Blood clots can form in the deep veins (veins below the surface that are not visible through the skin) of your legs during travel because you are sitting still in a confined space for long periods of time. The longer you are immobile, the greater is your risk of developing a blood clot.

During a flight, your legs undergo several physiological changes primarily due to prolonged immobility and the unique cabin environment. Because you are sitting for hours in a cramped space, the "calf muscle pump"—which normally helps push blood back up toward the heart—is inactive. This causes blood to pool in the lower legs, often leading to swelling (edema) in the ankles and feet. In more serious cases, particularly on flights longer than 8 to 10 hours, this pooling increases the risk of Deep Vein Thrombosis (DVT), where a blood clot forms in a deep vein. The low humidity in the cabin can also cause dehydration, which thickens the blood and further heightens the risk of clotting. To mitigate these effects in 2026, travelers are advised to perform seated leg exercises, wear compression stockings, and walk the aisle every few hours to stimulate circulation and prevent the heavy, stiff sensation common after long-haul journeys.