Photosensitivity in animals

In other cases, the photodynamic substances may be produced in the body itself due to inborn errors in pigment metabolism, especially those involving the heme synthesis.

In some cases (Type I), pigments are excreted through urine or deposited in hard tissues such as bones and teeth, causing discolouration.

Affected animals should be protected from direct sunlight until the photodynamic compounds have been completely eliminated from the body or the appropriate treatments have been given.

Type I Photosensitivity occurs when the photodynamic compounds need not undergo metabolism to be activated and so may accumulate under the skin directly following ingestion.

A common condition seen in animals is congenital porphyria due to the accumulation of Uroporphyrin, which is deposited in the teeth and bones, giving them a pink discolouration, or excreted through the urine, exhibiting a pinkish fluorescence under ultraviolet light.

In Type III Photosensitivity, damage to the biliary transport mechanism prevents the excretion of phylloerythrin, allowing the photodynamic substance to enter the circulatory system and accumulate under the skin.