Key Study: “The Sweaty T-shirt Study” (Wedekind et al. 1995)

Updated June, 2020

Can we smell someone’s genes? Not their trousers, but their genetics. The Swiss Biological Researcher Claus Wedekind and his colleagues conducted a famous study to see if our preference for smells is linked with our genetics. In other words, they wanted to see if we prefer the smell of someone who has genes that would be a good match with ours. 

Background Information

MHC Genes are a large group of genes responsible for the development of the immune system. Different genes protect against different infections, so the healthiest individuals would have the largest range of MHC genes because this would mean their immune systems would be able to fight a wider range of diseases. This makes them healthier and more likely to survive and pass on genes (which is the purpose of life on this planet). It therefore makes sense then that we would want to procreate with someone who has very dissimilar (i.e. different) MHC Genes to us, so our offspring are well-protected against an array of diseases.

Yamazaki et al. (1976) showed this to be the case for male mice, who show such a preference for females with different MHC genes. Studies on fish have also shown that they show preferences for waters depending on MHC scents (Olsen et al. 1998). So while these animal studies show MHC genes can influence behaviour, can we say the same for humans?

Read More:

• Key Study: Evolution of Gender Differences in Sexual Behaviour (Clark and Hatfield, 1989)
• What is a pheromone?
• Key Study: Buss’ cross-cultural study on mate preference (1989)

The Sweaty T-Shirt Study Methods

Wedekind’s study is often known as the “sweaty t-shirt study”. The researcher (Wedekind) assembled volunteers, 49 women and 44 men selected for their variety of MHC gene types.

The women were asked to record whether or not they were taking oral contraceptives (e.g. the pill) as this would affect the results because it affects levels of hormones.

The men were given a clean cotton t-shirt and were asked to keep it in an open plastic bag when not wearing it. They wore the same t-shirt for 2 nights when they were sleeping. They were also asked to abstain from spicy foods and other activities that may affect the smell of the T-shirts (e.g. smoking or sleeping with someone else in their bed). They were also given odour free deodorants. They kept the shirts in open plastic bags when they weren’t wearing them.

Starting the day after the men wore the shirts, they were then put into identical boxes equipped with a smelling hole and invited the women volunteers to come in, one at a time, and sniff the boxes. Their task was to sample the odor of six boxes and to rate each t-shirt on a scale of 1-10 in terms of its intensity, pleasantness, and sexiness. There were three t-shirts that were similar MHC Genes, and three that were from men with dissimilar MHC Genes. Where possible, the timings of the smells were times for the second week of the women’s menstrual cycle.

A Note On Pheromones: If you are using this study for your IB Psychology exams, be careful with using it for a demonstration of how pheromones can influence behaviour. While the effect on smell preference could be a result of pheromones, personally I prefer using studies focusing on putative human pheromones, like androstadienone or androstenone. In Wedekind et al.’s original paper, pheromones aren’t mentioned at all. 

Results and Conclusions

Overall, the women who were not on the pill preferred the scents of T-shirts worn by men whose MHC genes were different from their own. Another interesting finding was that the “….odours of MHC-dissimilar men remind the test women more often of their own actual or former mates than do the odours of MHC-similar men.” This suggests that it’s not just in the lab that the women preferred these smells but they might be reflective of what happens in the real world, too.

The researchers concluded that MHC genes and their associated smells influence mate preference.

Critical Thinking Considerations:

• How and why have we evolved to find some people’s smells more attractive than others?
• How does this study show the influence of genes on behaviour?
• Could this study be used as evidence for the existence of human pheromones? Why?
• What are the limitations of this

References
Claus Wedekind; Thomas Seebeck; Florence Bettens; Alexander J. Paepke. MHC-Dependent Mate Preferences in: Biological Sciences, Vol. 260, No. 1359. (Jun. 22, 1995), pp. 245-249. (Link)

OlsÉn KH, Grahn M, Lohm J, Langefors Å. MHC and kin discrimination in juvenile Arctic charr, Salvelinus alpinus (L.). Anim Behav. 1998;56(2):319-327. doi:10.1006/anbe.1998.0837 (Link)