Hemophilia is a disease where the blood is too thin and cannot clot properly, causing prolonged bleeding from cuts or injuries. It is inherited through family lines and is more common in males. Symptoms include bleeding that does not stop as it normally would. Diagnosis involves testing by a doctor if bleeding issues are noticed or if there is a family history of hemophilia. It affects around 18,000 people in the United States and is treated by replacing the missing clotting factors through intravenous injections.