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United States Department of Agriculture

Agricultural Research Service

Title: Equine Photosensitization

Author
item Stegelmeier, Bryan

Submitted to: Clinical Techniques in Equine Practice
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 1, 2002
Publication Date: June 1, 2002
Citation: Stegelmeier, B.L. 2002. Equine photosensitization. Clinical Techniques in Equine Practice.

Interpretive Summary: Photosensitization is light-induced dermatitis caused by heightened sensitivity of the skin to sunlight. Generally heightened sensitivity and reactivity is due to the presence of photodynamic agents or chromophores in the circulation and skin. The clinical signs of photosensitizational dermatitis generally develop within hours after exposure to strong sunlight. Hair and dermal pigments are protective as they absorb light energy before it activates chromophores and damages dermal tissues. Thus, lightly pigmented areas with little hair protection especially the muzzle, ears, eyelids, face, tail, vulva, and coronary bands that are exposed to the sun are most severely affected. Clinical signs include photophobia and discomfort seen as scratching and rubbing the ears, eyelids and muzzle. Affected areas develop erythema followed by edema, serous exudation, scab formation and skin necrosis. Equine photosensitivity is generally caused by plant or fungal products, drugs, chlorophyll metabolites or other chemicals. Common causes of photosensitization, including primary photosensitization and secondary or hepatogenous photosensitization are reviewed.

Technical Abstract: Photosensitization is light-induced dermatitis caused by heightened sensitivity of the skin to sunlight. Generally heightened sensitivity and reactivity is due to the presence of photodynamic agents or chromophores in the circulation and skin. The clinical signs of photosensitizational dermatitis generally develop within hours after exposure to strong sunlight. Hair and dermal pigments are protective as they absorb light energy before it activates chromophores and damages dermal tissues. Thus, lightly pigmented areas with little hair protection especially the muzzle, ears, eyelids, face, tail, vulva, and coronary bands that are exposed to the sun are most severely affected. Clinical signs include photophobia and discomfort seen as scratching and rubbing the ears, eyelids and muzzle. Affected areas develop erythema followed by edema, serous exudation, scab formation and skin necrosis. Equine photosensitivity is generally caused by plant or fungal products, drugs, chlorophyll metabolites or other chemicals. Common causes of photosensitization, including primary photosensitization and secondary or hepatogenous photosensitization are reviewed.

Last Modified: 10/22/2014
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