A purple bruise on the thigh means that there is subcutaneous bleeding on the thigh, which means that blood is leaking out of the blood vessels to the outside of the blood vessels. There are various reasons for purple bruises on the thighs: first, purple bruises occur after trauma to the thighs due to capillary rupture and extravasation of blood. Second, thrombocytopenia disease, because platelets are the blood cells responsible for hemostasis, the number of human hemostatic function will be reduced, sometimes in the absence of trauma will also occur bleeding, resulting in purple bruises on the thigh. Third, vitamin C deficiency, because vitamin C can increase the density of blood vessels, reduce the permeability of blood vessels, vitamin C deficiency will occur in the human body bleeding symptoms, prone to purple bruises on the thighs. Finally, coagulation disorders, such as hemophilia A, hemophilia B, vitamin K deficiency and other diseases, can also appear purple bruises on the thighs due to coagulation disorders.