This disease causes the skin to be sensitive to sunlight. A person with this disorder must always stay out of the sun, or they will get a sunburn. People with this disease are often called a "Moon child" because they can only go outside during the night. This disease is present in both genders and in all races, with one in 250,000 people living in the US having this disease. A Japanese person is about six times more likely to have this disease.