Aside from underlying medical conditions, breakouts in general are often formed as a result of bacteria build up from your pores, or clogged sweat glands. Armpit pimples are no different.
So the first thing you want to ask yourself is “what products am I using in that area that are clogging my sweat glands?” If you haven’t guessed already, YES it can be the aluminum that’s found in your antiperspirant.
Aluminum in antiperspirants and non-natural deodorants is used as a shield against sweat. But in doing so, it forms a barrier to block any sweat from breaking through. This clogs your pores, and can irritate the underarm area, which can lead to unwanted zits.
So if you are using antiperspirants, that is the first thing you want to rule out.