Allergy is defined as hypersensitivity to one or more allergens, resulting in a marked overreaction of the immune system after repeat exposures. Upon exposure to an allergen, the horse’s immune system produces antibodies called immunoglobulin E. The inflammatory mediators have far-reaching effects and can cause smooth muscle constriction and stimulation of the nervous system.

According to experts, equine allergies, which primarily affect the skin and respiratory tract, are increasingly common. They can be performance-limiting, painful, unsightly, and expensive to diagnose and treat. Secondary problems such as self-trauma can occur that require treatment. Horses can develop allergies at any age and, once affected, remain allergic to those substances for the rest of their lives.