Acne occurs mainly on the face and is caused by the local storage of sebaceous material in the skin when it is blocked from excreting. Acne rarely occurs on the arms, but peri-hair keratosis can occur on the arms, mainly on the upper arms where the skin is rough, the hair follicles protrude like goose bumps, and hair penetration out of the skin is obstructed, which is a genetic skin disease. Treatment can be done by applying topical retinoic acid preparations, such as 0.1% retinoic acid cream, which have the function of exfoliating, dissolving acne and promoting normal epithelial metabolism. You can also apply topical moisturizing and emollient skin care products, which are helpful in improving skin inflammation and roughness. Some patients can also go to the hospital for chemical peeling treatment, which is also beneficial for improving symptoms.