Answer
Light activates protoporphyrin IX in treated cells, producing a local phototoxic reaction. Burning, pain, redness and swelling are common.
Sources for this answer
- Ameluz 78 mg/g gel — Current selected SmPCemc · Summary of Product Characteristics
- NHSNHS · NHS medicine guidance
General medicine information. Follow the instructions for your own medicine and speak to a pharmacist or clinician about your individual circumstances.