From the Horses Journal, July 2004

You’ve got to soothe the itch, stop the flies and heal the lesions.

Notice the typical areas of scaling intermixed with oozing and hair loss. The inflammation was severe enough to cause prominence of the veins along the belly.

Midline dermatitis is the technical term for that "line" of bites you sometimes see underneath your horse’s belly. It’s also called "sweet itch."

Whatever the name, this angry inflammatory reaction includes hair loss, swelling, redness and often open, oozing areas. Primarily a fly-season problem, midline dermatitis is caused by an allergic reaction to biting flies or midges, usually Culicoides.

It may also be complicated by the insect bites introducing larvae of the parasite Onchocerca into the wound, with further allergic and/or inflammatory reactions to the larvae.

Fortunately, the Onchocerca is sensitive to ivermectin, so deworming with this drug will eliminate that part of the problem. An ivermectin treatment is standard for midline-dermatitis problems.

An allergy to Culicoides bites, however, is more difficult to control, and many horses battle this problem every year with little relief. The mare in the belly photo resides in California and had problems year round. She was also intensely itchy—and grumpy.

She’d battled midline dermatitis for seven years, had intensive treatment with monthly ivermectin and a variety of topical medications, including steroids, aloe, insecticides, antifungal creams and sprays, Bactine and other skin creams with either no effect or even worsening of the problem.

The human product Gold Bond powder, which the owners were able to "puff" on from a distance without actually touching her sore spots, provided temporary relief. However, the lesions would not heal.

Since a key element in eliminating allergic reactions is to avoid exposure to the allergen, preventing the Culicoides bites seemed a smart place to start. These midges are notoriously difficult to repel and aren’t fazed by standard fly-spray ingredients. As a better remedy, we mixed 1/4 teaspoon of the human product Campho-Phenique (available in drug stores) and 1/4 teaspoon of Calm Coat into a 13 oz. jar of petroleum jelly (Vaseline or a generic). The petroleum jelly provides a barrier, while the Campho-Phenique is a barrier, repellent, anesthetic/disinfectant. Calm Coat is thick, providing a barrier, soothing essential oils and repellent action.

The result is thick mixture that holds against the skin. With a small spatula, scoop the mixture out and apply it in a thick layer two to three times a day or anytime the horse seems itchy. The itch relief should be immediate (the Campho-Phenique is also anesthetic). For our trial mare, the lesions scabbed over and healed within a few weeks.