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

Travis Dixon Biological Psychology, Human Relationships, Key Studies 22 Comments

The sweaty t-shirt study is a classic in evolutionary psychology.

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

Studies have shown that even fish have preferences for MHC genes (Olsen et al. 1998).

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?

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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.

Click the above image to download your free preview of our revision guide.

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)

Comments 22

    1. Post
      Author

      Hi Ferin,

      Regarding pheromones, you could potentially use this study and I know some of the textbooks recommend it. You could argue that it’s the pheromones released in the sweat that are influencing our smell preferences. But personally, I don’t think it’s strong evidence. I prefer experiments that manipulate a putative pheromone (I’ll post some examples soon).

      I think this study is better for evolution, genes and/or formation of personal relationships.

      Here’s a good study for genetic similarity:
      https://www.themantic-education.com/ibpsych/2019/02/11/key-study-the-minnesota-twin-study-of-twins-reared-apart/

      Travis

      Reply

  2. Hi Travis,
    This is an interesting study and this also helps students to know about the pheromones from the other perspective.
    Thank you for sharing it.

    Reply

  3. Hi Travis,

    so this study could be used for hormones influencing behavior, evolutionary explanations of behavior, and (potentially) pheromones?

    Reply
    1. Post
      Author

      I wouldn’t use it for hormones as there is no identifiable hormone in this study, but it could definitely be used for evolutionary explanations of behaviour, and maybe for pheromones, yes.

      Reply
  5. Post
    Author

    Thanks Sophie, I’ve updated the post, including adding the reference and here’s the citation: 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

    and the link: https://pubmed.ncbi.nlm.nih.gov/9787022/

    Reply
    1. Post
      Author
    2. Post
      Author

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  8. Hi there!
    Thank you for all your efforts. If possible, can you please upload one ethical consideration in this study and another study for harmones / pheromones with ethical considerations.
    Thank you

    Reply

  9. hello, question here

    for the syllabus we are supposed to learn one specific pheromone and explain how it influences behaviour. but im lacking the name of the pheromone? is it necessary needed to name a specific pheromone for the exams? or I could just simply use this study.

    Reply
    1. Post
      Author

      As long as you could explain how/why this study MIGHT show the effects of pheromones, that would be OK. I do recommend using a study that manipulates a chemical though, like androstenone or androstadienone.

      Reply

  10. Hi Travis – other textbooks state that this study is a controlled lab experiment. Is this the correct terminology? As the IV has not been manipulated – I don’t want to confuse my students. Quasi conducted under controlled/laboratory conditions perhaps? Thanks for your fantastic resources.

    Reply
    1. Post
      Author

      Hi Kate, I can’t see how this would be a lab experiment since, as you say, the IV hasn’t been manipulated. I think it fits the definition of a quasi/natural experiment.

      Reply

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    1. The participants went about their day out of the lab setting in order to see a cause and effect. I would say it’s a field experiment.

      Reply

  14. Dear Travis,

    I know that pheromones is one of those gray area issues, but Wedekind should not be consider as empirical evidence for pheromones and not only because the original study doesn’t mention them , but because the odours and pheromones aren’t the same. This article offers a clear explanation of why not (it explicitly mentions Wedekind ‘s study):

    The search for human pheromones: the lost decades and the necessity of returning to first principles, written by Wyatt (2015). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4375873/ .

    It explained why MHC is related to odour and matting but it isn’t a pheromone. Looked at the section with the tittle “(c) Not all human smells are pheromones: humans also respond to non-pheromone individual odours”

    As it says at the end of that paragraph, the study investigates the effect of individual odors and possible genetic compatibility, but it does not study the pheromone molecules that will be identical in all males or in all females.The same article states that “Pheromones are signal molecules that are characteristic of, for example, all males of a species, not a particular individual male, though some males may have more of the pheromone and females may prefer these males [5]. Pheromones are not the individual smells that allow animals to be distinguished as individuals”

    Doucet’s study, “The secretion of the areolar (Montgomery) glands of lactating women provokes selective and unconditional responses in newborns”, seems to be better related, since even if it does not identify a specific pheromone the response observed in the babies (sucking and heart rate of babies) were observed in all babies regardless of whether the mother was not their own mother (does not distinguish an individual – who is your mother – but produces the same response in breastfed babies)

    Reply
    1. Post
      Author

      Hi, Yes, I agree it’s not great for pheromones but it’s accepted by the IB. The info you post here would be great for students to revise to add to their essay discussions on the topic. Thanks for sharing!

      Reply

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