Blood Clots

Blood clots are semi-solid or gel-like masses that form in your arteries and veins. Blood clots help control bleeding, but they may also cause serious medical issues, including deep vein thrombosis, pulmonary embolism and heart attack.


What is a blood clot?

A blood clot is a semi-solid mass of blood cells and other substances that form in your blood vessels. Blood clots protect you from bleeding too much if you’re injured or have surgery. However, you may develop blood clots for other reasons, such as having certain medical conditions. When that happens, blood clots may cause symptoms and can be life-threatening.


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What do blood clots do?

Blood clots are the first line of defense if something damages your delicate blood vessels. If you cut yourself from shaving, blood clots are why the bleeding usually stops after a few seconds or minutes.

You can develop a blood clot for other reasons, such as being immobile for a long time or having medical conditions that increase your blood clot risk. When that happens, your blood doesn’t flow as it should.


What are blood clots made of?

Blood clots are made of platelets and fibrin. Platelets are small colorless fragments of cells that your bone marrow makes. Fibrin is a blood protein. It’s sticky and may look like long strings. Platelets and fibrin work together to seal injured areas of your blood vessels.


What do blood clots look like?

A blood clot may look like a clump of reddish jelly held in place with netting. A closer look at a blood clot may show cells that look like tiny plates. These are platelets. The netting is fibrin. Blood clots’ red color comes from red blood cells that are trapped in fibrin as they flow past the injured area.

Where are blood clots located?

You can have a blood clot anywhere in your body. Blood clots that happen in your veins may develop in your arms and legs. This is deep vein thrombosis (DVT). Blood clots that develop in your arteries may appear in your lungs. This is pulmonary embolism. Blood clots that block blood flow to your brain may cause a stroke. Blood clots in your heart may cause a heart attack.


When would I notice a blood clot?

In general, you’d notice blood clot symptoms from clots forming in your veins and arteries. Leg pain, swollen legs and change in skin color may be DVT symptoms. Chest pain or shortness of breath can be symptoms of blood clots in your lungs or heart.

Conditions and Disorders

What conditions or disorders involve blood clots?

Blood clot issues are associated with many different kinds of conditions. You may develop a blood clot because you cut yourself and your body is working to stop your bleeding. There are conditions that focus on blood clots, such as bleeding disorders or blood clotting issues. You may also develop conditions that increase your risk of developing blood clots.

Bleeding disorders

If you have a bleeding disorder, it means your blood doesn’t clot as it should and you’re at risk of bleeding uncontrollably if you’re injured. Bleeding disorders include:

  • Von Willebrand disease: Most people who have von Willebrand disease inherited a mutated gene from one of their biological parents. But von Willebrand disease is also a complication of cancer, autoimmune disorders and heart and blood vessel diseases.
  • Thrombocytopenia: You may develop thrombocytopenia if you have low platelet counts.
  • Inherited hemophilia: This condition happens because your body doesn’t make enough clotting proteins to help your blood form clots.

Blood clotting disorders

A blood clotting disorder (hypercoagulable state) is a condition that causes your body to make more blood clots than normal. People may inherit disorders that increase the risk of blood clots or develop disorders during their lifetime. Common blood clotting disorders include:

  • Factor V Leiden: This inherited disorder is the most common blood clotting disorder. It slightly increases your risk of deep vein thrombosis (DVT) or pulmonary embolism.
  • Prothrombin Gene Mutation: Like Factor V Leiden, this inherited condition slightly increases your risk of deep vein thrombosis or pulmonary embolism.
  • Antiphospholipid Syndrome: This autoimmune disorder increases blood clot risk.

What other factors increase blood clot risk?

Many factors may increase blood clot risk. For example, people with severe coronavirus disease 2019 (COVID-19) have an increased risk. Other factors include:

  • Age. People age 65 and older have increased blood clot risk.
  • Pregnancy.
  • Having obesity.
  • Having cancer.
  • Taking birth control pills or having hormone therapy.
  • Smoking.
  • Not being able to move around.


Can I prevent blood clots?

If you’re born with an inherited (genetic) form of blood clotting disorder, you can’t do anything to prevent the condition or blood clots that happen because of the condition. But you may reduce your risk of developing blood clots by:

  • Seeing a healthcare provider for an annual physical examination.
  • Participating in regular cancer screenings.
  • Staying at a healthy weight for you.
  • Not smoking.
  • Staying hydrated.
  • Considering non-estrogen alternatives for birth control or hormone therapy.
  • Staying active.

A note from Cleveland Clinic

Blood clots help control bleeding, whether you’re bleeding from a paper cut, a serious injury or even after surgery. On the other hand, blood clots can also be life-threatening if they keep blood from flowing through your body. Blood clots happen for many reasons, some of which you may not be able to avoid. For example, you may have an inherited (genetic) condition that increases your risk of developing blood clots. If that’s your situation, you’re probably managing your condition with medication and other steps. If you’re worried about developing blood clots, talk to a healthcare provider. They’ll evaluate your overall health and recommend ways you can reduce your risk of developing them.

Medically Reviewed

Last reviewed on 04/03/2023.

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