- n.any of various skin diseases caused by exposure to light of varying wavelength (see photosensitivity). The facial prominences and the ‘V’ of the neck are most commonly affected, the shadow areas behind the ears and below the chin being protected. A common photodermatosis is polymorphic light eruption, which affects 10% of the population. It appears with the first sunshine of spring and abates by late summer. The photodermatoses include certain porphyrias, notably porphyria cutanea tarda.
The new mediacal dictionary. 2014.