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A molecule that plays a role in allowing the body's immune system to recognise its own cells has been shown to be the key to human's ability to recognise their own scent.
The major histocompatibility complex (MHC) has been known to contribute to social communication and mate choice in various animal species, from mice to stickleback fish. A study in 1995 that asked women to pick a mate based on nothing more than their "sweaty t-shirts", indicated that women were more likely to pick a mate who had different MHC genes to themselves -- indicating a relationship between MHC-dependent odor and a person's preference for one odor in a mate over another.
Until now, no previous studies had examined the physiological responses to MHC combinations. The research, carried out by a team of European biologists and published in The Proceedings of the Royal Society B, sought to examine the role that MHC genes plays in humans and our ability to differentiate one individual from another on the basis of smell.
The researchers selected a sample of female participants from Universities of Hamburg and Kiel. Each of the women was provided with perfume-free body soap, untreated cotton t-shirts and two unlabelled bottles, one containing synthesized peptide ligands that would complement their own body's unique blend of MHC, the other containing an MHC masking solvent. The women were directed to shower with the perfume-free soap, and then apply the synthesized peptide solution to one armpit, and the solvent to the other. They were then asked to evaluate the two scents by "sniffing repeatedly from a close distance" and answering whether they would like to wear a perfume that smelt more like their left armpit, or their right.
The results of the test showed that the women preferred their own scent on themselves, as the study explains: "participants considered the modification of their body odour by 'self'-peptides more desirable than the modification by 'non-self'-peptides, indicating that MHC peptide ligands comprise a functionally relevant component of human body odour."
In order to determine that the reactions to the smells were rooted in the brain's responses to the MHC mixes, the research group then carried out a test with functional magnetic resonance imaging (fMRI). Nineteen women took part in the group's trials, where they were placed in an MRI scanner and blasted with twenty second intervals of air directed into their nostrils by a tube. The odorless air would have a different stimuli added to it with each test, containing either the peptide solution that matched their own MHC mix, a peptide solution different to their own MHC mix, a solvent or an additional control odour of peach (peach is known to activate regions of the brain that detect smell).
Eight separate smell sessions were carried out, with the participants asked to indicate how strong each stimuli was. While the peach odour registered strongly, self-peptide and non-self-peptide solutions were shown to be detected supraliminally. Importantly, the self-peptide group activated the right middle frontal region of the brain, a region known to be involved in a human recognising themselves.
The results of the study provide a better understanding of why humans might prefer to wear one perfumed scent (one which might amplify their own MHC scent), but dislike that scent on another individual, preferring a different blend on a potential mate. "If perfumes are indeed chosen to reveal and/or enhance one's own body odour, it is not surprising that one dislikes on others what one likes for oneself," writes the report. "This switch of choice preference with respect to perfume usage might be explained by 'phenotype-matching', a process that is also implicated in kin-recognition."
What is still unknown is exactly how humans detect the mix of MHC evidently apparent in their own scent. While animals such as mice and sticklebacks use a vomeronasal organ, humans don't possess such a mechanism. Further research may identify how humans are able smell these molecules, but if you're looking to go on a successful date in the next few weeks, best find out what perfume your partner likes to wear, and proceed to wear something completely different.
Image: Shutterstock
This article was originally published by WIRED UK
