When acne forms on the butt, it’s because of folliculitis. Folliculitis is usually caused when the Staphylococcus aureus, or staph bacteria, infects a hair follicle. Normally staph bacteria live on your skin without causing problems, but when they get inside through a break in the skin, it results in infection. Why is my bottom spotty? Spots on your buttocks are quite common, and usually caused by a skin condition known as folliculitis which occurs due to irritation, infection or blockage of the hair follicles. It can look like a bumpy rash and occur equally in men and women.