Does 3 day deodorant really work?

QM’s query…The boyfriend and I were watching tv and there was an ad about a drugstore-brand deodorant that touted “3-day efficiency”.
Me : “3-day efficiency ? Does it means that you’re supposed to go 3 days without washing your armpits ? Ewwww !”
Him : “Well, deodorant crawls into the sweat thingies on your skin and block odors from inside. So it can be efficient for 3 days even if you wash the skin in between”.

(OK, none of us are cosmetic scientists, as you can guess from all these technical terms) Which one of us is right ? I thought that OTC skin products can’t legally seep into the skin, but maybe it’s different for deodorants and the like.

The Beauty Brains respond

First a question: are you and your main squeeze talking about deodorants or antiperspirants (APDs)? Here’s why it matters:

APD vs Deo for B.O.

Deodorants just stop odor (by covering up with fragrance and by killing odor-producing bacteria.) APDs prevent you from sweating (or by at least reduct the amount of sweat) and less sweat = less odor because the actual stink is caused by bacteria munching on fatty acids that are contained in your sweat. Since your boyfriend referenced that the product “crawls into the sweat thingies,” I’m assuming that your asking about the “plugging” kind of products so here’s the deal:

Antiperspirants plug your pits

The aluminum salts in APDs migrate inside your sweat ducts where they react with moisture to form Gelatinous Little Plugs. (That sounds like the name of a band but it’s not. As far as I know.) These plugs prevent sweat from soaking your armpits and therefore keep you relatively stink-free. If you stop using an antiperspirant it takes a few days for the sweat glands to clear themselves of all these petite plugs, which is why the sweat-reduction effect can last last for a few days – even is you shower!

This phenomenon is not unknown to advertisers: I remember seeing ads for Mitchum brand antiperspirant that claimed it was “so effective you can skip a day.” I’m pretty sure that claim was based on the sweat gland retention of gelatinous aluminum salt plugs. Anyway, what does all this mean? Your boyfriend is right! What did he win?

PS: APDs ARE over the counter drugs because they have a physiological effect on skin. Cosmetics can’t affect body function (according to US law, at least.)