How Does It Work? Deodorant and Antiperspirant

When I’m about to start my period. On job interviews. When I have the flu. When it’s really hot outside. When I have to run for more than eight seconds. When I have to give speech. Even for someone like me, who doesn’t sweat a lot, there are times when my armpits devolve into a swampy mess. Deodorant and antiperspirant are two different methods of averting that “teenage boy’s locker bag” smell.

I usually think of deodorant and antiperspirant as being essentially the same thing. When I refer to by antiperspirant, I call it deodorant. However, deodorant and antiperspirant work by completely different mechanisms. They are also regulated differently. Deodorant is regulated by the FDA as a cosmetic, whereas antiperspirant is an over-the-counter drug.

To understand how deodorant works, you first need to understand one important thing: it’s not your sweat that stinks. Your sweat comes out of your body smelling just fucking fine. The problem is that your armpits are bacteria heaven. First of all, they are moist. Secondly, they are intertriginous, meaning that two pieces of your skin are touching each other. Finally, the pH of your armpits is slightly higher than the rest of your skin. The rest of your skin is slightly acidic, which kills off a lot of bacteria; your armpits are much more neutral, making them prime for bacteria breeding. The apocrine and eccrine sweat glands pump out moisture into your underarm region. This feeds the generally benign bacteria living in your pits. In particular, Corynebacterium striatum is known to convert odorless precursors into trans-3-methyl-2-hexenoic acid. This molecule smells like, well… armpits. The way that we don’t want our armpits to smell. These bacteria also break down lipids in your sweat into smaller components such as butyric acid, which is sometimes used in stink bombs.
Of course, it’s not a single bacteria responsible for your stinkiness. If any of you have armpits that smell like vinegar, it’s likely the fault of certain Propionibacterium, who can break down amino acids into the pungent propanoic acid. If you smell more like a very aromatic Époisses de Bourgogne, it’s probably due to Staphylococcus epidermidis, which can convert the essential acid leucine into 3-methylbutanoic acid, which smells like dirty feet or smelly cheese. Both genetic and environmental factors contribute to which bacteria are most comfortable hanging out on your skin.Since there are multiple chemical processes that contribute to body odor, interfering with them all would be a nightmare. So, instead, they are developed to prevent the bacteria that make you smell from wanting to spend a lot of time in your armpits. Deodorant and antiperspirant employ two different mechanisms to solve that problem.Deodorants create a hostile environment for bacteria in a variety of ways. First of all, they lower the pH of your armpit. As a result, the skin under your arms is more similar to the rest of your skin. It’s slightly acidic and, thus, a crappy place for bacteria to grow. They’ll also typically have some sort of alcohol, which can help kill those pesky bacteria. Some will also have other antimicrobial agents. Virtually all will have some sort of scent to help mask any ickiness that managed to develop anyways. You’ll still have sweaty pits, but you shouldn’t stink.

Antiperspirants, on the other hand, work by preventing you from sweating. Consequentially, the bacteria have nothing to convert into nasty-smelling molecules. Antiperspirants contain aluminum-based compounds such as aluminium chloride or aluminium chlorohydrate. The aluminum ions are taken into the cells around the ducts. As a result, water also begins to pass into those cells. These cells begin to swell, closing the ducts and preventing sweat from escaping until the swelling goes back down. Antiperspirants will also typically contain the same sorts of ingredients as deodorant, meaning that they perform double duty. Prescription-strength antiperspirants use the same active ingredients and mechanisms, but at higher concentrations.

Either way, the goal is to leave you smelling like roses. Or, you know… pomegranate and lemon verbena. Whatever.


1. Hey I know you like Lorac eye primer and just wanted to let you know it’ll be $10.50 on Sept 17th at Ulta(I’m sure you already know but in case not..). Is it totally creepy that I remember an internet stranger’s eye primer preferences?

2. Ha, you’re so sweet! Thank you!

3. Do the aluminium-based compounds cause dark armpits?

4. I can’t find any evidence that is not anecdotal that suggests that that is the case.

5.  Great post – thank you.

Would you do a beauty bullshit post on nail polish/ nail strengtheners/ nail whatevers. As a thin-nail challenged person I’ve found the claims to be spurious, but the companies love to use scientific sounding language about polymers and such and say things like : Exposure to natural light secures the patent-pending Pro-Light technology, creating an enduring, long-lasting polish…

Pro-light technology! Sounds fancy!

6. That’s a good idea! Thanks!

7. Hilarious and informative, love it!

Adding to your ever-growing request for posts: I’d love to hear your thoughts on tube-forming mascaras. I love my Trish McEvoy “lash curling” tubular mascara for it’s smudge-proofiness, ease of removal, and contact-lens/sensitive eye friendliness. But it definitely doesn’t offer the same POW! volume as other types.

8. Do you just want a review?

9. Totally, if you’ve got any in your aresenal! I’ve never tried any of the other brands, Blinc’s intrigues me (but I think it’s two step?)

Or even a breakdown of how tube mascaras work – to me it seems the formula adheres to itself as it dries rather than the lash – which is great for removal but not so great for building up product/layering on.

10. I really love your blog – especially the methodical approach to mega comparisons. You mentioned that you used to have a lot of black eyeliner pencils. Could you consider doing a mega comparison on black eyeliner pencils, looking at the staying power and how black each are?

11. Wow, did you find all that information online or are you a chemistry student or something? I cannot imagine another beauty blogger to know all this stuff!

12. Out of curiosity, what happens to the sweat when it can’t escape through your pits? Does it just absorb back into your body? Do we know?

13. Do all anti-perspirants contain aluminum? I am really allergic to most metals, and I find that I get a bad rash with almost every deodorant I used. I tried the Toms all natural deodorant, but that of course didn’t do anything for my sweatiness.