Photoallergic contact dermatitis due to diphenhydramine hydrochloride

Photoallergic contact dermatitis

“…For most of the photoallergens, the action spectrum lies in the UVA range, but some elicit reactions in both the UVA and UVB range as is the case with diphenhydramine hydrochloride (3, 4) and non‐steroidal anti‐inflammatory agents (NSAIDs) (5).…”

Concomitant allergic contact dermatitis from diphenhydramine and metronidazole

“…Diphenhydramine hydrochloride is an H 1 receptor antagonist, which rarely can trigger allergic and/or photoallergic contact dermatitis (5–9). Photoallergic contact dermatitis caused by diphenhydramine hydrochloride is rare, and only 4 cases have been reported in the English medical literature (5–7), and only 1 case of the coexistence of both allergic and photoallergic contact dermatitis caused by diphenhydramine has been previously described (6). In our case, the reactions to the patch test and the photopatch test were equally positive; so, photoallergy or photoagravation from diphenhydramine were not considered likely.…”

“…Metronidazole is an imidazole derivative used against parasites and anaerobic bacteria which seldom causes allergic contact dermatitis (1–4). Diphenhydramine hydrochloride is an H 1 receptor antagonist, which rarely can trigger allergic and/or photoallergic contact dermatitis (5–9). Photoallergic contact dermatitis caused by diphenhydramine hydrochloride is rare, and only 4 cases have been reported in the English medical literature (5–7), and only 1 case of the coexistence of both allergic and photoallergic contact dermatitis caused by diphenhydramine has been previously described (6).…”

Photoallergy

“…Although delayed pigmentation is caused by UVB, immediate pigment darkening is more due to UVA (40,41). Action spectrum for majority of photoallergens is within UVA range; although UVB has also been associated with some photoallergens, it has minimal clinical relevance in case of PACD (42)(43)(44).…”