Adequate controls are imperative to differentiate phototoxicity from photoallergy. In phototoxicity, all controls will have a positive response, whereas in photoallergy, controls should be negative. The histopathological findings in berloque dermatitis are identical to other phototoxic reactions, an irritant cutaneous response. The epidermal changes consist of keratinocyte necrosis, intercellular and intracellular edema, and intraepidermal blisters. In severe cases, these blisters may rupture, resulting in subepidermal bullae.
Neutrophils enter the epidermis at an early stage.
In contrast to the extensive epidermal damage, only a mild perivascular infiltrate is present. Changes associated with berloque pigmentation are an increased number and size of melanosomes, melanocyte hypertrophy with increased arborization of dendrites, increased transfer of melanosomes to keratinocytes, and increased tyrosinase activity within the proliferating melanocytes. The primary aim of the therapeutic regime is discontinuation of the offending substance. If berloque dermatitis is the putative diagnosis, all bergamot oil-containing perfumes should be avoided. Any perfumes that are worn should be worn on covered-up areas, not on areas of sun exposure.