Skin is the largest organ of a horse’s body and one of the most vulnerable as it protects against an array of external threats such as bacteria, environmental allergens, chemicals and extreme temperatures. Good grooming and management practices can help to keep skin healthy. But problems still may arise. Here’s a look at a variety of common equine skin conditions (arranged alphabetically) along with suggestions for care. Your veterinarian will also be a valuable resource in confirming the identity of any skin ailment and recommending treatment.

• Aural plaques: flaky white patches on the inner surface of the ear; occur when chronic fly irritation causes inflammation. Topical application of an antiviral or steroid cream can clear the plaques and soothe skin, but any pigment loss under the skin is permanent. Ear hair provides a natural defense against flies, so minimize trimming as a preventive. Protect clipped areas with repellent or a fly mask with ear covers.

• Dandruff: skin oil that sheds from the coat as either small, dry flakes or large, waxy crusts. Dry dandruff typically forms at the base of the mane and tail and on the girth area; oily dandruff usually appears on the elbows, hocks and lower legs. Either type results from a variety of causes, including allergies, insects, poor nutrition and undiagnosed illness, but the most common causes for crusty, scaly skin are bacterial infections (Staphylococcus). Some breeds, such as Thoroughbreds and Arabians, are more affected than others. Anti-dandruff shampoo formulated for horses can dissolve flakes and scales; products containing an antibacterial such as chlorhexidine will help to resolve large, waxy crusts; and a feed supplement may improve skin and coat condition.

• Hives: soft, raised, itchy bumps that develop and disappear often suddenly as part of a reaction to an insect bite or sting, medication or exposure to an allergen. May be seen on any part of the body, but mainly occur on the back, flanks, legs, neck and eyelids. Hives usually resolve without treatment; identifying and preventing exposure to the causative agent may be necessary in chronic cases.

• Insect bite hypersensitivity: allergic skin disease caused primarily by the saliva of insects of the genus Culicoides (midges, gnats, no-see-ums). Signs include itching, skin thickening, lesions, scaling, crusting, hair loss and hives. Appears primarily on the face, mane, ears, trunk and tail. Corticosteroids can relieve the cycle of itching, but prevention is key: Apply fly spray; stable horses at dusk and dawn (the insects’ preferred feeding times); use fans to create air currents too challenging for the flies to navigate; and maintain a clean, dry environment to disrupt breeding and reduce numbers.

• Lice: tiny wingless parasitic insects that live in the haircoat and are visible upon inspection. There are two types: chewing, which feed on hair and dead skin, and blood-sucking. Both cause itchiness, and horses may bite at or rub infested areas, causing hair loss and skin damage. Sucking lice create small wounds that may become infected. To treat: Use a spray containing pyrethrin, synthetic pyrethrin or the organophosphate coumaphos.

• Mange: infestation by a parasitic mite that feeds by piercing the skin or burrowing into it. Signs include red, moist, crusty skin patches and intense itching over the body (sarcoptic mange), ears (psoroptic mange) and lower legs (chorioptic mange). The condition is passed from horse to horse through direct contact or via shared equipment. A topical or oral acaracide, such as ivermectin or moxidectin, will eliminate mites. A topical shampoo may help to remove crusting and scabs.

• Melanoma: tumor of the skin cells that produce pigment (melanocytes); common in aging gray horses due to the gray gene; appears as a raised, round, firm black nodule; typically found under the tail, around the anus, on the eyelids and in the corners of the mouth. Most melanomas are benign, and horses may require no medical intervention. Treatment options include removal via surgery, cryotherapy or laser; local chemotherapy; oral medication and immunotherapy.

• Photosensitivity: painful inflammation of lightly or unpigmented patches of skin; much more extensive than sunburn. Results from the ingestion of certain plant toxins that eventually circulate in the capillaries near the skin surface and are activated by sunlight. The toxins are present in a number of common pasture plants, including St. John’s wort, buckwheat, bishop’s weed, spring parsley and some varieties of clover, particularly alsike. Photosensitivity may also be related to a few types of antibiotics (tetracyclines) and impaired liver function. To treat: Relieve pain, prevent infection, eliminate exposure to the cause, apply sunblock and outfit horses in UV protective sheets and masks.

• Rainrot: crusted, painful skin infection caused by Dermatophilus congolensis, a microorganism that resembles bacteria and fungi and normally lives on skin. Wet conditions stimulate the release of spores and spread the infection. Treatment involves antibiotics. Topical antibacterial shampoo may be used to soak scabs so they can be removed. Clipping affected areas may be necessary. Isolate infected horses to reduce the spread of disease. 

• Ringworm: fungal infection that appears as an itchy, circular pattern of hair loss, usually on the girth and saddle areas. The fungi are found in soil and can be picked up when a horse digs, rolls or lies down. Typically, the infection is transmitted through shared tack and grooming supplies. Ringworm can clear without treatment. Antifungal shampoo or topical therapy can speed recovery. To prevent spread and recurrence, disinfect equipment and other potentially contaminated surfaces.

• Sarcoid: tumor caused by papillomavirus infection; usually not painful or itchy. There are six distinct types:

• verrucose–gray, flat, scaly with an irregular surface, slow-growing; often seen on the face, trunk or sheath; the least aggressive sarcoid tumor
• occult–small, flat, gray, hairless, slow-growing; may not change for years; usually occurs around the mouth and eyes, on the neck and relatively hairless areas, such as the inside of the forelimbs, armpits and thighs
• nodular–distinct solid lump; may ulcerate and bleed, can appear singly or number in the hundreds usually on the groin, sheath or eyelids
• fibroblastic–aggressive and fast-growing, irregularly shaped, firm, fleshy raised lump; usually smooth and hairless; may ulcerate and bleed; often occurs in clusters on the eyelid, groin, lower limbs, coronary band and the site of a skin wound or trauma
• mixed–a combination of two or more types
• malevolent–rare, aggressive tumor that spreads extensively through skin; may ulcerate and bleed; often forms on the jaw, face, elbow or inner thigh.

Treatment options for all types of sarcoids include surgical removal, immunotherapy, chemotherapy, cryotherapy and laser surgery. The recurrence rate in horses is high.

• Scratches: painful scabby or oozing skin infection above the heels; caused by a mix of bacteria, fungi and parasites that enter breaks in skin; most often occurs when footing is excessively wet, muddy or dirty. Mild cases may resolve by cleaning and clipping the affected area and keeping it dry. Severe cases may require topical treatment with an antibacterial, antifungal or steroid alone or in a mix; oral antibiotics may be necessary for extensive conditions.

• Summer sore: itchy, inflamed lesion caused by the migrating larvae of gastric worms (Habronema and Draschia species); may become swollen and raw as horse rubs, ooze blood-tinged fluid and fill with lumpy, reddish granulation tissue. Treatment includes topical or systemic glucocorticoids or a topical mixture of glucocorticoids and dimethyl sulfoxide (DMSO); excess granulation tissue may require surgical removal. 

• Sunburn: painful reddening, inflammation and possible blistering and peeling of pale or nonpigmented areas of the skin caused by overexposure to the sun’s ultraviolet rays. Treat with a soothing, moisturizing topical ointment, such as zinc oxide or silver sulfadiazine. To prevent: Stable during the day, provide shade outdoors, apply UV sunscreen (a horse-specific product or one that is child-safe, at least SPF 30), use protective fly sheets and masks.

• Sweet itch: allergic skin disease caused by biting midges (Culicoides). Salivary proteins injected into the skin cause intense itching. The mane, tail and withers are most often affected. Rubbing to relieve the itch can produce open wounds and secondary infections. Treatment may rely on topical corticosteroids and/or antihistamines. Preventive measures include insect repellent, fly sheets, face and ear masks and stabling from dusk to dawn when Culicoides are most active.

• Vitiligo: autoimmune destruction of cells that produce melanin, the natural pigment that colors skin and hair. Appears as white or light patches that vary in size and location; often develops around the lips and on the muzzle and eyelids. Vitiligo is more common in gray horses; it is linked to an immune response against melanomas, which may be present in the perineal and tail areas. There is no treatment.

• Warts: small, rough, gray-white growths caused by papillomavirus; often seen on the muzzle, ears, genitals and pasterns of horses age 4 and younger whose immune system has yet to fully mature. Most warts resolve on their own. Treat inflamed or sore spots with an over-the-counter antiseptic or topical moisturizing lotion. Surgery, topical cream or cryosurgery may be an option for warts causing discomfort. Papillomavirus is contagious, so quarantine any infected individual, don’t share equipment and disinfect all surfaces to kill lingering organisms.  

Practical Horseman thanks Rosanna Marsella, DVM, DACVD, for her technical assistance in the preparation of this article. A veterinary dermatologist, Dr. Marsella is a professor at the University of Florida College of Veterinary Medicine in Gainesville, where she also serves as the director of the laboratory of comparative dermatology.