The condition of small bumps on the arms may be related to folliculitis, keratosis pilaris, solar dermatitis and other factors. 1. Folliculitis: this is an inflammatory skin disease mainly involving hair follicles, can occur in any part of the body, mainly associated with bacterial and other pathogens infected hair follicles, especially in the case of often wearing insulated, closed items, such as wearing long rubber gloves for a long time, which can lead to the symptoms of the patient’s arm with small bumps. 2. Keratosis pilaris: this is a chronic follicular keratosis pilaris skin disease, there is a clear genetic predisposition, but also may be related to vitamin deficiency, metabolic disorders, etc., occurring on the outside of the upper arm as well as the anterior side of the thighs, generally without treatment. 3. solar dermatitis: this is due to the skin exposed to ultraviolet light and the local inflammatory reaction, the patient’s arm will have small red bumps, accompanied by redness, burning, itching and pain and other symptoms. Small bumps on the arm may also exist other causes, so should seek medical attention to clarify the diagnosis, so as not to delay the condition.