The causes of thigh pain can be strains caused by strenuous exercise, varicose veins in the lower limbs, venous thrombosis in the lower limbs and so on. 1. Strain: If the patient suffers from trauma or does intense exercise that exceeds the load of the body, it is possible to cause muscle strain of the thigh, which is manifested as swelling and pain in the thigh and affects the ability to exercise. 2. Varicose veins: The cause of varicose veins is mainly due to the decreased elasticity of the blood vessels in the lower limbs, the blood accumulates in the leg veins for a long time, and the patients can observe that the blood vessels in their thighs become obvious or even protrude. If the blood is stagnant for a long time, it will cause pain and swelling in the thighs. 3. Lower extremity venous thrombosis: If the lower extremity venous thrombosis occurs, the veins will also have reflux obstacles, and the thighs will be painful and swollen, and the pain will be more intense compared to varicose veins. In addition to this, thigh pain can also be neurodermatitis, osteosarcoma, lumbar spine disease and so on. Therefore, if thigh pain is not relieved for a long time, you should go to the hospital immediately and choose the treatment according to the doctor’s advice.