There are many problems that can affect the skin caused by everything from insect bites and allergies to fungal, viral or bacterial infections.

Hillary Jackson, a veterinary dermatologist at North Carolina State University, sees many types of skin problems in horses. Some of the most common are bacterial and fungal infections.

Fungal Infections

“Typically, a fungal infection like ringworm is characterized by patchy areas of hair loss,” said Jackson. “It may not always be in a circular pattern, which is what most people expect to see. Ringworm is contagious between horses–and zoonotic, which means people can get it too.”

So, when handling or treating the horse, you need to take precautions to not get ringworm yourself.

“Generally, horses acquire [ringworm] from another affected horse, or from spores that can live in the environment a long time,” she explained. “Once you have an infected environment, the spores can persist for years. Horses on your place may continue to develop ringworm, especially if you bring new horses in, or have young or sick animals, since they may have less resistance. The spores can also be carried on tack or grooming tools and spread from horse to horse.”

A definitive diagnosis of ringworm requires a culture–plucking hairs from around the hairless area for testing–because other skin problems can mimic ringworm. “And, often, when they don’t think it’s ringworm, that’s when we diagnose it,” said Jackson. “So it’s good to have your veterinarian look at it and have a culture done.”

Treatment for ringworm generally involves treating the whole horse–not just the area with ringworm. In a normal, healthy horse, ringworm is self-limiting, which means the horse will recover without treatment in two to three months.

“We recommend treatment to prevent spread to other horses, or to your dogs and cats, or yourself,” said Jackson.

Your veterinarian will likely prescribe a fungicide wash. An alternative home remedy consists of rubbing strong tincture (7 percent solution) of iodine into the lesions, using a piece of rough cloth to remove any scabs and to help the iodine penetrate the skin.

Tincture of iodine is quite caustic, however, and you should take care to not get it on healthy areas of skin. Another remedy that’s not as caustic is to apply a mixture of household bleach and water (50 percent solution) to the lesions. Use a 10-percent bleach solution to soak all grooming tools and washable tack that’s been in contact with the affected horse. Soak for several hours, then rinse.

Girth Itch

A body wash with a prescription fungicide will also resolve fungal infection in the girth area, also known as girth itch. This infection occurs when abrasions in the skin from the girth open the way for spores to invade.

Girth itch can usually be prevented by using a properly fitted, non-abrasive girth, and not using the same girth or grooming tools on more than one horse–to avoid spread of the fungus from one horse to another.

Another effective remedy for girth itch is Captan (the garden fungicide). Add water to the powder, according to instructions, and apply to the affected areas or as a body wash.

Bacterial Infections

Like fungal spores, bacteria also causes skin problems, although they’re generally not as contagious because they primarily affect the hair follicles.

“They might enter the follicles just because the horse has another problem; the horse might be itchy and breaks the skin by rubbing, allowing bacteria to enter,” said Jackson. “Or the skin may become moist and macerated [softened] and broken–and bacteria can enter. This type of infection may result in patchy hair loss or crusting.”

Occasionally, pus forms. Treat a mild, bacterial skin infection topically by washing with an antiseptic like chlorhexadine (Nolvasan). If it’s more severe, Jackson suggested systemic antibiotics.

Rain Rot

Stephen White, a veterinary dermatologist at the University of California-Davis, said one type of common skin infection is dermatophilosis, often called rain rot or rain scald. It’s an actinomycetes, which behaves like both bacteria and fungi. Dermatophilus congolensis may be spread from horse to horse by direct contact or by a carrier animal on the property, or by infected crusts in the environment, such as the soil of a pasture or paddock.

“The [organism] can probably live in the crusts for long periods of time,” said White.

If you have a rainy period, even if it’s only in spring or fall, you may notice crusts along the horse’s back, sometimes in a pattern where the back has been wet. Rain rot may also involve the legs, if the horse has to stand in mud or water. The crusts are not itchy, but they’re painful to the horse if you try to remove them.

The organism dermatophilus congolensis can be cultured for diagnosis.

“This infection responds well to antibiotics, given systemically. Sometimes a combination of penicillin and streptomycin is used, or potentiated sulphonamides. Mild cases are often treated topically with organic iodides, like an iodine shampoo,” said White.

Scratches

Scratches, greasy heel, cracked heels, dew poisoning and other terms are used to describe inflammation in the lower legs that’s generally caused by bacterial invasion of the tissues, often in conjunction with a fungus.

The inflammation can also be caused by mites, contact allergies (walking through plants, certain types of bedding, or other materials that cause irritation), dermatophilus or photosensitivity.

Unpigmented skin is more prone to inflammation because it’s not as tough and resilient as darker skin. White socks, for instance, are also more prone to photosensitization.

“Proper diagnosis [and proper treatment] depends on the owner being able to give the vet a good history on how long the disease has existed, which legs are affected and where, if there are other animals in that barn or pasture affected,” said White.

You may have to use presumptive treatments, such as topical medications effective against bacteria and fungi, or have your veterinarian take bacterial or fungal cultures, or even a biopsy, to identify the exact infective agent.

The affected areas must be kept clean and dry to promote healing. If the problem was caused by walking through mud, the horse should be relocated to a dry environment, if possible. If you catch scratches early, a topical antibiotic/fungicide applied daily will often heal most cases unless the problem is caused by something like mites, allergic reaction or photosensitization.

An excellent home remedy for scratches consists of mixing one part antibiotic ointment/cream (such as a wound dressing), one part DMSO (dimethyl sulfoxide, obtained from your veterinarian) and one part dewormer paste containing a benzimidazole drug. These oral dewormers are also good fungicides.

The DMSO reduces swelling, pain and inflammation and also helps the fungicide penetrate the area more deeply, taking it into the underlying tissues. The antibiotic cream combats any bacterial infection, and the deworming paste kills the fungus.

A word of caution, though. Do not use harsh chemicals, such as iodine, which is poisonous when taken internally, in conjunction with DMSO.

The dewormer, however, is safe to combine with DMSO because it’s intended for oral use. Applied daily (after first scrubbing and drying the affected area), this mixture will soon eliminate even a severe case of scratches. Bandaging isn’t necessary, however, and is actually detrimental because it’s better for the area to dry.

Warts

Viruses can occasionally cause skin problems, such as warts, which may appear on several parts of the horse’s body.

“We see different types of warts on horses,” said Jackson. “One is called aural plaque, found inside the ears–on the inner surface of the ear itself. These warts are spread from flies biting inside the ears. These warts are small, white lesions that look like cauliflower. They don’t seem to bother the horse, unless they become infected. This type of wart rarely resolves on its own. There’s no effective way of eliminating them, and we don’t get very concerned about them since they don’t bother the horse.”

Warts around the muzzle, by contrast, are self-limiting and will eventually disappear. These warts are usually seen in young horses that haven’t yet developed immunity to the virus that causes them. These usually run a course and then spontaneously resolve.

“We don’t worry about these warts unless they interfere with function, such as around the nostrils or in the mouth–where they interfere with eating or swallowing,” said Jackson.

Fly Bites

Some of the most troublesome skin problems are caused by bites of gnats or no-see-ums (various species of Culicoides). Their bites can cause allergic reactions and itching, often affecting the underline or the back. The itching reaction is called sweet itch, summer itch, seasonal dermatitis or Queensland itch.

“There isn’t a cure for this; the best thing to do is prevent it by using a fly repellent containing permethrin. In severe cases, a veterinarian will treat the horse with corticosteroids to shut down the allergic response,” said White.

Protecting the horse early in the season is much better than having to deal with it after the horse develops a reaction.

Fly repellent should be applied daily. To protect horses more completely, you can stable them, using small mesh netting on barn windows. Fans in stalls can also help since gnats are not strong fliers. If there’s a breeze, they can’t fly against it, noted White.

Parasites

“The most common type of mite-cased mange in horses is choriopic mange; we often see these mites in draft horses with abundant feathering,” said Jackson. “The mites live at the base of the long hairs. The horses get very itchy and will stamp their feet or rub the lower legs on objects. This problem is contagious between horses, by direct contact, or grooming tools.”

The mites don’t survive long in the environment, however, they’re spread through infected bedding. Treatment is usually topical and consists of a prescription from your veterinarian–a drug created specifically to kill mites.

The commonly used insecticides for flies usually won’t kill mites. To be most effective, you should first clip all the hair from the horse’s lower legs before applying the medication, and then thoroughly saturate the animal with it. Two treatments, two weeks apart, are generally needed, and all animals in the paddock/pasture should be treated to prevent reinfestation.

Biting and sucking lice also cause itchiness. Horses are susceptible to other parasites, but lice and chorioptic mange are most common.

“Deworming with ivermectin will rid a horse of biting lice, but the chewing lice are less affected,” said Jackson. “Often, you have to use a topical insecticide to kill those.”

The horse should be washed, sprayed or dusted with an appropriate insecticide (a delousing powder or an insecticide spray approved for killing lice). If weather is cold, use the powder and try to cover the entire animal. Wetting the entire horse with spray/dip is generally more effective, soaking the horse to the skin. Allow it to dry on the animal and don’t rinse. Wear rubber gloves or disposable plastic gloves to avoid getting insecticide on your skin. Repeat the treatment in two weeks to kill lice that hatched from eggs left on the hairs after the first treatment.

Photosensitivity and Hives

Sometimes sensitivity issues are triggered by certain feeds or plants. St. John’s wart, for instance, can cause photosensitization–creating a reaction in the skin after the photodynamic agent in the plant is absorbed into the bloodstream from the digestive tract.

Blood circulation carries it to skin, where it reacts with sunlight (especially in unpigmented skin that has little protection from UV rays) and creates a chemical change that sets up an inflammatory reaction, killing the skin cells.

Most horses with photodermatitis have a problem only on the white areas of their body, according to David Cross, DVM, PhD, clinical assistant professor at the University of Missouri. Sometimes the redness is just sunburn, but if the inflammation is deep in the skin layers, it may be more serious.

“When we see a horse with red, peeling skin on the face or muzzle, we tell the owner to apply zinc oxide [the ointment lifeguards wear], but if it’s a photosensitivity from something the horse has eaten, they should remove the horse from the pasture or feed that caused it,” said Cross.
The affected skin may slough off, leaving large raw areas. The horse should be kept out of the sun, and zinc oxide applied to the raw areas, until healed.

“Dermatitis and photosensitivity can be caused by a number of things, including something that was put on the horse, touched by the horse [such as nettles] or eaten by the horse. Sometimes there’s itching along with the swelling and redness,” said Cross.

Often, the only way to discover the cause is by process of elimination.

If you suspect it might be a fly spray, don’t use it. You may have to keep detailed records about everything you use on the horse or feed him to get a true picture of what might be causing the problem. A horse might have a reaction to something like fly spray, and it might not be noticed right away.

“Then you may see areas that are swollen or raised, hives or small water blisters in the skin. These may erupt and have the potential for scarring,” he said.

Reactions and problems elsewhere in the body often show up in the skin too.

“An internal illness can also affect the skin, making it drier than normal, or more dull and scaly,” said Jackson. “The skin condition will improve when the horse recovers from the illness.”

Any time a horse has hair loss, skin swellings or itchiness, it’s wise to have your veterinarian examine the horse for proper diagnosis and treatment. A severe case of hives may need treatment with corticosteroids–an injection of dexamethasone, for instance–to help relieve the swellings.

General Terms

There are many types of skin problems that are lumped together under blanket terms like dermatitis, scratches or dandruff.

Dermatitis simply means inflammation of the skin. The inflammation may be due to allergy or infection–sometimes secondary to trauma and injury, especially if the horse is rubbing and itching for some other reason and breaks the skin.

Scratches is a term that merely describes the location of the lesion (lower leg) and may be caused by bacteria or fungi or a combination of both. This term is misleading because many people think it’s a diagnosis–a specific condition–when in reality it just describes the type and location of the skin lesion.

Dandruff is a generic term, referring to flaky skin–which may be caused by a nutritional problem, such as an insufficient amount of fatty acids in the diet, or some other condition such as systemic illness or allergies from flies or other insect bites.