Horse skin diseases are one of the most common health challenges facing horse owners. The skin is the largest organ in a horse's body and acts as the first line of defence against bacteria, parasites, allergens, and environmental damage. When something goes wrong, the signs are usually visible — hair loss, crusting, swelling, itching, scabs, or unusual lumps.
The tricky part is that many horse skin conditions look remarkably similar to one another, which makes accurate identification essential before you reach for any treatment. Applying the wrong product can make things worse. This guide covers the most common horse skin diseases you are likely to encounter — bacterial, fungal, parasitic, allergic, and tumour-related — explaining what each one looks like, what causes it, and how it is treated.
Table of Contents
Bacterial Skin Diseases in Horses
Bacterial infections are among the most frequently seen horse skin diseases, particularly during wet or humid seasons.
Rain Rot (Rain Scald)
Rain rot — also called rain scald or streptothricosis — is caused by the bacterium Dermatophilus congolensis. It thrives in persistently wet conditions, which is why it tends to flare up during rainy seasons or when horses are left under damp blankets.
The signs are distinctive: raised, crusty scabs with matted tufts of hair that peel off in clumps, leaving small round bald patches underneath. You will usually find these lesions along the topline, shoulders, and hindquarters — anywhere that rain runs off the body.
Rain rot typically resolves within 14 to 21 days if the horse is kept dry. Treatment involves medicated shampoo containing chlorhexidine, removing loose scabs gently to expose bacteria to air, and keeping the horse out of wet conditions. Antibiotics are reserved for severe cases. For a deeper breakdown of the bacterium, lesion stages, and recovery, see our full guide to equine rain scald (dermatophilosis).
Pastern Dermatitis (Scratches, Mud Fever or Greasy Heel)
Pastern dermatitis goes by many names — scratches, greasy heel, mud fever, and cracked heels. It presents as redness, flaking, and crusting on the back of the pasterns, typically on the lower legs. Horses with heavy feathering on their legs, such as Clydesdales and Shires, are particularly prone.
The condition is caused by a combination of prolonged moisture, skin irritation, and bacterial overgrowth. Treatment involves clipping the area, keeping it clean and dry, and applying topical antibiotics or antifungals. A thin layer of barrier cream like petroleum jelly can help prevent recurrence once the condition has cleared. Read our complete guide to equine mud fever and pastern dermatitis for prevention strategies through wet winters.
Cellulitis
Cellulitis is a serious bacterial infection that develops in the tissue beneath the skin, usually after a small wound, joint injection, or bout of pastern dermatitis allows bacteria to penetrate. It most commonly affects one hind leg at a time.
The affected limb swells rapidly, becomes hot and painful to the touch, and the horse may be unwilling to bear weight on it. Fever and lethargy are common. Cellulitis requires prompt veterinary attention — treatment includes antibiotics, anti-inflammatory pain relief, hydrotherapy, and bandaging. Some cases do not resolve fully, and the condition can recur.
Fungal Skin Diseases in Horses
Ringworm (Fungal Dermatitis)
Despite its name, ringworm has nothing to do with worms. It is a fungal infection, usually caused by Trichophyton equinum or related species, that consumes keratin in the hair and skin. It spreads easily between horses through shared tack, grooming tools, and fencing, and it can infect humans as well.
Ringworm appears as circular patches of hair loss with crusty, scaly skin. The lesions are most common under the saddle and girth area, on the neck, and on the face, though they can appear anywhere. Affected areas may or may not be itchy.
Treatment involves isolating the horse immediately, clipping around the lesions, and applying antifungal shampoos or topical treatments. All tack and equipment that came into contact with the horse must be disinfected. Always wear gloves when handling an infected horse. Ringworm can resolve on its own, but treatment speeds recovery and limits spread. Our dedicated guide to equine ringworm (dermatophytosis) covers diagnosis and disinfection in detail.
Parasitic Skin Diseases in Horses
Mange
Mange is caused by tiny mites that burrow into or live on the skin. The most common type in horses is chorioptic mange, caused by Chorioptes equi, which typically affects the lower legs of horses with feathering. Signs include intense itching, small bumps, hair loss, and thickened or scaly skin. If left untreated, mange can cause permanent scarring that affects joint movement.
Treatment involves topical antiparasitic products containing lime-sulphur, permethrins, or organophosphates, applied several times at 12- to 14-day intervals to catch newly hatched mites. Oral ivermectin or moxidectin may also help. All horses that have been in contact with the affected animal should be treated simultaneously. See our guide to equine flea and mite infestations for more on identifying and clearing these parasites.
Lice (Pediculosis)
Lice infestations cause intense itching, leading horses to rub their skin raw — most noticeably on the shoulders, neck, and base of the mane and tail. Part the hair in good light and you may spot flat insects up to four millimetres long, along with pale eggs attached to nearby hairs.
Two types affect horses: chewing lice, which feed on dead skin cells, and biting (sucking) lice, which feed on blood. Severe infestations can cause anaemia. Treatment involves permethrin sprays, insecticidal shampoos, or powders, applied twice with a two-week gap to catch hatching eggs. Ivermectin targets sucking lice only.
Summer Sores (Habronemiasis)
Summer sores are caused by the larvae of gastric worms — Habronema muscae, Habronema majus, and Draschia megastoma — that are deposited on the skin by flies. The larvae cannot complete their life cycle in skin tissue, so they cause irritation instead.
Lesions appear as itchy, ulcerated, fleshy masses that bleed easily, often near wounds, the eyes, or the genitals. They are most common in warm, humid climates and tend to disappear in cooler months. Treatment includes topical anti-inflammatories, macrocyclic lactones, and fly control. Because flies spread the larvae, robust horse fly control is central to prevention — our guide to equine summer sores goes further on management.
Allergic and Immune-Related Skin Diseases in Horses
Allergic conditions are behind many of the itchy skin problems horse owners search for. They are rarely contagious, but they can be intensely uncomfortable and tend to recur seasonally.
Sweet Itch (Insect Bite Hypersensitivity)
Sweet itch is the most common allergic skin disease in horses. It is caused by an overreaction of the immune system to proteins in the saliva of Culicoides midges (biting insects). Icelandic horses exported to other countries appear to be most severely affected, though any breed can develop the condition.
The main signs are intense, persistent itching — especially along the mane, tail base, and withers — leading to self-inflicted wounds and hair loss from rubbing.
Management focuses on prevention: use specialist sweet itch rugs with permethrin coatings, stable the horse at dawn and dusk when midges are most active, and turn affected horses out in windier paddocks away from standing water and muck heaps. Glucocorticoids such as oral prednisolone can reduce itching once skin changes have occurred. Antihistamines offer variable results but hydroxyzine hydrochloride is considered one of the more effective options. For a full management plan, see our guides to insect bite hypersensitivity (sweet itch) and the closely related summer seasonal recurrent dermatitis (SSRD).
Hives (Urticaria)
Hives appear suddenly as raised, soft swellings over the abdomen and sides of the horse. They can be triggered by allergens in food, pollen, detergents on saddlery, or even heat. Horses are particularly prone to urticaria compared to other domestic species.
A single dose of dexamethasone is the standard first-line treatment. For recurrent cases, intradermal skin testing can help identify specific allergens, making allergen-specific immunotherapy a possibility.
Eosinophilic Granulomas
These small, firm, non-painful nodules most commonly appear along the neck, back, and withers during spring and summer. They are thought to result from an immune overreaction — often to insect bites or chemicals in saddle pads — that causes collagen breakdown in the middle layer of the skin.
The nodules are harmless unless they interfere with tack. A veterinarian can inject corticosteroids directly into the nodules to shrink them. If three or more injections at two-week intervals fail to resolve the issue, surgical removal may be recommended. Once calcified, the nodules become more difficult to treat. Our guide to equine eosinophilic granuloma explains the diagnosis in more depth.
Skin Tumours in Horses
Sarcoids
Sarcoids are the most common skin tumour in horses. They are associated with bovine papillomaviruses (BPV1 and BPV2) and tend to develop in areas where biting flies are active — the face, lower legs, neck, and underside of the abdomen. Sarcoids affect roughly 10% of the equine population.
There are five types: occult (flat, grey, scaly patches often confused with ringworm), verrucose (wart-like), nodular (lumps under the skin), fibroblastic (fast-growing, fleshy masses — the most common type), and mixed. They are not malignant, meaning they do not spread to internal organs, but they can be locally invasive and prone to recurrence after treatment.
No single treatment is 100% effective. Options include surgical excision, cisplatin injections, topical treatments, and cryotherapy. In some cases sarcoids resolve on their own. If a sarcoid is near the eye or in a high-friction area, treatment is generally recommended sooner rather than later, as fly activity and trauma can worsen the lesion. Our detailed guide to equine sarcoids breaks down each type and its treatment options.
Melanoma
Melanoma is most commonly seen in grey horses — an estimated 80% of grey horses will develop melanomas by 15 years of age. The tumours typically appear as black lumps under the tail, around the anus, or on the sheath of geldings.
Most begin as benign growths but can become malignant over time. At least 66% of equine melanomas are thought to eventually become cancerous. Treatment options are limited. Surgical excision is viable for early-stage tumours in accessible locations, and cisplatin injections can reduce tumour size. Grey horse owners should monitor their horses regularly for new or enlarging masses — our guide to equine melanoma in grey horses explains what to watch for.
Squamous Cell Carcinoma (SCC)
SCC accounts for around 20% of all equine skin tumours and is most common in horses between 12 and 16 years of age. It frequently develops around the eyelids, penis, and perianal region. Appaloosas and Paint horses show a higher predisposition. UV light exposure plays a role in ocular SCC, while papillomavirus is associated with penile SCC.
Lesions appear as non-healing, ulcerative wounds that worsen progressively. Early treatment with surgical excision and chemotherapy offers the best outcome. In horses with widespread spread, euthanasia may be the most humane option. See our guide to equine squamous cell carcinoma for diagnosis and prognosis.
Other Notable Horse Skin Diseases
Warts (Papillomatosis)
Warts are caused by the equine papillomavirus and most commonly affect young horses under three years of age, appearing on the muzzle, around the eyes, and occasionally on the ears and lower legs. They look like small, cauliflower-like pink or grey growths.
In most cases they resolve on their own within three to four months as the horse's immune system matures. Warts that interfere with eating, tack, or vision can be removed surgically or with laser treatment.
Photosensitisation and Sunburn
Horses with pink, unpigmented skin — particularly on the muzzle and lower legs — are prone to sunburn. This can be prevented with zinc oxide barrier creams or high-factor sunblock.
Photosensitisation is a more severe condition where the skin becomes dangerously sensitive to sunlight, typically caused by ingestion of certain plants (such as St John's wort) or underlying liver disease. The result is painful, red, crusting, and eventually sloughing skin on white or lightly pigmented areas. Blood tests should be run to rule out liver involvement. Affected horses must be kept out of the sun, and a titanium dioxide or zinc oxide cream applied to affected areas.
Pemphigus Foliaceus
Pemphigus foliaceus is the most common autoimmune skin disease in horses. The immune system mistakenly attacks proteins that bind skin cells together, causing small fluid-filled blisters that quickly rupture, leaving behind scaly, crusty lesions with hair loss. Swelling of the limbs and pain are also common.
It is diagnosed by skin biopsy and treated with glucocorticoids, typically over several weeks to months. Some cases resolve on their own without intervention.
HERDA (Hereditary Equine Regional Dermal Asthenia)
HERDA is a genetic condition found primarily in American Quarter Horses, particularly cutting horses. A defect in the collagen fibres of the skin causes the outer and inner skin layers to separate, resulting in fragile, easily torn skin that heals slowly and leaves disfiguring scars.
Signs typically appear around age two when a saddle is first applied. There is no cure, and the condition is inherited in an autosomal recessive pattern — genetic testing before breeding is strongly recommended. Read more in our guide to hyperelastosis cutis (HERDA).
When to Call a Veterinarian
Any skin condition that does not improve after a week of appropriate treatment, continues to spread, causes significant discomfort, or involves swelling and lameness warrants a veterinary call. Many horse skin diseases share overlapping symptoms, and a wrong diagnosis means a wrong treatment. Your vet can confirm the cause through skin scrapings, cultures, biopsies, or blood tests and put together a targeted treatment plan. Welfare charities such as Blue Cross and World Horse Welfare also offer useful owner guidance.
Early action generally leads to better outcomes. Skin problems that are caught and treated in the initial stages are far easier — and cheaper — to resolve than those that have been allowed to progress. Pairing prompt treatment with good day-to-day horse care — regular grooming, clean rugs, dry standing, and effective fly control — is the single best way to keep the most common horse skin diseases at bay.
