What causes my ankles to swell?

Q. I only get ankle swelling in the summer. Why is that? Is there any reason to worry about it?

A. New ankle swelling should prompt a call to your doctor. A person can retain fluid for many reasons, including kidney or liver problems, heart conditions, malnutrition, thyroid disorders, and anemia. One swollen ankle may be due to a blood clot or injury.

But the most common reason for swelling in both ankles is incompetent valves in the leg veins. The leg veins return blood to the heart after the blood has delivered its oxygen and nutrients to the foot and lower leg. Unlike arteries, veins can't rely on the pumping action of the heart to move blood in the right direction. To keep blood moving back to the heart, valves in leg veins prevent backflow. Many people have malfunctioning vein valves that cause backward pressure and fluid leakage, which can often result in varicose veins. You can decrease ankle swelling from incompetent valves in the veins by wearing support hose or compression calf sleeves favored by runners, and elevating your ankles above the level of your heart.

Another cause of ankle swelling is warm temperatures. The small blood vessels in the skin dilate to allow heat to escape, which helps keep body temperature from rising. But this also means more than the usual amount of fluid can leak into the surrounding tissues, especially in the legs. You can help prevent ankle swelling in warm weather by reducing your salt intake, which decreases water retention. A low-dose water pill (diuretic) also may be prescribed for people who need help to control swelling.

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