The process involves the application of various suspected photoallergens on small patches, which are then adhered to the patient's back. Each patch contains a potential allergen that might cause a reaction. After a defined period, usually 24 to 48 hours, one side of the test area is exposed to UV light, typically UVA. The results are observed after another 24 to 48 hours to see if any reactions occur, differentiating between irritant reactions and true allergic responses.
