There are physiologic and pathologic causes of darkened skin on the elbow. Common physiological reasons are not pay attention to hygiene, contact staining and so on; pathological reasons include: trauma, psoriasis, acanthosis nigricans and so on. 1. Physiological reasons: if you do not pay attention to personal hygiene, elbow cleaning is not in place, or fabric fading stained skin or long-term friction elbow cuticle, may cause elbow blackening. It is recommended to pay attention to personal hygiene, daily cleaning of the skin, you can use mild exfoliating products to improve. 2. Trauma: due to elbow trauma, bumping local scabs, scabs fall off after the local is still in the recovery period, the elbow will appear pigmentation, resulting in elbow blackening. 3. Psoriasis: it is an inflammatory skin disease, which will be manifested as inflammatory red papules in the early stage of the disease, and then it will gradually expand or merge to become brown plaques, and the elbows will be blackened in the elbow area. 4. Acanthosis nigricans: mostly seen in obese patients, can be manifested as the skin joints or skin folds of the phenomenon of melanin deepening, hyperkeratosis, and then manifested as the elbow skin black. It can be seen that if it is caused by pathological reasons, the elbow skin black, it is recommended to go to the hospital in time to see a doctor, clear cause of the symptomatic treatment.