Sweaty T-shirt study

In science, the sweaty T-shirt study is a mate selection study, conducted in 1995 by Swiss biologist Claus Wedekind, which found that people are most attracted to the scent of someone of the opposite sex that has the most dissimilar immune system to their own. [1] The results of the sweaty T-shirt study are used by the science-based pair matching site ScienticMatch.com to match people. [2] American anthropologist Helen Fisher calls the sweaty T-shirt study "one of the most important modern scientific studies". [3]

Overview
In the mid 1970s, MHC-dissimilar tendency matching was shown to be the case for mice (and later for other animals such as fish). On this premise, in 1995 Claus Wedekind tested the theory on humans. In this study, Wedekind had a group of female college students smell T-shirts that had been worn by male students for three nights, without deodorant, cologne or scented soaps. Overwhelmingly, the women preferred the odors of men with the most dissimilar MHCs to their own

The theory of desired dissimilar immune system matching can be quantified according to markers on a person’s major histocompatibility complex (MHC), a large gene region that controls the immune system response, and postulates that couples attracted to this type of scent owing to the result that a resultant child would create a more robust immune system, more defensive against a greater variety of pathogens.

History
The idea that MHC genes may confer a distinctive odor, and thereby influence behavior, was first suggested in 1974 by biologist Lewis Thomas. Laboratory studies soon proved Thomas right in the case of mice. Inbred mice, who were alike in all genes but MHC, could detect a difference in the scent of a relative that harbored an ever-so-slightly different MHC gene. Moreover, their odor preferences were not innate but learned. Young mice tend to prefer the odor of their nest mates, but when they hit puberty: they preferred to mate with mice whose MHC genes were unlike their own. [4]

Study
In 1995, Wedekind, a zoologist at Bern University in Switzerland, recruited a group of 49 women and 44 men who harbored a wide range of MHC genes. Wedekind gave each man a clean T-shirt on a Sunday morning and asked him to wear it for two nights. [4] He decided to gather male scent rather than female scent simply because unshaved armpits collect more odor. In fact, to ensure a strong body odor, he gave the men supplies of odor-free soap and aftershave and asked them to remain as "odor neutral" as possible.

On Tuesday morning, the men returned, sweaty T-shirts in hand. Wedekind put each shirt in a plastic-lined cardboard box with a sniffing hole on top. Then he brought in the women. Each was scheduled for the experiment at the midpoint of her menstrual cycle, when women's noses are reputedly the keenest, and each was presented with a different set of seven boxes. Three of the seven boxes contained T-shirts from men harboring MHC similar to the woman's own; three contained T-shirts from MHC-dissimilar men; and one contained an unworn T-shirt as a control.

The women were asked to rate each of the seven T-shirts as pleasant or unpleasant. Overall, says Wedekind, the women he tested were more likely to prefer the scent of men with dissimilar MHC. In fact, that scent tended to remind them of their boyfriends, both past and present. Says Wedekind, "This is the first indication that MHC still plays a role in mate choice today."

References
1. Wedekind, C. et al. (1995). "MHC-dependent preferences in humans." Proceedings of the Royal Society of London 260: 245-49.
2. ScientificMatch.com - homepage .
3. Corcoran, David. (2007). "Helen Fisher Talks About the Sweaty T-Shirt Experiment" (YouTube). New York Times (Science), On Desire: with David Corcoran and Helen Fisher, 10 April.
4. Richardson, Sarah. (1996). “Scent of a Man”, Discover Magazine, Feb.

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