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8 common causes of blood clots

Certain risk factors increase your chance of developing a blood clot
Common causes of blood clots - a view of the isle in the middle of a plane

If you bleed—whether from a papercut or a surgery—your body will create a blood clot to stop you from losing too much blood. As your body heals, the blood clot will dissolve. However, sometimes blood clots can cause serious complications inside the body, like a pulmonary embolism or stroke.

Blood clots most commonly appear in legs, arms and lungs, and they can happen at any age. “If you have a blood clot, you may notice swelling and pain in the area of the blockage,” said Brandon Williamson, MD, clinical assistant professor at Texas A&M Family Medicine Residency at the Texas A&M College of Medicine, primary care physician at Texas A&M Health Family Care.

Although blood clots can be life-threatening, there are ways to help reduce your risk. Williamson shares some of the most common causes of blood clots and what you can do to prevent them.


Anyone traveling for more than four hours, whether by air, plane or train, can be at risk for developing a blood clot. “Move around and stretch your legs frequently when on long trips,” Williamson said. “If you cannot leave your seat, then extend your legs and flex your muscles. This will encourage blood flow.”

If you are traveling for an extended period of time and have other risk factors, speak with your primary care provider about what you can do to protect yourself.

Recent surgery

A blood clot is your body’s natural reaction to bleeding. When you cut your hand, your body will develop a blood clot to stop the bleeding. Through the same processes, your body may use a blood clot to stop the bleeding from a surgery.

“The best thing to do after surgery is closely follow instructions and start walking and moving as soon as your provider gives you the okay,” Williamson said. Once you are cleared by your provider, start walking and moving around to get the blood flowing.”


Obesity is often associated with immobility and unhealthy eating. “Being overweight is linked to a significant number of health issues,” Williamson said. “Losing weight can be hard, but it is one of the most important things you can do for your health. “

In addition to losing weight, people who are overweight can reduce their risk by remaining active. If you are overweight, your primary care provider can help you find ways to reduce your risk.

Birth control pills

Oral contraceptives do not cause blood clots, but they do increase the risk of blood clots. Birth control pills prevent pregnancy by tricking the body into thinking it is already pregnant. They do this by increasing hormones—estrogen and progesterone—that rise in the body during pregnancy. These hormones increase the risk of blood clots.

“If you have several risk factors that make you more likely to develop a blood clot, then your primary care provider can help you find a method of birth control that will minimize that risk,” Williamson said. “You have many great options of birth control that do not contain these hormones.”


Women are five times more likely to develop a blood clot during pregnancy, childbirth and up to three months after delivery than women who have not been pregnant. Women who are pregnant are more likely to develop a blood clot because the body’s estrogen levels are higher than normal. The body is also starting to prepare to lose blood during childbirth, so it will become more prone to clot to reduce the blood loss.

Similarly, women on bedrest after childbirth tend to be less mobile, which limits the blood flow throughout the body.


Blood clots are more common in people as they get older, especially over the age of 65. “I cannot reiterate the importance of finding a good primary care provider,” Williamson said. “They will work with you as you age to monitor your risk for things like blood clots. It is possible to age gracefully, and your provider can help you.”

Cancer diagnosis and treatment

“Cancer puts your body into a more inflammatory state, which can cause an increase in the body’s natural clotting processes,” Williamson said. “Also, certain chemotherapy drugs can increase the risk of blood clots.”

Your oncologist should be aware of your potential risk of blood clots. However, to be your best advocate, start an open discussion with your provider about your risks.

History of blood clots

If you had a previous blood clot or someone in your immediate family had a blood clot, you are at a higher risk. There are many conditions, some genetic and some not, that increase your risk of a blood clot.

“If you have a sudden, unexplained blood clot, then your provider may consider these conditions as a possibility,” Williamson said. “Be open and honest about your family history of blood clots. If you have one of these conditions, then your provider can put you on a treatment to reduce your risk.”

The bottom line

If you do develop a clot, your primary care provider may run a series of screening tests to determine the cause. “A blood clot often means something else is going on with your health,” Williamson said. “Communicate openly with your health care provider to evaluate your risk.”

Media contact: Dee Dee Grays,, 979.436.0611

Mary Leigh Meyer

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