The thighs are bruised when touched, which is considered to be physiological phenomenon, purpura simplex and blood diseases. 1. Physiological phenomenon: the thigh area suffered a collision will cause some damage to the soft tissue, but also cause local capillary rupture bleeding, due to the thin skin, subcutaneous fat is less, there will be bruises. 2. Purpura simplex: the cause and pathogenesis of purpura simplex is not particularly clear, considering the relationship with capillary abnormalities, may also be related to hormones, mainly prone to skin ecchymosis or bruises. 3. Blood diseases: If you suffer from some blood diseases, such as hemophilia, leukemia, aplastic anemia, etc., it will lead to the patient’s poor coagulation mechanism, platelet count is reduced, after the collision of bleeding more, so there will be bruises. Thigh bruises, there may be other reasons, it is recommended to go to the hospital in a timely manner, by the doctor to clarify the cause of standardized treatment.