context: If one of your legs is red, swollen, painful, or warm, see a doctor right away. A number of conditions can cause these symptoms. Some of them are harmless, but others are much more serious. Learn the differences here. If a piece of the clot breaks off and travels to your lungs , it can cause a pulmonary embolism -- a blood clot in your lung. This can be deadly. You can get DVT at any age, and several things can cause it. Some of them are: Injury to a vein Bed rest Sitting for a long time, such as on a flight Birth control pills Hormone replacement therapy Pregnancy Chronic diseases like heart disease, lung disease, cancer, Crohn's disease, or ulcerative colitis Family history of DVT or pulmonary embolism Obesity A medical condition that increases your risk for blood clots DVT normally affects just one leg. Symptoms include: Unequal swelling, where one leg is larger than the other Pain or tenderness when you stand or walk Warmth Red or discolored skin About half of the people who get it won't have any signs. You may not know you have a clot unless a piece of it breaks off and travels to your lung. That's a medical emergency. Call 911 right away if you have: Shortness of breath Pain when you take a deep breath Coughing up blood Racing heart rate Rapid breathing This happens when a blood clot forms in a vein just under your skin. If you have it, you may have: Swelling Pain Tenderness Warmth Redness These symptoms are much like those for DVT, but the two conditions are different. DVT happens deep within your body. Superficial thrombophlebitis is close to the surface. About 20% of people who have superficial thrombophlebitis also get a blood clot in their leg . Call your doctor if you notice anything unusual. They'll be able to rule out a more serious problem. You get this when the arteries in your legs become hard and narrow. In PAD, plaque builds up in the arteries. Over time, it can block blood flow to your arms and legs. When this condition affects veins instead of arteries, it's called peripheral vascular disease ( PVD). It can cause DVT. Some of the symptoms are: Pain, numbness, aching, or heaviness in your legs when you walk Cramps in your feet, leg, or butt Sores or wounds on your feet or legs that don't get better Pale or bluish-colored skin One leg feels cooler than the other PAD isn't a medical emergency, but lack of blood flow to your legs can cause serious problems like gangrene. That's when the tissue in your leg dies. You'll also have a greater risk for heart disease , heart attack , and stroke . But when you make changes to manage your condition, you'll lower your chances of getting those, too. The same risks that lead to heart attacks and strokes also cause PAD. They include smoking , diabetes , high blood pressure , and high cholesterol . Unlike DVT, these appear just beneath the surface of your skin. You get them when the valves inside your veins become weak or damaged. Normally, the valves help blood flow to your heart . When they don't work right, blood pools inside your veins. They swell and become large and rope-like. That's another difference from DVT -- the surface-level clots that come with varicose veins don't usually break free and travel to your lungs. When DVTs do this, it's called a pulmonary embolism, and it can be fatal. If you have varicose veins, you'll notice: Swollen ankles and feet Throbbing or cramping in your legs Itchy lower legs or ankles Achy, painful legs Heaviness in your legs Varicose veins aren't serious. Talk to your doctor about treatments. These are a smaller type of varicose veins . They affect your capillaries, the smallest blood vessels in your body. You're most likely to get these on your legs or face. They look like a spider web or the branches on a tree. They're usually a blue or reddish color. You may not like how they look, but they don't cause any medical problems. And because they're like varicose veins, spider veins also differ from DVT because they're close to the surface and don't tend to break free and move into your lungs.