Find Information About:

Drugs & Supplements

Get information and reviews on prescription drugs, over-the-counter medications, vitamins, and supplements. Search by name or medical condition.

Pill Identifier
WebMD

Pill Identifier

Having trouble identifying your pills?

Enter the shape, color, or imprint of your prescription or OTC drug. Our pill identification tool will display pictures that you can compare to your pill.

Get Started
My Medicine
WebMD

My Medicine

Save your medicine, check interactions, sign up for FDA alerts, create family profiles and more.

Get Started

WebMD Health Experts and Community

Talk to health experts and other people like you in WebMD's Communities. It's a safe forum where you can create or participate in support groups and discussions about health topics that interest you.

  • Second Opinion
    WebMD

    Second Opinion

    Read expert perspectives on popular health topics.

  • Community
    WebMD

    Community

    Connect with people like you, and get expert guidance on living a healthy life.

Got a health question? Get answers provided by leading organizations, doctors, and experts.

Get Answers

Sign up to receive WebMD's award-winning content delivered to your inbox.

Sign Up

Deep Vein Thrombosis Health Center

Font Size
A
A
A

Blood Clots

Blood has a seemingly impossible job: It must flow continuously and smoothly throughout your body for an entire lifetime, but quickly shut off to prevent spills when you get a cut or injury.

Blood clots are healthy and lifesaving when they stop bleeding. But they can also form when they aren't needed and cause a heart attack, stroke, or other serious medical problems.

Recommended Related to DVT (Deep Vein Thrombosis)

Is It DVT or Something Else?

If one of your legs is red, swollen, painful, or warm, get it checked out right away. A number of conditions can cause these symptoms. Some of them are harmless. Others are much more serious. Learn when it’s nothing serious and when you should get checked by a doctor.

Read the Is It DVT or Something Else? article > >

How Does Blood Clot?

The life cycle of a normal blood clot depends on a series of chemical interactions.

1. Platelets form a plug. Tiny bits in your blood called platelets get "turned on" by triggers released when a blood vessel is damaged. They stick to the walls in the area and each other, changing shape to form a plug that fills in the broken part to stop blood from leaking out.

When activated, platelets also release chemicals to attract more platelets and other cells, and to set off the next step.

2. The clot grows. Proteins in your blood called clotting factors signal each other to cause a rapid chain reaction. It ends with a dissolved substance in your blood turning into long strands of fibrin. These get tangled up with the platelets in the plug to create a net that traps even more platelets and cells. The clot becomes much tougher and more durable.

3. Reactions stop its growth. Other proteins offset extra clotting factor proteins so the clot doesn't spread farther than it needs to.

4. Your body slowly breaks it down. As the damaged tissue heals, you don't need the clot any more. The tough fibrin strands dissolve, and your blood takes back the platelets and cells of the clot.

What Causes Blood Clots?

The process begins whenever flowing blood comes into contact with specific substances in your skin or in blood vessel walls. When they touch, it usually means the skin or blood vessel wall is broken.

Waxy cholesterol plaques that form in arteries have these things inside, too. If the plaque breaks open, they'll start the clotting process. Most heart attacks and strokes happen when a plaque in your heart or brain suddenly bursts.

Blood clots can also form when your blood doesn't flow properly. If it pools in your blood vessels or heart, the platelets are more likely to stick together. Atrial fibrillation and deep vein thrombosis (DVT) are two conditions where slowly moving blood can cause clotting problems.

Today on WebMD

TAG dvt blood clot
Symptoms, causes, risk factors, and more.
businesswoman in airport
Tips to prevent another clot.
 
blood thinners
Tips for DVT.
Blood clots in artery
Causes and treatments.
 
Simple Steps to Lower Cholesterol
Slideshow
Having Surgery Tips To Reduce DVT Risk And More
Slideshow
 
New DVT Therapies On The Horizon
Video
Atrial Fibrillation Guide
Slideshow
 

WebMD Special Sections