During hemostasis, the normal stagnation of bleeding, a blood clot forms through the process of coagulation, but sometimes a clot forms inside a deep vein. Known as deep vein thrombosis (DVT), this kind of blood clot poses serious health threats.

According to the American Thrombosis Association, approximately 2 million people are affected by DVT each year and around 74 percent of Americans are unaware of the disease.

Types
Relatively harmless clots known as superficial phlebitis can form near the surface of the skin in small veins.

On the other hand, DVT, which typically afflicts a leg, can break loose and travel through the blood steam to the lungs, resulting in a fatal pulmonary embolism (PE).

If a clot travels to the heart it will cause a heart attack; if it's to the brain, it will cause a stroke.

Causes
A blood clot can occur in many places throughout the body. Most form when something prevents blood from circulating normally.