Leg and foot swelling during air travel is common and typically harmless. The most likely culprit is inactivity during a flight. Sitting with your feet on the floor for a long period causes blood to pool in your leg veins. The position of your legs when you are seated also increases pressure in your leg veins. This contributes to foot swelling by causing fluid to leave the blood and move into the surrounding soft tissues.

To relieve foot swelling during a flight:

• Wear loosefitting clothing
• Take a short walk every hour or so
• Flex and extend your ankles and knees frequently while you're seated
• Flex your calf muscles
• Shift your position in your seat as much as possible, being careful to avoid crossing your legs
• Drink plenty of fluids to prevent dehydration
• Avoid alcohol and sedatives, which could make you too sleepy or unsteady to walk around the cabin

Foot swelling isn't a serious problem if it lasts only a short time. But excessive swelling that persists for several hours after you resume activity may be due to a more serious condition, such as a blood clot in the leg (deep vein thrombosis) — especially if the swelling occurs in only one leg and is accompanied by leg pain. If you experience these signs and symptoms, seek prompt medical attention.

If you're at increased risk of blood clots — because you recently had major surgery or you take birth control pills, for example — consult your doctor before flying. He or she may recommend wearing compression stockings during your flight. In some cases, the doctor may prescribe a blood-thinning medication to be taken before departure.

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Sept. 17, 2016 See more Expert Answers