7 Blood Clot Symptoms You Should Never Ignore

You might have to whip out the measuring tape.

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You know the spiel: If you're on the Pill, you're at a higher risk for blood clots. If you fly for more than four hours, you're at a higher risk for blood clots. If you smoke at all, you're at a higher risk for blood clots.

But uh, what are blood clots—and what are the blood clot symptoms you should look out for?

Basically, blood clots occur when blood thickens, forming semi-solid clumps. Most of the time, clots are harmless and simply occur to stop the body from bleeding too much (like when you get a cut). However, when blood clots form in certain areas of your body—like your heart or lunges—they can cause serious issues.

When a clot forms in a vein, it’s known as deep vein thrombosis (DVT). Usually, DVT appears in the legs, but can show up in the arms after a serious upper-body injury, according to the National Institutes of Health.

These DVT clots often dissolve on their own, but can be life-threatening if they travel elsewhere in your body—like to the lungs (a.k.a. a pulmonary embolism), or to the heart where it can cause a stroke or heart attack.

But here's the thing: Blood clots aren't always easily spotted—they can feel like a slight discomfort in your arm or leg, if anything at all, says Patricia Vassallo, M.D., an assistant professor of cardiology at Northwestern University. Keep these common blood clot symptoms in mind—and if you think you could have one, head to the emergency room ASAP.

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1. You have swelling in one arm or leg.

DVT causes one leg to look puffier than the other, most often below the knee. “That’s because when a clot forms in your vein, blood can’t get back to your heart, and the pressure causes fluid to spread to the tissue in your leg,” explains Vassallo.

Your leg will likely be noticeably bigger, but if you're not sure, whip out the measuring tape. According to Vassallo, a leg with a clot will actually measure larger.

2. Your leg or arm is red and warm to the touch.

Reduced blood flow from a limb back to the heart increases pressure in a vein, pushing fluids into your other tissues and causing inflammation, warmth, and redness, says Vassallo.

Your whole leg usually appears red, although discoloration might look patchy, but keep in mind: “you can have a clot without redness or swelling,” says Vassallo.

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3. Your heart is racing and you're short of breath.

A racing heart is the most common—and sometimes the only—symptom of a pulmonary embolism (PE) when the clot has traveled to your lung. “It feels like you’ve exercised when you haven’t,” says Vassallo.

To compensate for the clot clogging up your lungs, your heart does actually beat faster to get more oxygen pumped to your body. When your doctor checks, your heart rate will be greater than 100 beats per minute when it’s normally in the 60 to 100 beats-per-minute range, says Vassallo.

4. You have pain in one of your legs or arms.

Uncomfortable pressure in your leg is another common blood clot symptom, due to inflammation. It usually isn’t severe, but it will feel painful, like something’s not right—especially when you’re walking, says Vassallo.

Most often, the pain gets worse with time (unless, of course, the clot resolves on its own). “What starts as a little cramping and soreness can become throbbing because the clot is getting bigger,” she adds.

5. You feel like you're having a panic attack.

It’s not uncommon to feel super anxious if you’re experiencing a PE. In addition to lightheadedness and dizziness, “it’s often a sense of impending doom, like you’re going to die,” says Vassallo.

That can sound very similar to a panic attack—which is actually a very common misdiagnosis among women under 40. Be sure to explain any other symptoms you’re experiencing along with your risk factors to your doctor.

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6. You have a sharp pain in your chest

In some cases of PE, you might feel chest pain that’s sharp, sudden, and hurts more if you take a deep breath or cough, says Vassallo.

Important to note: This feeling is different than chest pain caused by a heart attack, which is more of a dull ache or pressure, like an elephant is sitting on your chest.

7. You're coughing up blood.

A clot can result in inflammation and fluid buildup in your lungs, causing you to cough up blood. “That also happens with pneumonia, but it’s usually due to inflammation from PE,” says Vassallo.

Illustrations by Amanda Becker

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