Have you heard of deep vein thrombosis? Also known as DVT, this condition occurs when dangerous blood clots form in veins. Those blood clots can lead to a pulmonary embolism, which is potentially fatal. According to the University of Washington Medical Center, sitting for long periods of time can increase the risk for DVT, and so can constrictive clothing: "Avoid tight clothing, nylons, or socks (especially the type that are too tight at the top and/or leave marks on your skin) that might restrict blood flow through veins." Compression socks are a good choice for travelers interested in taking further steps to reduce the likelihood of DVT.