Dermatologic conditions in horses are notoriously difficult to diagnose and treat; thankfully, veterinary researchers are continually learning more about equine skin.

Diagnosing skin diseases is probably one of the greatest challenges to handlers and veterinarians alike. With such a variety of conditions all looking so similar, it's no wonder common names like "scratches," "greasy heel," and "girth itch" have emerged. These catch-all terms sound like diagnoses, but they actually only describe the clinical signs. Determining which disease is the real cause of that "greasy heel" requires a specially trained eye and, usually, a laboratory analysis.

"Equine skin is particularly sensitive, much like human skin, so there's just no room for experimenting," says Patrick Bourdeau, DVM, PhD, Dipl.EVPC, professor and head of the parasitology, dermatology, mycology, and zoology unit at the Veterinary School of Nantes, in France. "Dermatologic problems require the right treatment from the start, and that generally means a veterinary examination."

The following are descriptions of some of the more common equine dermatologic problems, grouped according to cause.

Allergies and Immune-Mediated Problems

Allergies are a kind of immune-mediated condition, meaning that the horse's immune system overreacts to something (an "agent") in his environment. Skin inflammation, called dermatitis, can cause itching, hives, pain, and open sores–not to mention a great d