Hair on the buttocks is anal hair in most cases, which is a normal phenomenon; pigmented moles or local drug adverse reaction will also have buttocks hair, although it is a pathological condition, but usually has no effect on health. 1. Anal hair: most of the hair on the buttocks grows around the anus, also known as anal hair. Anal hair is more common in men than in women, and has a certain physiological role in preventing microorganisms such as bacteria or debris from entering the anus, and helps keep the perianal area dry and breathable. 2. Pigmented nevus: It is a benign skin tumor, many people have it after birth, and it can appear anywhere in the body. They appear as black bumps on the skin with a small amount of hair in the middle of the bumps, and the hair on the nevus is usually thicker and longer than the hair on other parts of the body. Pigmented nevus is usually benign, if there is local pain, redness around the nevus or the nevus becomes bigger and darker, it needs to be removed in time. 3. Adverse reaction of local medication: long-term use of glucocorticoid-containing medication on the buttocks will lead to exuberant growth of local skin hairs, and the hairs will obviously become more and more long. It can recover by itself after stopping the drug, but the recovery time is longer. If the above situation occurs, it is recommended to go to the hospital and have a doctor make a clear diagnosis after a comprehensive evaluation and treat the symptoms.