ABSTRACT
Photo-allergic contact dermatitis is an uncommon reaction, thought to be caused by cell-mediated hypersensitivity. A photo-activated chemical is considered to behave as an antigen or hapten, eliciting an immunologic response, which requires ultraviolet irradiation for both the induction and elicitation phases. Photo-allergy is not to be confused with phototoxicity (see Chapter 12), which may theoretically occur in any individual exposed to sufficient phototoxic chemical and light of the appropriate wavelength, and which is considered to be a non-immunologic event (125).
