While dermatologists don't consider pimples on the buttocks to be acne, causes of pimples include an inflammation of hair follicles and boils, Everyday Health explains. An outbreak of pimples on the buttocks is not generally related to any acne issues on other areas of the body.
Pimples on the buttocks are due to the inflammation of hair follicles, which may be due to friction from tight clothing or a bacterial infection, Everyday Health notes. If the inflammation progresses to an infection, painful knots of pus form under the skin, similar to acne cysts. Treatment includes topical or oral antibiotics, depending on the type of breakout the patient is experiencing.