Recent research has shown that we use scent to assess compatibility in finding a partner. Claus Wedekind, a biologist at the University of Lausanne in Switzerland, conducted a study where he gave 44 men T-shirts to wear for two nights in a row. The men refrained from using any scent-based products, so that only their natural scent stayed with the T-shirts (they used scent-free soap and aftershave during this period). Then 49 women sniffed the shirts, and more often than chance, women preferred the shirts of men who were immunologically dissimilar. These women also reported that the scents of their favorite T-shirts reminded them of past and current boyfriends, suggesting that they are consistently choosing partners with the same immunological profile.

So how does immunology affect a person’s scent? Well, there are more than 100 immune system genes known as MHC (major histocompatibility complex). These genes code for proteins that help the immune system recognize pathogens, and they seem to create a certain smell in an individual.

From an evolutionary perspective, partners whose immune systems are different probably produced more disease-resistant offspring. With more immune genes expressed, kids are protected from a wider variety of pathogens and toxins.

It is interesting to note that women in the study were not attracted to T-shirt scents of men with whom they have no immunological genes in common. Too similar and too dissimilar tends to be off-putting, while a middle range is ideal. It is also interesting to note that women outperform men in smell sensitivity tests, which makes sense since they have a greater reproductive investment and must be pickier in choosing a mate. Carol Ober, a geneticist at University of Chicago even found that members of a small religious clan called the Hutterites (which only choose partners within their group of about 40,000), still manage to choose MHC-distinct partners most of the time. In addition, Ober found that couples with high MHC similarity suffered higher miscarriage rates and experienced longer intervals between pregnancies.

The only women who preferred men with similar MHC profiles, were women who were taking the birth control pill. Scientists speculate this is because the pill mimics pregnancy, and the evolutionary advantage may be for women to seek kin as protectors during pregnancy. So could being on the pill cause a woman to choose the “wrong man”? More research needs to be done, but it’s an interesting question!

And if smell is so important, are we ruining our chances of finding the right partner by masking our natural scents with all the scented lotions, deorderants, perfumes, etc. that are available to us nowadays? Well, if you’re really worried, there are actually a lot of quality fragrance-free personal care products available now, so that you can let your true scent shine! But there is evidence that we may purchase scented products that complement and enhance our natural scent rather than mask it. One study found that people with similar MHC profiles tend to choose the same colognes. So could wearing a scented product that you like actually be enhancing your personal scent, and broadcasting it louder? It’s quite possible!

Source: Scents and Sensibility by Elizabeth Svoboda from WebMD feature in Psychology Today Magazine