What causes underarm odor?


Raise your hands if you’re sure you know what causes odoriferous armpits.
Raise your hands if you’re sure you know what causes odoriferous armpits.
superpohn/iStock/Thinkstock

How to begin an article on underarm odor. Should we go for the easy opener and imagine a stressful situation in which we curse our foul-smelling sweat? Or conjure the image of a famous sweaty celebrity -- Shaq at the free-throw line comes to mind.

But here's the thing: Your sweat doesn't actually smell. Period. No matter what dripping person or situation you can think of, you're not getting any closer to learning what actually causes underarm odor. So if it's not sweat that's causing you to clamp your arms firmly to your sides on a hot bus ride, what is it?

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Let's first get a little primer on perspiration so that we can get to the root of underarm odor and how sweat contributes to it. Humans have three types of sweat glands: One type is called the eccrine, and that's the kind you'll find on most parts of the body. Palms sweaty before a job interview? Forehead damp during a first date? Those are eccrine glands acting up.

Today we concern ourselves with the apocrine glands. These little pals are the ones that we'll find in places with lots and lots of hair follicles: our groins, for one, and your friendly neighborhood armpits. (There’s also the combo kind first suggested by K. Sato and his colleagues in 1987 that they dubbed apoeccrine glands.) In general, these glands work the same way. The cells in a sweat gland secrete a fluid, and that fluid is largely reabsorbed into the skin when you're at rest or just generally chillin.' However, if it's hot or you're stressed? The volume is a bit greater and can't be fully absorbed. Instead, it's deposited on the surface of the skin. Et voila! Sweat.

In our eccrine glands, the release of that salty fluid is pretty much end of story. But our apocrine glands? They're producing a perspiration that's a bit more interesting than their eccrine pals.

Apocrine glands produce a liquid -- while still odorless -- that contains proteins and fatty acids. It's actually even a milky off-white color, which you probably wouldn't notice, unless you recall that your white T-shirts are mottled with yellow stains in the armpits. Those proteins and fatty acids aren't just causing laundry headaches; they're the key to underarm odor, too.

A Sweat Deal

This is all great for party anecdotes ("Do you know that sweat is odorless? Ooh, Brie!"), but not the least bit satisfying when you're on a crowded subway pushed up against someone's smelly armpit -- or trying to disguise your own.

Because if sweat isn't causing underarm odor, what the heck is? Should you begin to panic that your hygiene is subpar or that you're suffering from an unpleasant genetic abnormality?

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Before you run for the shower or dial your doctor in a fit, relax. While sweat doesn't exactly cause the smell, you wouldn't stink without it. As we said, sweat from eccrine glands isn't much more than water and salt. But our apocrine glands -- which, lo and behold, begin functioning around puberty -- are a more complicated mixture of water, proteins and fatty acids. If the apocrine fluid was deposited on completely sterile skin, we wouldn't smell it either. There's nothing inherently foul-smelling about water, protein and fatty acids.

But the key is that our sweat is deposited on skin spilling over with hungry bacteria. And while those bacteria have no interest in the salty eccrine mixture, our armpit flora are ravenous for the protein-and-fat-filled liquid from our apocrine glands. It's when the bacteria start feeding on it that an odor is released, as the bacteria begins metabolizing. Those looking for bonus points can cite E-3-methyl-2-hexenoic acid (E-3M2H) as a main fatty acid that bacteria eat up [source: Zeng et al.).

So there you have it; there's no smell seeping from your underarms, per se, just hungry bacteria feeding. Of course, not everyone gets "normal" body odor. There is definitely the possibility of "not normal" body odor: this excessive odor is called bromhidrosis. The reason for bromhidrosis could be hyperhidrosis, which is basically excessive sweating. Just remember it's not the excessive sweat that's causing odor, it's that the abundance of moisture leads to an abundance of bacteria that cause the odor.

Naturally, you want to learn a lot more about sweat and underarm odor. Click to the next page to sate your interest and raise your temperature.

Author's Note: What causes underarm odor?

Fun fact: Quite a few people in the world have a gene that doesn't allow them to produce a certain chemical that underarm bacteria love. If you're feeling confident you're one of them, feel free to skip the deodorant -- without that chemical, you're simply not going to have underarm odor. The bacteria don't want you.

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Sources

  • Kanlayavattanakul, M. and Lourith, N. "Body malodours and their topical treatment agents." International Journal of Cosmetic Science. March 15, 2011. (May 7, 2014) http://onlinelibrary.wiley.com/doi/10.1111/j.1468-2494.2011.00649.x/full
  • Mayo Clinic. "Sweating and body odor." Mayo Clinic. (May 7, 2014) http://www.mayoclinic.org/diseases-conditions/sweating-and-body-odor/basics/causes/con-20014438
  • Medline Plus. "Hyperhidrosis." U.S. National Library of Medicine. May 3, 2011. (May 7, 2014) http://www.nlm.nih.gov/medlineplus/ency/article/007259.htm
  • National Health Service. "Body Odour." United Kingdom Government. June 26, 2012. (May 7, 2014) http://www.nhs.uk/conditions/body-odour/Pages/Introduction.aspx
  • Zeng, Chenhui et al. "A human axillary odorant is carried by apolipoprotein D." Proceedings of the National Academy of Sciences of the United States of America. June 1996. (May 14, 2014) http://www.pnas.org/content/93/13/6626.full.pdf+html