Pimples on the backside develop due to the same factors that cause them elsewhere in the body, primarily build-up of dirt and/or oils, skin irritation and other forms of breakouts. According to the Huffington Post, people more likely to break out on the face are also more likely to break out elsewhere on their bodies.
The same rules regarding treatment and prevention of acne on areas such as the face and chest also apply to the backside. Medical aesthetician Giselle Curcio outlines several ways to prevent "butt acne," including wearing breathable material such as cotton. Nylon underwear tends to trap perspiration, which can lead to irritation and acne. Keeping the body clean provides one of the first lines of defense in preventing acne so as not to allow dirt, oils and sweat to accumulate on the skin for long periods of time. Exfoliating also decongests pores, which diminishes the appearance of acne and helps prevent further breakouts in the area. Using acne-fighting ingredients such as salicyclic acid also helps to get rid of butt acne, providing a chemical exfoliation. In addition, Benzoyl Peroxide-based products are effective against all sorts of acne because they cause the bacteria associated with various sorts of pimples.