Photosensitivity occurs when the skin is overly sensitive to the ultraviolet rays of sunlight and other light sources, such as fluorescent lighting. There are several diseases that cause photosensitivity.
What Causes Photosensitivity?
In porphyria, photosensitivity occurs because porphyrins accumulate and upon exposure to sunlight porphyrins cause damage to the tissue of the skin.
"The photosensitivity of the skin in porphyria is due to porphyrins absorbing ultraviolet radiation in the 400 nm range and emitting an intense red fluorescence. Porphyrins, when irradiated with light of the appropriate wavelength in the presence of oxygen, will cause photodynamic effects. Light energy absorbed by the porphyrin raises electrons into an excited state. Energy released on return of the molecule to its original state reacts with oxygen to produce free radicals and singlet oxygen (O) which damages molecules, cells and tissues.
Unsaturated lipids are particular targets for activated oxygen species; cell damage results from the resulting plasma membrane and lysosomal membrane injury and also from complement activation. Beta-Carotene, also known as β-Carotene, is a known quencher of free radicals and singlet oxygen, has a photoprotective effect in porphyria."
"Porphyrins in their oxidized forms are reddish in color and are also fluorescent. Fluorescent substances, when exposed to light at certain wavelengths, emit light with a different wavelength. Porphyrins appear intensely red when exposed to long-wave ultraviolet light (UV-A). This makes them visible with a Wood's lamp, and enables them to be measured accurately with a spectrofluorometer. Within cells, all porphyrins that are intermediates in the heme biosynthetic pathway, with one exception, are in the reduced form, and are colorless and nonfluorescent. The last intermediate, protoporphyrin, is an oxidized porphyrin. Porphyrins that leave the cells and appear in blood, urine and feces are mostly oxidized and appear reddish to the naked eye and are fluorescent."
It should be noted that erythropoietic porphyria'sare particularly sensitive to the blue light region.
What Are the Symptoms of Photosensitivity?
Photosensitivity occurs on areas of the skin that are normally exposed to the sun such as the arms, hands, legs, and face. Bullae arise from beneath the epidermis of the skin.
Blisters, erosions, redness, swelling, itchiness, pain, comparable to that of a sunburn, and thinning of light-exposed skin
URO I is a highly photo-catalytic molecule. Therefore, exposure of the skin to sunlight results in blistering, vesicle formation, and in some cases leads to severe scarring and deformities, predominantly of the face and hands.