context: Blood clots are jelly-like masses of blood. They can occur in arteries or veins in your heart, brain, lungs, abdomen, arms, and legs. You need your blood to clot when you're cut or injured. It helps stop bleeding. Most of the time, your body breaks down the clot after your wound has healed. But sometimes, they don't dissolve on their own. Other times, clots form inside your blood vessels for no reason. When this happens, it can lead to serious health problems. There are two main types of clots: Thrombus: Blood clots can be stationary. That means they don't move. But they can block blood flow. Doctors call this type of clot a thrombosis. Embolus : Blood clots can also break loose. Doctors call these embolisms. They're dangerous because they can travel to other parts of the body Clots are also classified by where they form. These form in your arteries -- the blood vessels that carry blood away from your heart. Arterial clots block blood and oxygen from reaching your vital organs. They can lead to tissue damage. Often, they occur in your legs and feet. Sometimes, they happen in your brain, where they can lead to stroke. Or, they may form in your heart, where they can cause a heart attack. Arterial clots can also take root in your kidneys, intestines, or eyes, though this is rare. Symptoms You may not have any at first. As the clot grows or blocks more of your blood flow, you might notice any of the following: Cold arm or leg Fingers or hands that feel cool to the touch Muscle pain or spasm in the affected area Numbness or tingling in your arm or leg Weakness of the affected limb Loss of color in the affected limb These form in your veins. They tend to develop slowly. That's why you might not know you have one until it causes problems. There are three types of blood clots that form in the veins -- superficial venous thrombosis, deep vein thrombosis ( DVT), and pulmonary embolism ( PE): Superficial venous thrombosis. This is a blood clot that forms in a vein close to the surface of the skin. They don't normally break loose and travel through the bloodstream. But they can be painful and need treatment. DVT, or deep vein thrombosis. This is also called a âvenous thrombosis.â It's a blood clot that forms in a major vein deep in your body. It usually happens in your lower leg, thigh, or pelvis. But it can also form in other parts of your body, like your arm, brain, intestines, liver, or kidney. Pulmonary embolism . This type of blood clot is a medical emergency. It's a DVT that breaks off and travels up your leg to your lungs, where it gets stuck. It can be fatal. Symptoms If your vein is near your skin's surface (superficial venous thrombosis), these may include: Painful, swollen, inflamed skin over the affected vein A vein that feels hard or painfully tender to the touch Red skin over the affected vein If you have a DVT, you may notice the following: The affected leg is swollen (sometimes both legs swell). You have a cramping pain or soreness in your leg, usually in the calf. It may be worse when you bend your foot back toward your knee. There's an aching, heavy feeling in the affected leg. The skin in the area of the clot is warm or red. A DVT is a medical emergency. See your doctor right away if you notice these symptoms. Left untreated, a DVT can turn into a pulmonary embolism. Call 911 if you have pain, swelling, or tenderness in your leg, and: You can't breathe. You have chest pain.