Blood clots can be a very useful mechanism within the body. When you get a paper cut or other minor injury, the blood eventually stops flowing because of blood clots at the site of the wound. The clot stops you from losing all of your blood through one small cut. When the blood within your veins forms a clot, however, this same mechanism that usually protects you can turn deadly instead. Blood clots in your veins can break off and travel to essential organs, causing a heart attack or stroke. Understanding the common causes of blood clots helps you know if you're at risk for this complication.


Pregnancy is a condition that comes with plenty of risks, including blood clots. The additional weight puts pressure on your pelvis, which compresses the blood vessels in your legs and pelvic area. Pregnancy also causes your blood to clot more quickly due to an increase in estrogen. This increase in estrogen is a useful adaptation during labor and birth, but can also cause dangerous blood clots to form during and after your pregnancy. This risk level is relatively small in most pregnant women, but it increases when other risk factors for blood clots are present. To lower your chances, stay active and hydrated throughout your pregnancy.


Air Travel

Blood clots can occur during any prolonged period of inactivity, but flying is one of the most common culprits. Planes require passengers to sit for long periods of time without standing or walking around. Economy class seats have little leg room, so even stretching and flexing your feet and legs can be difficult for most passengers. In addition to this lack of movement, air travel is a common cause of dehydration, which increases the risk of blood clots as well. Drink lots of fluids and move around as much as possible, especially on longer flights or flights with especially constricting leg room.


Oral Contraception

Increased amounts of the hormone estrogen are among the biggest risk factors for blood clots. Oral contraceptives, also known as birth control pills, contain estrogen and other hormones that increase the risk of clotting. This risk is much higher for smokers than for regular users of birth control pills, as well as for those with a family history of blood-clotting issues. Many newer oral contraceptives, such as the mini-pill, only include progestin to reduce the chances of a clotting problem. However, it is still critical to avoid smoking while using oral contraceptives to keep this risk as low as possible.



You are at an increased risk for blood clots when your body becomes dehydrated. Most often, dehydration happens when you exert a lot of energy, don't drink enough fluids or are exposed to heat. When you become dehydrated, your blood vessels narrow, and your blood itself becomes thicker. This can have an adverse effect, and the potential for a blood clot to form increases. The risk is even greater when paired with other factors, such as inactivity or smoking. To avoid this scenario, make sure to drink fluids, especially if you know you'll be in warm environments or will be exerting yourself.


Cancer and Cancer Treatments

Cancer patients are more likely to develop blood clots than the average person, especially during treatment. Both cancer and its treatments may increase the blood's clotting ability, which can be dangerous for patients. Also, cancer patients are likely to have long periods of inactivity, such as during chemotherapy treatments or while on bed rest. This combination of risk factors can make blood clots more likely to form. Although there is little that can be done to decrease the risk for cancer patients, it is crucial to monitor signs and symptoms of pain or to swell in the leg or arm and to seek treatment as quickly as possible.



Blood clots are a bigger risk for people who suffer from obesity. Individuals who are obese carry extra fat, which slows down blood flow and puts more pressure on veins. Obesity also tends to coincide with an inactive lifestyle, which is another risk factor for blood clots. Finally, people with diabetes are more likely to have blood clots, and obesity is one of the leading causes of diabetes. To reduce obesity and the increased risk of blood clots, you should practice healthy behaviors in regard to diet and exercise.


Varicose Veins

Varicose veins are close to the surface of the leg and are primarily a cosmetic issue for most sufferers of this condition. However, they can also increase the risk of superficial thrombophlebitis, which is a blood clot in a superficial vein. Varicose veins occur when valves within the veins stop functioning properly, and blood is allowed to flow backward through the vein rather than flowing towards the heart. This can lead to blood clots in the shallow veins, which are often very painful. To prevent this from occurring, you should avoid extended periods of inactivity in which you do not move your legs.



Smoking is one of the most preventable causes of blood clots. People who smoke are more likely to get blood clots than non-smokers. This is especially true for those with another risk factor, like pregnancy, oral contraceptive use or a family history of clotting issues. Over time, smoking damages the lining of your blood vessels. This can lead to blood clots, along with plenty of other heart problems. If you currently smoke and are worried about the risk of blood clots, you should consider joining a smoking cessation program to help you quit.


Irregular Heartbeat

If your heartbeat is irregular, you may be at a higher risk of blood clots. Atrial fibrillation is a common cause of clots, and people who have this condition are often unaware of how serious it can be. With an irregular heartbeat, the blood is not pumped as efficiently as it would be in someone with a regular heartbeat. Consequently, blood may become stagnant, which triggers clotting mechanisms. This is an especially dangerous cause of blood clots, as clots that form in the heart are at risk of breaking off and flowing directly to the brain, causing a stroke. It is important to take your irregular heartbeat seriously and consult with your doctor about whether preventative treatment for blood clots may be necessary.



Patients who undergo surgery are at an increased risk of blood clots. There are two primary causes for this. First, surgery often coincides with prolonged periods of inactivity. This means that the blood flow in your body slows down, which can make clotting more likely. In addition, blood thickens when it comes into contact with foreign material, which occurs during surgery. The combination of these two factors can lead to blood clots in deep veins, which are particularly dangerous. During recovery, patients who have had surgery should try to move their body regularly to reduce the chance of blood clots.


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