POP QUIZ

c. something he touched. The welts are most likely hives, which are soft, raised, rounded wheals on the skin caused by an allergic reaction. Hives “pit” under the pressure of your thumb and generally are not painful, although they may be itchy. The most common cause of hives in horses is a contact allergy—an immune overreaction to something that touched his skin, such as an ingredient in a new grooming product. Insect bites may also be the culprit but they are more likely to result in inflamed, itchy patches of skin. On the other hand, hives caused by food allergies are rare in horses. If the swelling is nowhere near a horse’s head or muzzle, hives require no treatment and will go away on their own. (But you’ll need to figure out what triggered them so you can avoid causing additional, possibly more serious, allergic reactions in the future.) However, hives that affect a horse’s vision or impinge on his airways may need to be addressed by a veterinarian, who will most likely administer corticosteroids to control the swelling.