Answer
Topical diclofenac can rarely make treated skin unusually sensitive to sunlight, causing a photosensitivity reaction.
Sources for this answer
- Diclofenac diethylamine (Motusol) 1.16% 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.