Boils or infection in the armpit can be of two major varieties. One is chronic, which keeps coming and going over a lot of years. That is actually a medical condition. The other is acute. It just happened, and it happens only once a while, not every time. In the acute phase, it is generally because of trauma, say after waxing or a hair pull or maybe similar problems which can be treated by antibiotics. The second one is chronic, is generally because of a medical condition called hidradenitis sup