Photograph of a baby suffering from haemophilia, showing a large area of bruising (haemorrhaging) over the infant's left chest. Haemophilia is a hereditary disorder in which the blood clots very slowly, due to a deficiency in one of the blood coagulation factors (antihaemophilic factor or Factor VIII). Haemophiliacs may endure prolonged bleeding following an injury or wound, and in severe cases spontaneous bleeding into muscles and joints. Bleeding may be treated by giving infusions of blood plasma or concentrated Factor VII. Recently, haemophiliacs have been exposed to the AIDS virus through contaminated Factor VIII.