Photosensitivity/Light induced Disorders/Photodermatoses/Photodermatology
Abnormal response of skin to ultraviolet radiation (UVR).
Ultraviolet (UV) radiation:
• non-ionising radiation part of electromagnetic spectrum
• wavelength of 200-280nm (UVC), 280-315nm (UVB), 315-400nm (UVA) (visible light has wave length of 400-700nm and has little biological activity)
• DNA, RNA, urocanic acid, keratin and other proteins absorb the shorter wavelength
• 30% of UVA penetrates to the dermis
• maximum erythema after exposure to the 300-305nm range
• beneficial effects of UVR – production of vitamin D, skin tanning, felling of wellbeing
• therapeutic uses of UVR – psoralen induced photosensitvity (PUVA)
• adverse effects of UVR – sunburn, skin aging (photoaging), carcinogenesis, photodermatoses
• MED (minimal erythema dose) – minimal amount of light of a particular wavelength capable of inducing erythema on the skin (MED of UVB is 1000x more erythemogenic than UVA)
Photosensitivity – the development or exacerbation of a skin eruption and/or symptoms following exposure to sunlight
Photosensitive dermatoses:
Acute – sunburn; phototoxic drug eruptions, lupus erythematosus, solar urticaria
Chronic – polymorphous light eruption, lupus erythematosus, pellagra
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