The causes of swelling are as follows: 1. It may be caused by local soft tissue contusion or fracture, resulting in rupture and bleeding of capillaries in subcutaneous or muscular tissues, resulting in local swelling. The swelling is usually accompanied by pain and subcutaneous petechiae in addition to swelling. 2. 4. It may be caused by degenerative diseases of the elderly, such as heart failure, renal failure or generalized hypoproteinemia, etc., which may lead to sunken swelling of both lower limbs or even the whole body.