What You Should Know About Flying and Blood Clots

Medically Reviewed by Carol DerSarkissian, MD on August 30, 2022
4 min read

Delays, lost luggage, and trying to stay away from germs aren't the only things to think about when you fly. Long airplane trips can also raise your chances of getting blood clots.

A clot is a clump of blood that forms inside a vein or other blood vessel. Deep vein thrombosis (DVT) is when the clot is in a large vein deep inside your body, usually the lower leg or thigh. The clot can block the flow of blood through the vein.

If a clot breaks free, it can get stuck inside a blood vessel in your lungs. This is a pulmonary embolism (PE), and it can be dangerous.

Overall, your chance of getting a clot when you fly is low. But certain things -- like your weight and age -- can make you more likely to get one.

A few precautions before, during, and after your flight can help you avoid blood clots.

You can get a clot if you stay still for a long period of time. When you move, muscle contractions help to push blood through your veins back to your heart.

Sitting on a plane for many hours not only allows blood to pool, but it also puts your knees at an angle that makes the veins inside them kink up. Just as water doesn't flow easily through a kinked-up garden hose, blood can't flow as well through a vein that has a kink.

On top of that, changes in air pressure inside the airplane cabin cut down the amount of oxygen you breathe in. Low oxygen in your blood can also make blood clots more likely to form.

Obesity -- a body mass index (BMI) of 30 or higher -- is one of the biggest blood clot risks. The extra weight slows the flow of blood through your veins.

You may also have greater odds of getting blood clots on a flight if you:

Varicose veins can also raise your chances of blood clots. These bulging, thick veins have a faulty valve that allows blood to get stuck and pool inside them.

The clots that form in varicose veins are closer to the surface of your body than those that form in deep veins. They're not as dangerous because they don't often travel to the lungs and cause PE, but they can be uncomfortable.

Most people don't need to worry much about clots on short flights. But if you're already at risk for clots and you plan to take a plane trip that's longer than 6 hours, you can do a few things to avoid them.

Get up and walk around every 2 to 3 hours. If there isn't enough room to walk or the "fasten seatbelt" sign is on, do calf raises and other leg stretches at your seat every 30 minutes or so.

Drink water before and during the flight. The air you breathe inside a plane is often dry because the same air circulates around the cabin. When you're dehydrated, your blood gets thicker. Avoid coffee and alcohol, which can dry you out even more.

Breathe deeply or listen to relaxing music to help you sleep. Avoid sleeping pills, which prevent you from getting up and moving as much as you should.

Before you leave, talk to your doctor, especially if you've had blood clots on flights in the past. They might suggest that you wear compression stockings, which put gentle pressure on your legs to keep the blood flowing. You can find them online and at drugstores, or your doctor can have them custom-fitted for you.

If you're at very high risk for blood clots, you may need to go on a low-dose "blood thinner" medication before you leave.

Learn to recognize the symptoms of DVT and PE so you can get medical help if you need it.

DVT can cause:

  • Swelling in a leg
  • Pain or tenderness
  • Warmth and redness of the skin

If you develop PE, you can have symptoms like:

  • Shortness of breath
  • Fast or unsteady heartbeat
  • Chest pain that gets worse when you breathe deeply or cough
  • Dizziness or fainting

Blood thinners are the main treatment for DVT. They help dissolve the clot you have and stop new clots from forming. You might need to take them for 3 months or more.