A bruise on the thigh indicates a subcutaneous bleeding condition on the thigh. This is because the red blood cells are leaking from inside the blood vessels to outside the blood vessels, which can cause the bruised thighs. In clinical practice, if a woman of childbearing age has a bruise on her thighs, the first thing to rule out is a condition called simple purpura. This disease is common in women of childbearing age, and the cause is related to changes in estrogen concentration in the body. The results of routine blood tests and coagulation tests are normal, and in this case, you only need to take vitamin C treatment. At the same time, if the thighs are blue and purple, vascular and platelet factors causing bleeding disorders, such as vitamin C deficiency, should be excluded. The bruising will occur when the capillaries become more permeable and the density decreases. Also, when thrombocytopenia occurs, the thighs may appear blue and purple. The causes of these diseases need to be identified and then treated differently for the cause.