisely what it means. (Aron 1996)

Thick boundary people, on the other hand, are fairly described as stolid, rigid, implacable, or thick skinned:

- They tend to brush aside emotional upset in favor of simply handling the situation and maintaining a calm demeanor.
- In practice, they suppress or deny strong feelings. They may experience an ongoing sense of ennui, of emptiness and detachment.
- Experiments show, however, that thick boundary people don't actually feel their feelings any less. Bodily indicators (e.g., heart rate, blood pressure, blood flow, hand temperature, muscle tension) betray their considerable agitation despite surface claims of being unruffled. (Lynch 1985)

In sum, highly thick boundary people don't take in nearly as much in their environment and they are much slower to recognize what they're feeling. However, they are affected just as much as thin boundary people by what's happening within.


Aron, Elaine. The Highly Sensitive Person: How to Thrive When the World Overwhelms You. New York: Carol Publishing Group, 1996, 7.

Hartmann, Ernest. Boundaries in the Mind: A New Dimension of Personality. New York: Basic Books, 1991, 4-7.

Hartmann, E., Harrison, R., and Zboroski, M. "Boundaries in the Mind: Past Research and Future Directions." North American Journal of Psychology 3 (June 2001): 347-68.

Lynch, James J. The Language of the Heart: The Body's Response to Human Dialogue. New York: Basic Books, 1985, 209-13, 220-22.

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