Photosensitization in Livestock

Photosensitization in animals refers to a skin condition where the skin becomes abnormally reactive to sunlight. Photosensitivity is an aberrant reaction of the body when exposed to the direct sunlight, owing to the abnormal presence of photodynamic pigments/compounds in the skin cells, cornea or mucus membranes (Mauldin and Peters-Kennedy, 2016). Photosensitization occurs when skin (especially areas exposed to light and lacking substantial protective hair, wool, or pigmentation) becomes more susceptible to ultraviolet (UV) light because of the presence of photodynamic agents. Unlike sunburn and photodermatitis, photosensitization does not result in pathological skin changes in the absence of a photodynamic agent. Upon being energized by the photons of the certain wavelength of sunlight, particularly in ultraviolet range of spectrum; the molecules get energized and when these return to their initial stage, the released energy transfers to the receptor molecules in skin and cause tissue injury either by formation of reactive oxygen intermediates or by changing the permeability of cell membranes. Thus, this reaction is typically a biophysical phenomenon. Photosensitization occurs mostly in cattle, sheep and horses worldwide. (Kumar and Patel, 2013).