Photo-sensitivity is a severe skin dermatitis that occurs in the non-pigmented (white skinned) areas of horses when exposed to sunlight, following ingestion or contact with certain plants or secondary products that are UV or light reactive.
Primary or acute exposure is caused by ingestion of a photodynamic substance, such as certain plants and a number of different drugs and medications.
Primary Photo-sensitivity Causing Plants
- Queen Anne’s Lace
- St. John’s Wart
- Giant Hogweed
Secondary Photo-sensitivity is the most common type of photo-sensitivity seen in animals and occurs due to liver or bile duct damage, most often as a result of ingestion of poisonous weeds and mycotoxins over an extended period of time.
Secondary Photo-sensitivity Causing Plants
- Tansy Ragwort
- Pattern’s Curse
- Hound’s Tongue
Symptoms can appear on the ears, muzzle, white skinned areas, and the coronary band. Symptoms include:
- Skin Necrosis
- Skin Thickening