A blood clot is mass of blood that forms when platelets, proteins, and cells in the blood stick together. When you get hurt, your body forms a blood clot to stop the bleeding. After the bleeding stops and healing takes place, your body usually breaks down and removes the blood clot. But sometimes the blood clots form where they shouldn’t, your body makes too many blood clots or abnormal blood clots, or the blood clots don’t break down like they should. These blood clots can be dangerous and may cause other health problems.