What are blood clots?

Your body’s arteries and veins are a superhighway system designed to transport oxygen-rich blood from your heart to the rest of your body. They then carry oxygen-depleted blood back from your body to your heart.

Normally, this system runs smoothly, but sometimes you can develop a bottleneck called a blood clot. Blood clots are solid clumps that form in the blood. They serve the useful purpose of preventing you from bleeding too much when you hurt yourself.

Sometimes, a blood clot can form inside an artery or a vein when you haven’t been injured. These types of clots can be dangerous because they can form a blockage. They’re especially dangerous if they break off and travel to your brain or lungs.

Learn where else blood clots can form, why they can be dangerous, and how to avoid getting them.

Blood clots can form in many different parts of the body. Sometimes, clots can break off and travel through the bloodstream from one body part to another.

Clots can be found in your:

Some clots form in small veins near the surface of the skin. Others develop in deeper veins.

When you get a cut that’s deep enough to pierce a blood vessel wall, blood cells called platelets rush to the opening. Proteins in the liquid part of your blood, or plasma, make the platelets stick to the hole. The proteins and platelets form a sticky plug that stops the blood from flowing out.

After your body heals the wound, it dissolves the clot.

You also can get blood clots if you have a disease that makes your body produce too many red blood cells (RBCs) or platelets.

This is also referred to as a “hypercoagulable state.” Other diseases can prevent your body from breaking down blood clots properly when you no longer need them. Damage to the heart or blood vessels can affect blood flow and make clots more likely to form.

You’re more likely to get blood clots if you have one of these conditions.


In atherosclerosis, or “hardening of the arteries,” a waxy substance called plaque builds up in your arteries. If the plaque bursts open, platelets rush to the scene to heal the injury, forming a blood clot.


Some types of cancer can lead to tissue damage or inflammatory responses that may activate blood clotting. Some cancer treatments (such as chemotherapies) can also increase your risk for blood clots. In addition, having surgery to remove a cancer can put you at risk.


People with diabetes are more likely to have plaque buildup in their arteries.

Family history of blood clots or an inherited blood-clotting disorder

A family history of blood clots or an inherited blood-clotting disorder (such as one that makes your blood clot more easily) can put you at risk for developing blood clots. Typically, this condition on its own will not cause blood clots unless combined with one or more other risk factors.

Heart failure

In heart failure, damage to the heart prevents it from pumping as efficiently as it should. Blood flow slows, and clots are more likely to form in the sluggish blood.


Being immobile, or not moving for a long period of time, is another risk factor. Immobility is common after surgery, but extended air travel or car travel can also lead to immobility.

When you’re immobile, your blood flow can slow down, which can cause your blood to clot.

If you’re traveling, stand up and move around regularly. If you’re going to have surgery, talk to your doctor about ways you can reduce your risk for blood clots.

Irregular heartbeat

If you have an irregular heartbeat, your heart beats in an uncoordinated way. This can cause blood to pool and form clots.


Pregnancy also increases your risk for blood clots.

As your pregnancy progresses, your growing uterus can compress your veins. That can slow down blood flow, especially to your legs. A decrease in blood flow to your legs can lead to deep vein thromboembolism (DVT), which is a serious form of blood clot.

Additionally, as your body prepares for delivery, your blood begins to clot more easily.

Clotting is important following childbirth as it will help prevent the loss of too much blood. However, this improved ability to clot can also increase your chances of blood clots prior to delivery. Moving around and staying hydrated can help prevent clots during pregnancy.

Unhealthy weight

People who are overweight or obese are more likely to have plaque in their arteries.


In vasculitis, blood vessels swell and become damaged. Clots can form in the injured areas.

Not everyone who has a blood clot will experience symptoms.

Any symptoms of a blood clot that you do experience will depend on where the clot is in your body.

Clot locationSymptomsOther information
legswelling, redness, pain, warmth, calf tendernessalso known as deep vein thrombosis (DVT)
armswelling, redness or bluish, cramping, warmth, arm tendernessalso known as deep vein thrombosis of the upper extremities (DVT-UE)
lung shortness of breath, chest pain that gets worse when you breathe, coughing, fast heartbeat, cough that might bring up bloody phlegmalso known as pulmonary embolism (PE)
heart chest pain or heaviness, shortness of breath, left arm numbness, lightheadedness, nausea, sweatingassociated with heart attack
brain trouble speaking, sudden and severe headache, loss of vision, dizziness, weakness in the face or limbsassociated with stroke
abdomensevere abdominal pain, vomiting, diarrheaalso known as abdominal blood clots

Clots that form in small veins usually aren’t very serious. Ones that form in deep veins can travel to other parts of your body and cause a life-threatening blockage.

  • A DVT is a clot that forms in a deep vein, usually in the leg.
  • Pulmonary embolism (PE) happens when a clot breaks off and travels to the lungs. PE can block blood flow in the lung and make it difficult to breathe.
  • A blood clot in your heart can cause a heart attack.
  • A clot that travels to your brain can cause a stroke.

Blood clots are a medical emergency. If you suspect you have a blood clot, you should contact your doctor or local emergency services immediately regarding treatment.

Blood thinners may be used to treat many different types of blood clots. Examples include warfarin (Coumadin) and apixaban (Eliquis), which belong to a group of blood thinners known as anticoagulants.

Clopidogrel (Plavix) is another commonly prescribed blood thinner. It’s an antiplatelet, so it works by preventing the platelets from forming blood clots.

Drugs called thrombolytics may be used if your blood clots are the result of a heart attack.

Some people with DVT and PE may have a filter placed inside their inferior vena cava(the vein that carries blood to the heart). This filter prevents clots from traveling to the lungs.

Mechanical clot removals, also known as mechanical thrombectomies, can be performed in the event of a stroke.

Follow these tips to avoid getting a blood clot:

  1. Don’t sit for long periods of time. If you’re on a long flight or stuck in bed after surgery, try to get up every hour or so to move around, if possible. Staying active will prevent blood from pooling in your legs and forming a clot.
  2. If you’re overweight, try to lose weight. People who are overweight are at greater risk for plaque in the arteries that leads to blood clots.
  3. Control diabetes and heart disease. These conditions can increase blood clot risk.
  4. Don’t smoke.The chemicals in cigarettes damage blood vessels and make platelets more likely to clump together.
  5. Drink a lot of water. Having too little fluid in your body makes your blood thicker.

If you’re concerned about your risk for blood clots or would like more information, speak with your doctor.