context: Ever get a paper cut or nick yourself while shaving? When that happens, a blood clot saves the day. It quickly stops the bleeding, and when it's done its job, it usually breaks up. Sometimes, though, things can go wrong. When blood clots don't fall apart, they can be dangerous and lead to serious medical conditions. You can get them in blood vessels in just about any part of your body. They're most likely to affect a leg, especially if you sit for long periods of time. You might get a clot in your arteries, which carry oxygen in your blood from your heart to all the cells of your body. The result can be really serious. It can keep oxygen from getting to your heart, lungs, or brain, and cause a life-threatening emergency, like a heart attack or stroke. You could also get a clot in the veins that carry blood back to your heart. When that happens, symptoms usually come on more gradually, but can still mean trouble. If you learn the warning signs, you'll know when to get quick medical help that can make a huge difference in keeping you out of the danger zone. See More: Dos and Don'ts of a Blood Clot When a blood clot forms in one of the deep veins in your arm or leg, way beneath your skin's surface, it could be something called a deep vein thrombosis ( DVT). That's dangerous because the clot could travel to your heart or lungs. You're more likely to get a DVT if you've haven't moved around for a long time, say after surgery or during a long plane trip. Get medical help right away if you notice any of these symptoms: Swelling. This can happen in the exact spot where the blood clot forms, or your entire leg or arm could puff up. Change in color. You might notice that your arm or leg takes on a red or blue tinge, or gets warm or itchy. Pain. As the clot gets worse, you may hurt or get sore. The feeling can range from a dull ache to intense pain. Trouble breathing. If this happens, it could mean that the clot has moved from your arm or leg to your lungs. You may also get a bad cough, and might even cough up blood. You may get pain in your chest or feel dizzy. Call 911 to get medical help right away. Lower leg cramp: If the clot is in your calf or lower leg, you may feel like you have a cramp or charley horse. A blood clot that forms in or around your ticker may cause a heart attack. Watch out for symptoms like these: Severe pain in your chest and arm Sweating Trouble breathing A blood clot in your lung usually starts out in a deep vein in your arm or leg, then breaks off and travels to your lung. When this happens, you get what's called a pulmonary embolism, an extremely dangerous condition. Get medical help right away if you: Feel short of breath or have problems breathing Get pain in your chest Start to cough Begin to sweat Feel dizzy Blood clots here may be caused by fatty deposits in the walls of the blood vessels that bring blood to your brain. Or sometimes, they may form because of a blow to your head that leads to a concussion. In other cases, a clot that starts out in a different part of your body, like your chest or neck, might enter your bloodstream and travel to your brain, where it can cause a stroke. Watch out for these symptoms: Problems with your vision or speech A seizure General feeling of weakness Blood clots can happen in the veins that drain blood from your intestines. They can be caused by conditions like diverticulitis or liver disease, or even by birth control pills. How will you know if this is going on? Check with your doctor if you have problems like these: Nausea or vomiting Severe pain in your belly, which may be worse after you eat Diarrhea Bloody stools A sensation that feels like you're bloated A blood clot there can keep them from removing waste from your body. That can cause high blood pressure or even kidney failure. This is dangerous, so look out for these symptoms: Pain in the side of your belly, legs, or thighs Blood in your urine Fever Nausea or vomiting High blood pressure Sudden severe leg swelling Trouble breathing