Hemophilia is a condition in which blood does not clot well — it does not thicken and seal a cut the way most people’s blood does. A person with hemophilia can bleed for a long time from a small wound, and can also bleed inside joints and muscles, which is painful and damaging. It often runs in families, and it is much more common in boys and men, though girls can have it too. This is the American spelling; British English writes haemophilia. Though actually, the ending -philia usually means a love of something, so the word looks as if it meant love of blood. It does not. Here the scientific naming only means the blood has a strong tendency toward bleeding. Older English sometimes called it the royal disease, because it appeared in some European royal families, but the medical name is hemophilia.