Therapeutics in Dermatology
A reference textbook in dermatology
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11 June 2012, by JEANMOUGIN M.

Photosensitization is caused by an interaction between light (most commonly solar) rays with a given wavelength and a photosensitizing substance (chromophore) which is activated after absorbing the light ray. Photosensitivity reactions are most common in the skin because it is naturally exposed to the sun’s rays. A photosensitizing substance or photosensitizer may be produced by a metabolic disorder (porphyria or pellagroid syndromes) causing endogenous photosensitization, or by a substance introduced into the body either systemically or through direct contact: this is exogenous photosensitization. Systemic photosensitization is mainly caused by medicines administered either orally or intravenously, or rarely foods. Contact photosensitization is caused by topical medicines, cosmetics and plants.

There are three stages in treatment. First of all, the healthcare provider must clearly establish that the photosensitivity reaction is of the exogenous type. Secondly, the photosensitizing substance must be identified and then eliminated.

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