Even the best-kept horses occasionally come down with a skin disorder. Horses that aren't well-kept, or are otherwise debilitated, are even more vulnerable. Some skin disorders can be life-threatening, such as the melanomas so common in gray horses. Fortunately, the majority of equine skin problems are temporary in nature and curable with proper medication, improved hygiene and nutrition, or tincture of time.
Bald spots in horses result from a variety of causes, including parasite infestation, fungal or bacterial infection, self-trauma or even a horse's normal shedding cycle. If accompanied by itching, it's more likely to occur because of infection, allergies or insects, but ill-fitting tack is often the culprit. Your horse might develop a skin reaction from any type of allergen, but the most common include shampoos, fly sprays, plants, liniments or any item touching his body. A definite diagnosis and treatment plan may depend upon your veterinarian's conducting a skin culture or biopsy.
Although rain rot appears more often in horses with weak immune systems, perfectly healthy outdoor equines frequently come down this bacterial infection after long periods of rain. You're most likely to find crusty rain rot scabs in areas where rain runs off a horse, such as the back, the hindquarters and the lower legs. The scabby areas soon lose hair. All sorts of over-the-counter remedies are available to treat rain rot. If the rain rot is severe, don't waste time with these commercial products -- call your vet. If the rain rot is mild, a commercial remedy might help, but contact your vet if the condition doesn't improve significantly within a day or two of application.
Ringworm is a zoonotic disease, meaning you can catch it from your horse. Hairless, circular lesions appear on the affected animal, and it easily spreads from one horse to another. It's more of a nuisance than anything else, but your vet can provide anti-fungal shampoos and topical medication to get rid of it. Wear gloves when treating an affected horse, and don't share his brushes, tack, blankets or similar items with other equines.
Equine skin cancer consists primarily of melanoma or squamous cell carcinoma. The latter often results from prolonged sun exposure in light-skinned horses and is more often found in hot climates. It initially appears as rough patches with lesions, usually on the genitals or nose. Melanomas consist of dark tumors, often growing on the rectum, the mouth, or the urinary or genital tract. Surgical excision is the treatment for both types of cancer.
Warts, or papillomas, usually appear on the muzzles, genitals or lower legs of young horses. Although unsightly, these cauliflowerlike growths aren't harmful and generally disappear within a few months without treatment. If a wart appears on an older horse or lasts for more than six months on a young animal, call your vet.