Photopatch Testing

In dermatology photopatch tests evaluate the delayed type hypersensitivity that clinically manifests as photodermatoses. This diagnostic test aims to re-create triggering conditions, namely photoallergen + UVA, capable to sustain photodermatoses development. Despite its relatively simple execution, the challenging part remains the result interpretation, in which a mix of experience, clinical training and medical history remain fundamental for establishing the correct diagnosis. In order to minimize the inter-observer variability a validated set of substances were approved by a European Consensus in 2012: 20 substances compose the photopatch test baseline series and additional other 15 substances for special populations. This chapter is centered on photopatch test practical and theoretical aspects in dermatology with a particular focus on methodology.