The reaction to a photoallergen
is based on the same immunological mechanism as contact allergy.
Photo patch testing is helpful only if a photoirritant is converted to a photoallergen
and the process becomes immune mediated.
In the diagnosis of photoallergic contact dermatitis, photopatch testing is a crucial/important tool, performed by applying suspected photoallergens
to the back in two sets, and subsequent reaction reading (4,34,35).
1c); epicutaneous testing using the Portuguese Contact Dermatitis Group (PCDG) Standard Series, plants and woods were negative; non-irradiated epicutaneous tests (stand-ard photoallergens
) were negative; and irradiated photoepicu-taneous tests (standard photoallergens
- 5 J/c[m.sup.2]) were globally positive (Table 1).