The thighs of a piece of purple for no reason, may be trauma, thrombocytopenic purpura and contact dermatitis caused. Patients need to according to the specific situation, targeted treatment to improve the symptoms. 1, trauma: when the thigh area by the collision or extrusion, may lead to subcutaneous capillary rupture, the emergence of a piece of purple. Generally do not need to do too much treatment, less bleeding can be relieved by themselves; 2, thrombocytopenic purpura: a disease caused by the reduction of platelets in the body, may appear in the skin or mucous membrane parts of the bruises and bleeding phenomenon, manifested in the thighs of the blue piece of a purple piece for no reason. It can be relieved by plasma replacement, and platelets need to be imported if necessary; 3, contact dermatitis: when the skin of the thigh area is unintentionally in contact with irritating external substances, it may irritate the skin or cause allergies, forming contact dermatitis, which leads to thighs bruises and purple, and some patients may have local itching and blistering symptoms. Mometasone furoate cream can be applied locally for relief, and mupirocin ointment is also needed if bacterial infection occurs. During the recovery period, it is necessary to do a good job of local cleaning and hygiene, but also to avoid eating spicy, stimulating food.