DETERMINATION OF THRESHOLD UV-A ELICITATION DOSE IN PHOTOPATCH TESTING

Photopatch testing, although widely used in the diagnosis of photosens itivity disorders, is not standardized. We performed this study to det ermine the threshold ultraviolet light A (UV-A) dose required to elici t photopatch test responses. 4 patients with previously positive tests were reexposed to the offending allergen, using an incremental dosage regime. Isopropyl dibenzoylmethane (Eusolex 8020), mexenone (benzophe none-10) and oxybenzone (benzophenone-3) produced positive responses a t 1.0, 1.0 and 0.7 J/cm2, respectively. Responses to phenothiazines we re deemed phototoxic. These results demonstrate that high doses of UV- A (e.g., 10-15 J/cm2) are unnecessary, and that 5,J/cm2 should become the current standard.