Photoallergy. A review

Photoallergic contact dermatitis to 8‐methoxypsoralen in Ficus carica

“…Moreover, in allergic photodermatitis, the inflammatory skin reaction tends to reach a peak earlier (10–24 hr) than in phototoxic dermatitis, in which it usually takes 48–72 hr (39, 41). The difficulty in differentiating toxic from allergic photoreactions can be overcome by performing photopatch tests with serial dilutions of the incriminated substance (39, 42). A higher concentration of the compound or a higher UV energy is needed to elicit toxic than allergic reactions.…”

Self sensitized photooxidation of N-methyl phenothiazine: acidity control of the competition between electron and energy transfer mechanisms

“…where P 0 is the incident photon flux at the wavelength of irradiation (308 nm), α t is the time dependent absorption factor of MPS, F a MPS (t) (= A t MPS /A t tot ) is the fraction of photons absorbed by MPS at time t, A t tot is the total absorbance (sum of absorbances due to MPS and MPSO) and A t MPS is the absorbance of MPS (calculated from the actual concentration of MPS present at time t (eqn (10)).…”

“…The binding of some of these intermediates and products to proteins and the subsequent formation of antigens are thought to trigger the photo-allergic reactions of 2. 10 A study on the in vitro phototoxic potential of stable photoproducts formed by the UV-A photolysis of three phenothiazine derivatives ( perphenazine (3), fluphenazine (4) and thioridazine (5)) in aqueous solution revealed that major photoproducts, such as N-oxides, sulfoxides, and sulfones, exhibit phototoxicities comparable to or even higher than that of the parent drug at the same concentration. 11 Molecular oxygen (O 2 ) is thought to play an important role in the photochemical oxidation reactions of phenothiazine derivatives.…”

What is that thing called light?*

“…This may trigger off a cell-mediated response similar to that seen in allergic contact dermatitis with or without the necessity for further involvement of light (Willis & Khgman, 1968). The term photoallergy tends to be used in this instance (Epstein, 1972), the appearance of reaction being that of eczema (dermatitis) with or without some urticarial or erythematous elements. Some photoactive substances are able to produce both a phototoxic and a photoallergic response.…”