Small black spots on the body may be caused by solar dermatitis, post-inflammatory hyperpigmentation, hormone level disorders and other factors. 1. Solar dermatitis: if exposed to the sun for a long time, the ultraviolet rays of the sun will damage the local skin barrier, thus releasing inflammatory cytokines, which will enhance the aminotransferase enzyme of melanin synthesis, promote melanin synthesis, and make the patient have the symptom of small black spots on the body. 2. Post-inflammatory hyperpigmentation: if the patient has suffered from urticaria, eczema and other diseases, the inflammation will stimulate the local melanin to gather in the local area during the recovery of these diseases, i.e. hyperpigmentation, which will make the patient suffer from the symptom of small black spots. 3. Hormone level disorders: if one stays up late for a long time or suffers from excessive mental pressure, the hormone level in the body will be disorganized, which will enhance the activity of melanin cells and secrete a large number of melanin particles, thus making the patient suffer from the symptom of long dark spots on the body. There may be other reasons for long black spots on the body, so it is recommended to go to regular hospitals in time and follow the advice of specialists to improve the examination and clarify the cause of the disease, and then give targeted treatment.