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An embolism is a foreign body, such as a blood clot or an air bubble, that travels through the bloodstream and becomes lodged in a blood vessel, blocking the flow of blood.

To function properly, the body’s tissues and organs need oxygen, which is transported around the body in the bloodstream. However, if an embolism blocks the blood supply to a major organ, such as the brain, heart or lungs, the organ will fail (lose some or all of its ability to function).

Two of the most serious conditions that can be caused by an embolism are:

  • stroke – the supply of blood to the brain is interrupted or completely cut off
  • pulmonary embolism – the blood supply to the lungs is cut off

How common are embolisms?

Embolisms are a common health problem and a major cause of disability and death in England and across the world. For example, in England each year it's estimated that:

  • 120,000 strokes are caused by embolisms, resulting in around 34,700 deaths
  • 37,000 pulmonary embolisms result in around 3,000 deaths

Risk factors

Risk factors for developing an embolism include:

Foreign bodies

A foreign body is any object or substance that shouldn't be present in your blood. Below are some examples of foreign bodies that can cause embolisms.

Blood clots

Blood contains natural clotting agents that help prevent excessive bleeding when you cut yourself. After a wound stops bleeding, the blood clotting agents dissolve the clot.

Certain health conditions, such as high blood pressure or heart disease, can cause blood clots (a thrombosis) to form even where there's no bleeding.

For example, a heart condition called atrial fibrillation, which is where the heart beats irregularly and abnormally fast, can cause a blood clot to form in the heart. If the blood clot breaks off it can travel in the bloodstream (known as an embolus) before being deposited in an organ or a limb.

See the A-Z topic about Thrombosis for more information about blood clots.


A fracture to a long bone, such as a thigh bone, can result in fat particles within the bone being released into the bloodstream. These are known as fat embolisms. They can also sometimes develop following severe burns or as a complication of bone surgery.


Embolisms can also occur if air bubbles or other gases enter the bloodstream.

Air embolisms are a particular concern for scuba divers. If a diver swims to the surface too quickly, the change in pressure can cause nitrogen bubbles to develop in their bloodstream. This can cause decompression sickness which is often referred to as ‘the bends’ (see below).

The A-Z topic about Air embolism also has more advice and information about this type of embolism.


In people who have extensive atherosclerosis (narrowed arteries due to a build-up of cholesterol), small pieces of cholesterol can sometimes break away from the side of a blood vessel, resulting in an embolism.

See the A-Z topics about Atherosclerosis and Cholesterol for more information.

Treating embolisms

How an embolism is treated will depend on:

  • what type of embolism it is
  • the size of the embolism
  • where in the body the embolism lies

Serious obstructions, such as pulmonary embolisms (see box, left) require emergency medical treatment.

An embolectomy is the surgical procedure to remove an embolism. During surgery, the surgeon will make a cut in the affected artery and the embolism will be sucked out. This process is known as aspiration.

Medication may be used to dissolve more serious embolisms that are caused by blood clots. Anticoagulant medication, such as warfarin and low-dose aspirin, can help to thin the blood and stop further clots forming. If you have a heart condition, you may also be prescribed an anticoagulant to help prevent clots forming.

Embolisms that are caused by air bubbles are usually treated in a hyperbaric chamber. Inside the chamber, the air pressure is higher than the normal air pressure outside, which helps reduce the size of the air bubbles inside the diver’s body.

As the air bubbles are mainly made up of nitrogen, if you have the bends you may also be given pure oxygen to breathe in order to force the nitrogen out of your body.


It's not possible to prevent all cases of embolism, but you can take steps to significantly reduce your risk. These steps include:

  • eating a low-fat, high-fibre diet that includes whole grains and plenty of fresh fruit and vegetables (at least five portions a day)
  • limiting the amount of salt in your diet to no more than 6g (0.2oz or 1 teaspoon) a day
  • losing weight if you're overweight or obese, using a combination of regular exercise and a calorie-controlled diet
  • giving up smoking if you smoke
  • exercising for a minimum of 30 minutes a day, five times a week

The bends

The bends, also known as decompression sickness, is where air bubbles become trapped in the bloodstream and block the flow of blood to the small blood vessels of the brain. This causes pain and paralysis (an inability to move).

The bends can sometimes affect scuba divers who surface too quickly because the pressure changes can cause nitrogen bubbles to form in the bloodstream (see main text for how the bends is treated).

Types of embolism

Three types of embolism are briefly described below.

Cerebral embolisms: these are caused when a foreign body, usually a blood clot, blocks the blood supply to the brain. Cerebral embolisms are the leading cause of stroke.

Pulmonary embolisms: these occur when a foreign body, usually a blood clot, blocks the blood supply to the lungs. Deep vein thrombosis (a blood clot in one of the deep veins in the leg) is a major risk factor for pulmonary embolism as the clot can travel up the leg to the lungs.

Amniotic fluid embolisms: amniotic fluid surrounds and protects a baby inside the womb. The fluid is separated from the mother’s blood by a sac that seals it inside the womb. Very rarely during labour, amniotic fluid can leak out of the womb and into the mother’s blood vessels, blocking them. The mother may then develop breathing problems, a drop in blood pressure and loss of consciousness.

See the Lifestyle & Wellbeing pages listed below for useful lifestyle information and advice.

Healthy eating


Physical activity

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