Standard photopatch test battery? Proposal based on current epidemiology and experience in our Skin Allergy Unit

Abstract

Photoallergic contact dermatitis (PACD) occurs after topical application of a photosensitizing substance. It is a type IV hypersensitivity reaction in which a chromophore absorbs radiation, mainly from the ultraviolet A (UVA) spectrum, and is transformed into a photoallergen in the skin. Parallel to non-photoinduced allergic contact dermatitis, patients must be previously (photo) sensitized. Due to the necessary involvement of sunlight in provoking the skin lesions, they do not typically appear in areas that are anatomically protected from the sun, for example, upper eyelids and retroauricular folds.Involvement of the rest of the face and neck should raise suspicion on PACD. 1 Diagnosis is confirmed by photopatch testing (PPT), which consists of applying allergens to be studied in duplicate and exposing only half of them to broad-spectrum UVA radiation (320-400 nm) at a dose of 5 J/cm 2 after the first 24-48 hours [day (D)1 or D2] of occlusion (eg, coinciding with the first reading). Final reading usually takes place on D4 (96 hours). 2 In Spain, the latest recommendation of an standard PPT battery (1995) included 16 allergens. 3 According to European guidelines, proposals of modifications have been made at a national level.Nevertheless, we still lack a more recent, formal, and standardized PPT recommendation. Therefore, the decision on which allergens to test is often guided by clinicians suspicion and the dermatologist's experience in this field. 3

Innovative Strategies for Photoallergy Assessment: Breaking Free from Animal Models in Cosmetic Ingredient Development

“…Identifying photoallergy presents challenges due to complex clinical presentations, broad differentials, and a scarcity of specialists conducting photo-testing [103]. Therefore, standardizing the panel agents as well as the patch-test procedure is crucial not only to facilitate comparisons among studies, but also to swiftly incorporate new agents when necessary [107,108]. Moreover, is important that physicians can recognize and manage drug-induced photosensitivity early by reviewing constantly renewed information [109].…”