Arm joints black is mainly caused by the skin long time friction, usually pigmentation, with the increase of time can gradually fade. If the black color is serious and does not come off easily, hydroquinone cream is given for external use. The elbow joint activity is big, the skin is loose, the skin horny layer is thicker, it is easy to be friction, most of them are caused by pigmentation, which is a normal phenomenon, if there is no uncomfortable symptom, then there is no need for special treatment, generally with the increase of time can be gradually faded. If necessary, hydroquinone cream and other local decolorizing drugs can be given externally. Normally, we should pay attention to protect the elbow joint and avoid frequent friction.