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?
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.
- 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