Blood clots are among the most feared medical emergencies, and for good reason. They can lead to heart attacks, strokes and death. But not all clots are dangerous. In fact, clotting is a natural and often lifesaving bodily function that helps stop bleeding when we’re injured. It’s how a scraped knee stops oozing and why a minor cut doesn’t require a trip to the emergency room.

The danger arises when clots form in the wrong place or at the wrong time. Here’s what blood clots are, how they’re typically treated and what they actually feel and look like so you can know when it's time to worry.

What is a blood clot?

A blood clot is a gel-like clump of blood components, primarily made up of platelets and fibrin, that forms to stop bleeding. “Fibrin is a protein that forms a mesh-like structure to trap blood cells, and platelets are small cell fragments that clump together and adhere to the mesh,” explains Dr. Fadi Shamoun, a cardiologist and vascular medicine specialist at Mayo Clinic.

Clots are meant to form when the body signals for clotting in response to an injury, and then dissolve once healing begins. But not all clots form for the right reasons or in the right places. If a clot develops inside a blood vessel without external trauma, or if one forms appropriately but doesn’t dissolve, it can pose serious health risks.

Clots can form in either arteries (arterial thrombosis) or veins (venous thromboembolism, or VTE). “When clots form in the veins of the body’s circulatory system, they often develop in the legs and can travel to the lungs, causing what’s known as a pulmonary embolism,” says Dr. Shaline Rao, a cardiologist at NYU Langone Hospital, Long Island. Clots that form in arteries, she adds, can cut off blood flow to the heart or brain, leading to a heart attack or stroke.

“Low movement of blood can trigger clotting,” Rao explains. This can happen due to prolonged immobility, recent surgery, smoking, cancer, hormone therapy, pregnancy, or inherited clotting disorders. Underlying medical conditions like atrial fibrillation also increase the risk and age can be another factor. This is because our blood tends to clot more easily as we get older and blood vessel walls become more prone to damage.

What does a blood clot feel like?

What a blood clot feels or looks like depends on where it forms. For example, deep vein thrombosis (DVT), which occurs in the legs, may cause a heavy or cramping sensation – typically in just one leg – as well as localized swelling (especially below the knee), tenderness that worsens when walking or standing, a visible lump or cord under the skin and warmth or redness in the area.

If a clot travels to the lungs or heart, it can produce symptoms similar to a heart attack. These include sudden shortness of breath, nausea, sweating, sharp chest pain, a rapid heartbeat and “difficulty breathing, painful coughing and sometimes feeling lightheaded or faint,” Shamoun says.

Clots that form in the brain cause stroke-like symptoms, including “vision changes, slurring of speech, sudden weakness on one side of the body or even confusion,” says Dr. Doris Chan, a cardiologist at NYU Langone Hospital in Brooklyn.

While some clots produce dramatic symptoms, others are more subtle. That’s why unexplained swelling, pain, chest discomfort, or shortness of breath should always prompt immediate medical attention.

How are blood clots treated?

When a blood clot is suspected, imaging tools such as an ultrasound or CT scans are typically used to confirm the diagnosis and start treatment.

The most common treatment for vein-related clots is anticoagulation, which is often referred to as blood thinning. This type of treatment “prevents the clot from growing and reduces the risk of new clots,” Shamoun says. Common blood thinners include warfarin, heparin, apixaban, rivaroxaban and dabigatran.

Clots in arteries are usually treated with antiplatelet agents such as aspirin or clopidogrel, says Chan.

In more serious or high-risk cases, such as with strokes or pulmonary embolisms, patients may require more intensive clot-busting medications or minimally invasive procedures to remove the clot directly. “And some hospitals are equipped with devices that can suction out clots or use tools to reopen blocked arteries or veins,” Chan adds.

Supportive therapies like compression stockings are often also recommended, especially for patients with ongoing risk factors such as cancer or heart disease.

Regardless of what treatment plan is recommended, identifying the root cause of the clot is key. Early detection and proper care can prevent nearly every blood clot from becoming an emergency. “The best advice is if something feels off about your body,” suggests Rao, “it’s best to be seen by a doctor quickly to have all treatment options considered.”

This article originally appeared on USA TODAY: What blood clots actually feel and look like – and when to worry

Reporting by Daryl Austin, USA TODAY / USA TODAY

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