There are several reasons a person's foot, ankle or leg could be swollen and red, ranging from a sprain of the ligaments to deep vein thrombosis. Each cause varies in severity, with some, such as deep vein thrombosis, needing emergency medical treatment, states Healthline.
A swollen ankle or leg could be caused by an ankle sprain. This happens when a person twists the ligaments in the ankle, causing them to swell and bruise. Another cause of red and swollen legs, ankles or feet includes Lou Gehrig's disease, which can cause the loss of muscle movement in the area, resulting in fluids gathering from a lack of movement, according to Healthline.
When the body cannot eliminate fluids properly, a person may experience edema, or the gathering of fluids, around the joints. Kidney failure may cause swelling in the legs and ankles due to the insufficient elimination of toxins from the body. Lymphatic obstructions, known as lymphedema, may also result in the swelling of the legs, explains Healthline. The swelling is the primary symptom of this condition, which is usually caused by surgery or cancer treatments.
An unusual cause of leg swelling could include osteomyelitis, which is better explained as a bone infection. This happens when the bones are invaded by fungi or bacteria. Swelling of the surrounding tissues is common and can be a major symptom of this condition, notes Healthline.