Inactivity for longer duration often cause DVT, as it decreases the circulation of blood in the body especially in lower parts of the body. The circulation of blood in the body is regulated by the movement. If the movement is stopped then blood circulation slows down and thus the chances of clot formation in lower legs are increased. Prolonged immobility due to traveling or sitting for long hours in car or train or bed rest due to any illness may lead to DVT. Sometimes old age is also responsible for the inactivity making older people prone to the disease.

Hospitalization for long durations makes you inactive especially in case of surgeries and it raises your probability of getting a blood clot. The chances of deep vein thrombosis are more in some of the major surgeries like hip replacement surgery and surgeries on chest, knee, calf, and leg. After surgery, proteins, fats, and tissue debris proceed into the veins, which also release a substance that enhances the clotting of blood. The long rest after surgery makes you more prone to DVT.

Pregnancy is another factor that enhances the chances of blood clotting. In case of C-section, the chances are even more. Various tests are conducted during and after pregnancy to reduce the risk of DVT. The danger of deep vein thrombosis is more during pregnancy and postpartum due to several reasons like being inactive, hospitalization due to any infection or dehydration, carrying of twins or multiple pregnancy, prolonged labour, birth of child through C-section, and heavy loss of blood after birth of the child.

The blood vessel is blocked and shrinks in case of an injury and leads to the formation of clot in the blood. In an accident, the clot can easily form due to severe damage to the blood vessels. Certain drugs like that of chemotherapy and varicose veins (painful, twisted, and swollen veins) can also harm blood vessels.

The contraceptive pills or birth control pills contains estrogen, the female hormone that allows the clotting of blood more easily, thus increasing the risk of deep vein thrombosis. The pills that are progesterone only pills in which estrogen is not present are free from the risk of DVT. In hormone replacement therapy (HRT), the presence of estrogen is indicated. This therapy is given to women during their menopause.

Many conditions directly affect the circulation of blood and make a person more susceptible to deep vein thrombosis. The medical conditions that increase chances of DVT are heart attack, inflammatory disease, varicose veins, rheumatoid arthritis, cancer and its treatment (chemotherapy and radiotherapy both increase risk of getting DVT), thrombophilia (a genetic disorder), and slow circulation of blood.

Obese people are at higher risk of getting clot in their blood. Obesity is often associated with risk of deep vein thrombosis (DVT). The chances increase even more when you have other symptoms of DVT. The chances of getting DVT are more after a surgery in overweight patient than a normal person. The pressure is increased in veins of the pelvis and legs of an overweight person making him more prone to DVT.

Smoking is another factor that increases the possibility of deep vein thrombosis (DVT). Smokers are always more susceptible to DVT than non-smokers. Smoking affects the circulation of blood making it slow and increases the ability of blood to clot more easily.

The possibility of getting deep vein thrombosis is more in older people than younger ones. Although it can occur at any age but elderly people are more at risk of DVT. The risk increases with increase in age like the chances of DVT are more in people of 60 years or more.