P.U.! Who stinks? There’s nothing like a sweaty, stinky armpit to ruin a job interview or first date. But there’s more to body odor than just passing the sniff test. The way we smell can reveal a lot of information about our health, personality traits, and even dating preferences Paternally inhereited HLA alleles are associated with women’s choice of male odor. Jacob, S., McClintock, M.K., Zelano, B., et al. Institute for Mind and Biology and Department of Psychology, The University of Chicago, Illinois. Nature Genetics 2002;30(2):175-9. Individuals reporting idiopathic malodor production: demographics and incidence of trimetylaminuria. Wise, P.M., Eades, J., Tjoa, S., et al. Monell Chemical Senses Center, Philadelphia, PA. The American Journal of Medicine 2011;124(11):1058-63. .

Make ’Em Sweat — The Biology of Body Odor

Everyone’s got body odor — even those who think their (pits) don’t stink. But not all odors are repulsive or the kind easy to get rid of with a stick of Degree. The biology behind body odor is pretty tricky, but it’s partially based on three types of glands that contribute to odors. Sweat glands exist all over the body and kick into gear when we exercise, become overheated, or feel anxious. Sebaceous glands are also found throughout the body and only start producing their oily liquid during puberty. Apocrine glands, located mostly in the armpit and pubic regions, also start acting up around adolescence and can cause some serious stink. Steroids in apocrine secretions, especially the ones that come from the armpit, are some of the biggest culprits behind adult B.O. But — here’s a real shocker — sweat and other secretions don’t actually smell. Sweat, sebaceous, and apocrine glands secrete volatile organic compounds, and odors arise when these “VOCs” interact with bacteria on the skin, in hair follicles, and in the mouth.

While it might be possible to avoid bad B.O. by steering clear of certain foods, how we smell is largely based on genetic factors. Studies have found identical twins smell pretty much the same, even when they don’t live together Body odour of monozygotic human twins: a common pattern of odorant carboxylic acids released by a bacterial aminoacylase from axilla secretions contributing to an inherited body odour type. Kuhn, F., Natsch, A. Analytical Chemistry, Duebendorf, Switzerland. Journal of the Royal Society 2009;6:377-92. . Ethnic background also comes into play: People of East Asian descent tend to sweat less and have less body odor than those of African and European descent A strong association of axillary osmidrosis with the wet earwax type determined by genotyping of the ABCC11 gene. Nakano, M., Nobutomo, M., Akiyoshi, H., et al. Department of Reconstruction and Plastic Surgery, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki, Japan. BMC Genetics 2009;10:42. . And elementary school girls are right that boys stink, since men tend to have stronger body odor than women.

Genetics can influence our ability to detect certain odors, too. As anyone who’s walked into a boys’ locker room can guess, women are generally more sensitive to body odor than men are. Some researchers suggest this is because throughout history, women have had to be pickier about choosing the right mate. And people react completely differently to certain odors because of their unique DNA. Take androstenone, one of the steroids in human sweat and urine. Some people say it smells like vanilla, others find it appeals to their nostrils as much as sweat or urine, and some can’t smell it at all.

B.O. You Can Be — What Body Odor Communicates

But body odor can reveal more than just whether someone used deodorant today. Want to know if a new pal’s outgoing, neurotic, or bold? Try taking a whiff of his/her armpit. (Proceed with caution.) There’s some evidence people can predict certain personality traits just by sniffing odor samples. Body odor also has a lot to do with romantic attraction — beyond the fact that it’s a good idea to deodorize before a date. Sweat, skin oils, and other secretions release pheromones, molecules that help animals communicate. In humans, pheromones can convey important information about who’s a potential match — no OkCupid profile required.

Studies have found women are most attracted to the odors of (and most likely to smooch!) men whose genes are different from theirs Paternally inhereited HLA alleles are associated with women’s choice of male odor. Jacob, S., McClintock, M.K., Zelano, B., et al. Institute for Mind and Biology and Department of Psychology, The University of Chicago, Illinois. Nature Genetics 2002;30(2):175-9. . In other words, women seek out partners who’ll give them the best chance of producing healthy kids. So swap the Chanel No. 5 for some eau de fertility: Smells have a lot to do with women’s reproductive cycles. Women find high-testosterone odors more attractive when they’re most fertile, while men find fertile women smell sexiest Body odor attractiveness as a cue of impending ovulation in women: Evidence from a study using hormone-confirmed ovulation. Gildersleee, K.A., Haselton, M.G., Larson, C.M, et al. Department of Psychology, University of California, Los Angeles, CA. Hormones and behavior 2012;61(2):157-66. . And certain oral contraceptives don’t just change women’s menstrual cycles — they can also make ladies less likely to sniff out a potential mate. One study found women on a birth control pill were less likely to prefer the odors of men with compatible genetic profiles.

Back in the caveman days, our nostrils may have also helped us avoid incest. It’s still not clear whether family members can recognize each other’s smells, and people might only develop the ability once they hit adulthood Family scents: developmental changes in the perception of kin body odor? Ferdenzi, C., Schaal, B., Roberts, S.C. Evolutionary Psychology and Behavioral Ecology Research Group, University of Liverpool, Liverpool, UK. Journal of Chemical Ecology 2010;36(8):847-54. . Some research suggests humans are especially skilled at sniffing out same-sex siblings Possible olfaction-based mechanisms in human kin recognition and inbreeding avoidance. Weisfeld, G.E., Czilli, T., Phillips, K.A. Department of Psychology, Wayne State University, Detroit, MI. Journal of Experimental Child Psychology 2003;85(3):279-95. . But there are certain situations when body odor indicates a serious health issue.

Battling B.O. — Body Odor Disorders

In most healthy adults, body odor isn’t a problem that deodorant and a regular shower routine can’t take care of (although some people might smell just fine going au natural). But there are certain foods, habits, and medical conditions that can have friends and coworkers wearing face masks. Foods like garlic and curry can cause some smelly situations, since they contain chemicals that our glands excrete onto the skin. And burger-lovers beware: Some women think men who eat a lot of red meat smell worse than those who take their meals with a little less beef The effect of meat consumption on body odor attractiveness. Havlicek, L, Lenochova, P. Department of Anthropology, Faculty of Humanities, Charles University, Prague, Czech Republic. Chemical Senses 2006;31(8):747-52. .

But if something smells fishy, it might be a case of trimethylaminuria, a condition in which the body can’t break down certain chemicals, instead emitting the odor of (gulp) rotting fish Individuals reporting idiopathic malodor production: demographics and incidence of trimetylaminuria. Wise, P.M., Eades, J., Tjoa, S., et al. Monell Chemical Senses Center, Philadelphia, PA. The American Journal of Medicine 2011;124(11):1058-63. . A sudden change in body odor might also indicate a health issue like diabetic ketoacidosis or kidney failure. There’s some research suggesting schizophrenic patients also have a distinct body odor — though it’s unclear exactly what causes the smell Identification of schizophrenic patients by examination of body odor using gas chromatography-mass spectrometry and a cross-selective gas sensor array. Di Natale, C., Paolesse, R., D’Arcangelo, G., et al. Department of Electronic Engineering, University of Rom Tor Vergata, Rome, Italy. Medical Science Monitor 2005;11(8):CR366-75. Olfactory sensitivity through the course of psychosis: Relationship to olfactory identification, symptomatology, and the schizophrenia odor. Brewer, W.J., Wood, S.J., Pantelis, C., et al. ORYGEN Research Centre, Melbourne, Victoria, Australia. Psychiatry Research 2007;149(1-3):97-104. . If bad body odor is an issue, it’s a good idea to speak to a health professional to rule out any serious causes.

There are a few easy ways to combat B.O: Bathe regularly, wear fresh clothes, and apply deodorant daily. (Some people say antiperspirants pose health risks, but the research is unclear.) And don’t forget to wash and dry feet and wear clean socks. B.O., be gone!