A boil is a skin infection that starts in a hair follicle or oil gland. … After four to seven days, the lump starts turning white as pus collects under the skin. The most common places for boils to appear are on the face, neck, armpits, shoulders, and buttocks. When one forms on the eyelid, it is called a sty.
Boils are usually caused by a bacteria called Staphylococcus (staph). Some staph infections develop into abscesses and can become serious very quickly. This germ can be present on normal skin and enters the body through tiny breaks in the skin or by traveling down a hair to the follicle.
This is an interesting question and the simple answer is: yes — antiperspirants can cause armpit cysts. According to Medline Plus, cysts on the surface of the skin in the armpit may be caused by shaving or antiperspirants. Apparently deodorants do not cause cysts in the armpit.