My legs and feet swell in the summer, when I have been on my feet too long, and on airplanes.  This has been going on since I was in my forties and so far nothing I have tried has worked in the long term.  When I saw this article in the News Journal, I was intrigued and was hoping it would help me since I am about to fly to the UK.  This article came from the Mayo Clinic.

The official name for swelling edema and it is usually harmless when it occurs as a result of flying.  Inactivity is the main culprit, since sitting with your feet on the floor for extended periods of time can cause blood to pool in your leg veins.  The position of your legs when seated also increases pressure and contributes to foot swelling by causing fluid to shift from the blood vessels to the surrounding soft tissues.  Since the problem is related to gravity and the position the body is in, it is called dependent edema.

This painless swelling can affect both legs and may include the calves or even the thighs.  But excessive swelling that persists for several hours after deboarding may be due to a more serious condition such as a blood clot in the leg which is also called deep vein thrombosis.  You should be concerned 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.

To avoid excessive swelling during a long flight, stretch your legs often and get up and walk as often as possible.  Wear loose fitting clothes and while in your seat, flex and extend your ankles and knees.