What are Blood Clots?

Blood clots may form inside small veins near the surface of your skin (superficial phlebitis), resulting in localized redness, pain and swelling. Superficial phlebitis rarely causes complications and requires minimal treatment. Blood clots that form inside larger, deeper veins (deep vein thrombosis) may cause more-widespread symptoms in the affected area, usually your leg, and can cause more-serious problems.

Blood clots may also break away from their original source and cause damage elsewhere in your body. Blood clots that break away from a deep vein thrombosis and travel to your lungs may cause a potentially life-threatening blood clot in the lungs (pulmonary embolism).

Blood clots that arise in one of the chambers of your heart, usually due to an irregular heart rhythm such as atrial fibrillation, may travel to your brain and cause a stroke. Blood clots that arise in the arteries of the heart itself may block the flow of blood through that artery and cause a heart attack.

Blood clots that arise from within the carotid arteries in your neck may travel to the brain and cause a stroke.

Factors and conditions that can cause blood clots, as well as serious conditions that are associated with blood clots once they form and travel to other parts of your body, include:

•Antiphospholipid syndrome
•Arteriosclerosis / atherosclerosis
•Certain medications, such as oral contraceptives, hormone therapy drugs and some breast cancer medications
•Deep vein thrombosis
•Factor V Leiden
•Family history of blood clots
•Heart arrhythmias
•Heart attack
•Heart failure
•Obesity
•Peripheral artery disease
•Polycythemia vera
•Pregnancy
•Prolonged sitting or bed rest
•Pulmonary embolism
•Smoking
•Stroke
•Surgery