Raised weals or rings on the skin surface with prominent change in the direction of the hair coat, they are itchy and occasionally serum may ooze through the skin surface. Hives are usually seen on the skin of the neck, hindquarters and belly but can be anywhere. The cause is a localised allergic reaction to insect bites, stings, infections, parasites, feed allergens or occasionally medications. They are a symptom of an underlying hypersensitivity reaction, but the stimulating cause may be very difficult to pin down. Generally, they appear suddenly and dissipate in a day or two without treatment, though recurrence can be a problem in some horses requiring investigation of the cause and veterinary treatment. The cause is often never established but fortunately most instances are self-limiting.