Erythropoietic protoporphyria is an uncommon type of porphyria that mainly affects the skin. The disorder results from reduced levels of the enzyme responsible for the eighth and final step in heme production. Heme is a vital molecule for all of the body's organs. It is a component of hemoglobin, the molecule that carries oxygen in the blood. Erythropoietic protoporphyria is a subtype of porphyria. This type of porphyria causes the skin to be overly sensitive to sunlight. Beginning in childhood, areas of skin exposed to the sun (particularly the face and hands) develop itching, stinging, and burning that lasts for hours to days after exposure. The skin becomes red and swollen in some cases, but usually heals without scarring. These signs and symptoms are often milder than the skin damage seen in other types of porphyria. No factors other than sun exposure are known to trigger symptoms. Some people with erythropoietic protoporphyria have gallstones beginning at an early age. A minority of people with this condition develop liver damage that can be severe or life-threatening.