Blood clotting is actually an important function of your body. It's how injuries like cuts and scrapes heal. It prevents excessive bleeding, too.
Blood clotting involves platelets, which are tiny cell fragments in your blood. When an injury happens, platelets stick to the damaged area. They release a chemical that attracts additional platelets to them, plugging the blood flow and allowing the injury to continue with the healing process. Without blood clotting, a small cut could cause you to bleed nonstop.
But blood clotting can be dangerous, too. Sometimes, it can happen too often. Or a clot blocks blood from flowing properly through the body. This is especially dangerous if you're at high risk for or are already recovering from a heart attack or stroke.