The blistering and peeling most often occurs in horses that have a high percentage of white hair and pink skin and is a result of sunburn. Most commonly, pinto and paint horses are affected. However, horses with a large amount of white on the face may have reactions. Pigmented hairless areas are most severely affected, especially around the muzzle. Most often what is occurring is a photosensitization. This is an allergic reaction to sunlight. Certain plants, usually legumes such as the clovers and possibly fescue grass, develop chemicals in their leaves that get into the bloodstream. These chemicals cause the skin to have an allergic reaction when hit by light. The skin looks as if it has been severely burned. It blisters, weeps, cracks and may even slough off. The horse should be kept inside during the day or allowed access to shaded areas. Although the appearance of the horse may be ghastly, nearly all horses completely recover.