Normal blood coagulation is a complex process involving as many as 20 different plasma proteins, which are known as blood clotting or coagulation factors. Normally, these factors interact with other chemicals to form a substance called fibrin that stops bleeding. When certain coagulation factors are deficient or missing, the process is impaired. Bleeding problems can range from mild to severe.

Some bleeding disorders are present at birth and are caused by rare inherited disorders. Others are developed during certain illnesses (such as vitamin K deficiency or severe liver disease), or treatments (such as use of anticoagulant drugs or prolonged use of antibiotics).

Bleeding disorders can also result from a decreased number of (or impaired function of) platelets, the blood cells that promote blood clotting. These disorders can also be either inherited or acquired. The acquired forms often arise from the side effects of certain drugs.