EPP and why light hurts

The rare disease afamelanotide was approved to treat

Erythropoietic protoporphyria, or EPP, makes ordinary daylight cause immediate, severe burning pain. This unit explains the enzyme defect behind it and the light chemistry that turns a sunny day into an emergency.

Understanding EPP is the key to understanding afamelanotide, because the drug does not fix the underlying defect. It shields the skin from the light that triggers the reaction, which is a very different kind of help.