The difference between photoallergy and phototoxicity.
| Photoallergy | Phototoxicity | |
|---|---|---|
| Dosage of drug required | Small | Large |
| Onset | >24 hours | Minutes – hours |
| Clinical features | Dermatitis (acute, subacute or chronic) on exposed skin but may also spread to unexposed areas | Exaggerated sunburn only on exposed skin |
| Persistent light reaction | Yes | No |
| Histopathology | Epidermal spongiosis | Degeneration of epidermal cells |
| Dermal mononuclear cell infiltrate | Dermal vasodilation and oedema | |
| Exocytosis of mononuclear cells | Sparse mononuclear infiltrate | |
| Adapted from Gould JW et al. 4 | ||