As a modern term, "sweet" denotes pleasure and enjoyment. But for a horse, sweet itch is anything but sweet.

"Sweet itch, also known as summer eczema or equine dermatitis, is one of several seasonal allergies that your horse may encounter," notes Glennon Mays, DVM, clinical associate professor at the Texas A&M College of Veterinary Medicine & Biomedical Sciences.

"Equine dermatitis can have varying causes," explains Mays. "Allergens may irritate your horse’s skin, but viruses and bacteria might also manifest themselves as dermatitis. These foreign agents can cause inflammatory conditions in the skin and may affect your horse’s hair coat. Equine sweet itch is a seasonal allergic skin condition that can be caused by fly bites or midge bites. Horses that suffer from sweet itch have developed an allergy to these bites."

Insects flourish in the summer, and horses can have sensitivities to insect bites, notes Mays. In particular, black flies (also known as buffalo gnats) are known to seek out horses as hosts. These flies feed on mammals’ blood and are attracted to hosts by smell, heat, and sight. They prefer to feed on the host’s head, hair, and ears but will also bite any exposed skin.

"The female black flies are blood feeders," explains Mays. "The fly bites by cutting into the skin and feeding on the pooled blood. Anticoagulants injected (by the fly) into the feeding site cause an allergic reaction, and antigens in their saliva can cause allergic reactions as well."

Mays notes, "Additionally, the black fly bite can become painful and itch