Legs swell for a variety of reasons, not all of them medical. Mild swelling of the ankles and feet occurs in many people who stand a great deal, during hot spells or after long-haul flights. It is made worse by sloppy footwear and lack of exercise. Such swelling usually resolves overnight after the feet have been elevated to heart level.
Constant swelling of the ankles may represent a disorder in circulation, assuming it is not secondary to trauma or to known heart or kidney disease. The two most common circulatory abnormalities leading to swollen legs are venous disease and lymphatic disease.
The former may occur as a result of damage to the veins in the superficial or deep venous systems, as an inherited condition or secondary to deep venous thrombosis. Damage to superficial veins is usually curable. Deep venous damage is treatable, but if excessive usually requires lifelong management and support.
Lymphoedema caused by lymphatic disease is uncommon in the UK. When it occurs, it is often due to inherent damage to the lymphatic vessels. Obstruction of the vessels by lymph node damage is rare, and inherited familial lymphoedema (Millroy's disease) even more so. Leg swelling in lymphoedema is often exacerbated by repeated bouts of skin infections (cellulitis) or fungal infection (particularly Athlete's foot).
Treatment is usually non-surgical and is directed at controlling the swelling.