Veterinary Handbook Disease Finder



Other Names

  • Facial Eczema



Photosensitisation is the clinical condition in which skin is damaged by photodynamic agents of dietary origin that react to sunlight. 

Phylloerythrin is the most important of the light-sensitive pigments causing skin disease in grazing ruminants in Australia, but there are other agents that may also cause the same disease. Phylloerythrin is produced by fermentation of chlorophyll (that is present in all green plants) in the rumen. Phylloerythrin is absorbed and carried in blood and normally excreted in bile by the liver. Sunlight penetrating unprotected skin can cause fluorescence of pigment within superficial blood vessels and result in damage to tissues of the skin including the small blood vessels. 

Phylloerythrin may be retained in the circulation by simple overload of the excretory capacity of the liver when young sheep and goats are exposed to succulent, immature forage such as early growth lucerne, perennial rye grass, clover or canola (rape). Outbreaks also occur secondary to liver damage from some other cause that impedes the excretion of even normal levels of the pigment. 

Acute clinical cases of photosensitisation at assembly points would be unusual and dependant on exposure of animals in the period prior to assembly, but significant residual lesions on the skin can affect large numbers of animals. The highest risk is generally in late winter and spring when pastures are rapidly growing and there may be less cloud cover.

Clinical Signs and Diagnosis

Affected areas of skin become itchy, blisters develop, and scabs form. Non-pigmented skin areas and those with minimal wool covering are most likely to be affected, such as face, ears, and feet. Affected skin may become necrotic and ulcerate, and covering fleece may be ragged and lost along the back. Animals with short wool, especially with open fleeces, may be affected along the dorsal midline. Face and ears are swollen, ears droop, tears are excessive, and a bright band of redness is present on the coronet. Head shaking and shifting lameness may occur if the skin of the face and legs is involved. 

Affected cattle may show skin damage along the back and on the sides of the udder, depending on where non-pigmented skin is located. 

Clinical signs are usually adequate for diagnosis but must be differentiated from sunburn. Jaundice, if present, indicates liver disease.


Protect from direct sunlight. Deny access to green feed. Secondary skin infections may require antibiotics. Prevent flystrike.


Screen out animals with skin lesions during selection. Avoid grazing animals on hepatotoxic and phototoxic plants that may have emerged in holding paddocks at assembly points.