A bruise on the thigh means that there is bleeding under the skin of the thigh, which is the leakage of red blood cells from inside to outside the blood vessels, resulting in a bruise on the thigh. A bruise on the thigh can be caused by a variety of reasons, the most common being an unintentional bruise where a capillary ruptures under the action of an external force, resulting in a bruise on the thigh. It is also seen in a disease called simple purpura, especially in women of childbearing age, where bruising occurs without obvious trauma and tends to recur. Sometimes there is a mild painful sensation when pressing down, which sometimes brings some psychological stress to women of childbearing age. This disease is related to changes in the concentration of estrogen in the body and has no major effect on the body, and is treated well with vitamin C. In addition, patients with thrombocytopenia may also experience bruising on the thighs due to a decrease in the hemostatic function of platelets.