If a person has edema of the foot on the left side, consider an abnormality in a unilateral limb. Most commonly, the most common inflammatory condition is cellulitis. Cellulitis is an infection of the subcutaneous tissue due to various causes. This infection is often accompanied by redness, swelling, heat, and pain of the skin, and the differential diagnosis can be made by the appearance of the skin. Conditions that rule out inflammation are likely to be traumatic, often with a clear history of trauma. If it is not trauma and not inflammation, it may be insect bites, and of course there may be allergies, which are often accompanied by red skin color or allergic conditions, such as itching or rash. If these conditions are ruled out, the swelling may be caused by gout nodules, which are associated with severe pain and may have abnormal uric acid in the blood. If all the above conditions are excluded, ultrasound of the urinary system or blood vessels of the lower extremities is needed to exclude thrombosis caused by certain diseases of the urinary system or, of course, by surgical diseases, which requires careful differential diagnosis.