Photo-patch tests make it possible to analyse the phototoxic potential of products or to detect any existing sensitivity caused by UV radiation and at the same time to distinguish this from UVA-provoked reactions, contact allergy or purely irritation-provoked reactions. To achieve this, four test areas are considered for each product, which are treated differently. The product is applied to two areas according to the standard occlusive or open epicutaneous test, the third and fourth test areas remaining untreated. The first reading is taken after the appropriate exposure time. One treated and one untreated test area is then exposed to UV light. Further readings are taken from all areas immediately following the UV exposure and after a further 24, 48 and 72 hours.