Immobility or Inactivity
Long periods of standing or sitting increase your risk because the lack of muscle contractions inhibits proper blood flow. The lack of blood flow increases the risk of blood clots forming.
Foods that are poor for heart health can also increase the risk of blood clots. For example, a diet high in excess salt, refined sugars, and unhealthy trans fats can cause inflammation and affect blood flow.
Cancer and cancer treatments, physical trauma to a vein, certain surgeries (especially of the abdomen, hip, knee, or pelvis), heart and lung diseases, liver and kidney diseases, diabetes, high blood pressure, high cholesterol, and family history increase your risk.
Smoking tobacco affects the platelets in the blood, making it easier for them to stick together and clump. Furthermore, smoking damages blood vessel walls, affecting blood flow and increasing the risk of clots.