Horse Photosensitisation Welfare and Management

Equine photosensitisation causes severe sunburn-like skin reactions in unpigmented areas, typically secondary to liver disease or ingestion of photosensitising plants.

Key Facts

Primary photosensitisation occurs after ingestion of plants containing photodynamic agents including St. John's Wort
Hepatogenous photosensitisation results from liver damage causing phylloerythrin accumulation in the skin
Lesions appear as oedema, vesicles, crusting, and sloughing of unpigmented skin on the nose, white markings, and coronary band
Diagnosis requires investigation of liver function, plant exposure history, and skin biopsy
Severe cases require systemic anti-inflammatory treatment, wound management, and removal from the sensitising source

Welfare Considerations

Photosensitisation causes acute and severe pain from sunburnt, blistered, and sloughing skin that can affect extensive areas of the face, legs, and back. Horses with severe photosensitisation show obvious distress, head-shaking, and reluctance to go outside. The condition requires urgent veterinary investigation as hepatogenous photosensitisation indicates underlying liver disease that needs treatment in its own right. Protection from sunlight through stabling during daylight hours, UV-protective fly rugs, and topical wound management reduce welfare harm during recovery.

What You Can Do

Stable horses with unpigmented skin areas during peak sunlight hours in summer
Investigate unexplained skin reactions on unpigmented areas promptly with veterinary advice
Remove horses from pastures where photosensitising plants including St. John's Wort are present
Apply high-factor sunscreen to vulnerable unpigmented areas of horses spending time outdoors