Horses are prone to a number of different skin conditions and diseases. Some are minor and resolve on their own, while others can be much more serious.
Skin conditions may affect localized areas on the horse, such as the legs or abdomen, or they can be widespread, affecting multiple areas. Symptoms may include itchiness, swelling, hair loss, skin flaking, and more.
Learning to recognize various equine skin diseases is important to take the appropriate actions needed to resolve the problem or to manage the horse to keep them more comfortable.
In this article, we will discuss how to identify common infections and conditions affecting your horse’s skin, as well as treatment protocols. If your horse shows signs of a skin problem, consult with your veterinarian to obtain an accurate diagnosis.
Equine Skin Diseases
Skin is the largest organ of the horse’s body. Along with the hair coat, hooves, sweat and oil glands, it makes up the integumentary system.
One of the primary functions of the skin is to protect your horse from external factors such as bacteria, chemicals, and extreme temperatures. Skin also acts as an immunologic barrier and is often the first organ to come in contact with environmental allergens.
Skin is made of two layers: the outer, nonvascular epidermis and the inner, vascular and sensitive dermis. The horse’s epidermis comprises 5-7 cell layers, not including the horny layer of haired body skin.
The dermis supports many other structures in the body such as blood and lymph vessels, hair follicles, muscles, nerves, and glands. 
Horses’ bodies are covered in hair, adding further protection from outside factors. Diseases and conditions of the skin also commonly affect the hair, which horse owners typically notice first.
Below are some of the most common skin conditions seen in horses and signs you can use to identify these diseases in your horse.
Sarcoids are the most common skin tumor found in horses. They can also affect other equids including zebras, donkeys, and mules. Sarcoids are not cancerous, but they can be invasive and are seen as cosmetic defects. 
Sarcoids are usually associated with two types of bovine papillomaviruses, BPV1 and BPV2. However, some biopsied sarcoids are not associated with either virus, and the cause is unknown in those cases. 
Sarcoids can occur in horses of any age, but they are most common in younger horses. They usually appear on the head, limbs, neck, and shoulder but can form anywhere on the horse’s body. 
Sarcoids usually aren’t serious, but they can become ulcerated and infected. If they form near the eye, they can also impair the animal’s vision. 
Sarcoids can vary quite a bit in their appearance and there are five general types that exist in horses:
- Occult: Flat patch where hair is absent with a grey, scaly surface. Often circular in shape and commonly confused with ringworm. Usually occur on the face, neck, or between the back legs.
- Verrucose: Wart-like and scaly but extend deeper into the tissue than the occult sarcoid. Often irregular in shape, and multiple lesions may appear.
- Nodular: Lumps form under the skin and often appear shiny. These vary in size–some being more than 5 centimeters in diameter. Usually occur around the groin and eyelids.
- Fibroblastic: Usually a fast-growing, fleshy mass which can begin as a complication of a skin wound. Often become ulcerated and “hang” on a stalk. Can become extremely invasive into the surrounding skin. This is the most common type of sarcoid.
- Mixed: A variable combination of two or more types of sarcoids, often appearing at different times, forming a “colony”.
Sarcoids can be difficult to treat and may return after treatment. Because of this, they can be a frustrating condition for both veterinarians and horse owners. In some cases, however, sarcoids will resolve on their own. 
The most effective treatment for sarcoids is usually complete removal of the lesion and surrounding skin. Other treatments, including topical or injectable products, have been successful, but no treatment is effective in 100% of cases. 
This condition is characterized by lesions that form on the back of the pasterns and it can be severe in some cases. Pastern dermatitis can occur in any breed of horse, but is most common in draft breeds or other breeds with heavy feathering on the lower legs. 
Horses with pastern dermatitis may develop chronic wounds with persistent inflammation. Pastern dermatitis also tends to be a recurring condition. 
Treatment for pastern dermatitis will depend on the underlying cause. Clipping and cleansing the area, antibiotics, and topical corticosteroids are the most common treatments, however. 
Sweet Itch, also known as Queensland itch, summer eczema, summer dermatitis, or insect-bite hypersensitivity, is the most common allergic skin disease in horses.
It is most often caused by the Culicoides insect (often called midges) which inject salivary gland proteins into the horse’s skin when they bite. These proteins cause sensitization and allergies in predisposed horses. 
Horses with sweet itch have intense itching and often rub the affected area, resulting in open wounds and secondary infections. The mane, tail, and withers are most often affected. 
Most horse breeds are susceptible to sweet itch, but the prevalence varies from country to country. Icelandic horses exported to other areas appear to be most at risk for developing the condition. 
Sweet itch is notoriously difficult to treat. Treating this condition involves preventative measures such as protection from Culicoides by stabling the horse from dusk until dawn, and using special blankets, and insect repellents. Glucocorticoid therapy can be used as well. 
Streptothricosis is commonly referred to as rain rot or rain scald. This condition is characterized by oozing, crusty lesions and matted hair. It can occur not only in horses but in other mammals as well. Rain rot is most common in warm, humid areas with rainy seasons. 
The good news is that this skin condition often resolves within 14-21 days if the horse is kept out of the elements. However, some horses can develop chronic cases which result in hair loss and thick, crusty skin in affected areas.
Treatment of rain rot usually includes the use of medicated shampoo with chlorhexidine and keeping lesions dry until they resolve. Antibiotics may be used in severe cases. Researchers have also found that applying tea tree oil and other essential oils may improve afflicted areas. 
This common skin condition is characterized by non-cancerous lesions most often reported in spring or summer. They appear as raised, non-painful nodules with normal overlying skin usually forming in the saddle region or neck of the horse.
They can range from less than one centimetre to over ten centimetres in diameter. 
In rare cases, a horse may have large numbers of eosinophilic granulomas spread across the body. Surgical removal of lesions is the most common treatment. However, glucocorticoids injected into the lesions or given orally may also be effective. 
Melanoma is one of the most serious skin conditions affecting horses. It appears as a black lump or multiple lumps usually forming under the horse’s tail, around the anus, or on the sheath of geldings.
Most start out as benign (non-cancerous) but tend to become malignant or cancerous with aging. 
The two most common types of melanomas are dermal melanomas, which appear as small, individual tumors, and dermal melanomatosis, which appears as individual tumors that merge to create one large mass. 
Melanomas most often occur in gray-coloured horses. It’s been estimated that 80% of all gray horses will develop melanomas by 15 years of age.
These lesions may metastasize in the lymph nodes, liver, spleen, skeletal muscle, lungs, and blood vessels of gray horses. However, melanoma in solid-coloured horses tends to be more severe than in gray horses. 
Some sources say that at least 66% of all melanomas will eventually become malignant. Unfortunately, there is no widely accepted treatment for equine melanoma, but some can be successfully removed through surgery. For advanced cases, surgery may not be feasible, however. 
Owners of gray horses should have them regularly examined to identify new masses and evaluate tumor growth rate. 
Surgical excision is the best option for Stage 1 and 2 melanomas in locations that allow complete removal. A drug called cisplatin can be injected into tumors to reduce size. Other experimental therapies for equine melanoma are ongoing and may present the best option for horses with Stage 4 melanoma. 
Vitiligo is another common skin disease that most often appears in gray horses as well. This condition is considered an autoimmune disease and leads to depigmentation of the skin due to destruction of melanocytes.
Researchers estimate that vitiligo occurs in between 26-67% of gray horses, but it is also found in 0.8-3.5% of non-gray horses. There is no visible inflammation of the skin with vitiligo and there are no other symptoms. 
Chronic Progressive Lymphedema (CPL)
CPL is a serious and often disabling skin disorder in which the lymphatic flow in the horse’s legs becomes compromised. It occurs in draft breeds such as Clydesdales, Shire, and Belgians, beginning early and often worsening over time. 
Severe changes such as skin thickening and dermal fibrosis (injury to the skin) with thick skin folds and nodules usually occur. Secondary infections can make Chronic Progressive Lymphedema worse and add to the discomfort of the horse. 
CPL is a complex disease involving underlying genetic factors and triggers from the horse’s environment, including management practices. Stalling and lack of movement are factors that can trigger CPL. 
CPL cannot be cured but careful management and supportive therapy can help improve the horse’s quality of life. This may include:
- Antibiotics to treat secondary infections
- Anti-parasitic treatments for skin mites (which are common with CPL)
- Keeping the leg feathers clipped short
- Daily exercise
- Massage to encourage lymph drainage
Compression bandaging can also be helpful if done correctly. 
Ringworm isn’t typically severe, but it is one of the most common skin diseases affecting horses. This condition is caused by a fungus (usually Trichophyton equinum and Trichophyton mentagrophytes) which is often transmitted by shared tack, grooming supplies, or even clothing. 
Ringworm appears as an itchy, circular pattern of hair loss, which may also be red or appear like a rash. It usually occurs on the girth and saddle areas but can spread to other parts of the horse’s body. It some cases, ringworm resolves without treatment, but it will take a month or longer. 
Treating horses as soon as possible will help to limit discomfort and prevent the spread of the fungus to other animals or people. Ringworm is treated with anti-fungal shampoos or topical therapies. Tack, grooming supplies, and other potentially contaminated surfaces should be disinfected to prevent re-exposure. 
Warts are caused by the papillomavirus and can affect horses and many other animals. They are the most common skin tumor in horses, usually appearing on the lower limbs or face of younger animals.
The virus that causes warts is transmitted through open skin, and biting insects may carry it. Young horses between one and three years of age are most susceptible due to trauma and an immature immune system.
In the ears, warts may appear as large, white plaques sensitive to the touch. Fly bites in the ears may cause bleeding, and secondary bacterial or fungal infection is common. Horses with ear warts often need treatment and protection via a fly mask with ear covers. 
However, most warts don’t cause discomfort and often resolve themselves within three months. They can also be surgically removed for cosmetic reasons if the owner desires. 
Cellulitis is a potentially serious and frustrating condition that affects a horse’s limbs. It may have no known trigger or it may follow surgery, joint injections, wounds, or other types of trauma.
This condition is characterized by inflammation and infection in the tissues that lie just beneath the skin and usually affects one limb at a time, most often in the hind end. 
Cellulitis appears as severe swelling associated with lameness, with some horses refusing to bear weight on the affected limb. The condition usually develops rapidly and the affected limb is warm and painful to the touch. Fever and lethargy may also be present. 
Prompt diagnosis and treatment of cellulitis are very important to increase the chances of a successful outcome. Staphylococcus spp. is often found in the skin with cellulitis cases so antibiotics may be used as well as non-steroidal anti-inflammatories for pain and inflammation.
Hydrotherapy, bandaging, hand-walking, and lunging may all be helpful as well. 
Many cellulitis cases take a while to resolve. Sometimes, horses do not recover, making euthanasia the most humane option. 
Summer Sores (Habronemiasis)
Summer sores are caused by third-stage larvae of three different gastric worms that affect horses:
- Habronema muscae
- Habronema majus
- Draschia megastoma
The adult worms live in the horse’s stomach and the skin lesions are caused by migrating larvae which are transmitted by flies. 
Summer sores often appear on the limbs, chest, lower abdomen, around the genitals, or near the eyes of the horse. They become ulcerated masses that bleed easily, may be itchy, and/or may contain dead or calcified granules. A horse may have one lesion or several. 
Summer sores are most prevalent in tropical and subtropical areas of the world. Wounds often spontaneously disappear in the colder months and reappear when temperatures rise. Researchers aren’t clear if this is because larvae remain in the lesions in a dormant state. 
Lesions may heal on their own or become recurrent, non-healing masses which attract flies, leading to further infection.
Squamous Cell Carcinoma
Squamous cell carcinomas are a frequently diagnosed skin cancer in horses. They account for approximately 20% of all equine skin tumors. 
They can affect horses of any age but are most common in horses between 12-16 years of age.  Appaloosas and Paint horses appear predisposed to this condition, with males at a slightly increased risk over females.
Most squamous cell carcinoma tumors develop around the eyelid, penis, and perianal region. They appear as a solitary, ulcerative and non-healing wounds but as the disease progresses, there is often dead tissue around the area and a foul-smelling discharge. 
UV light exposure is believed to contribute to developing tumors on the eyelids. Papillomavirus seems to be associated with penile squamous cell carcinomas.
Areas of chronic inflammation such as burns or other non-healing wounds are possible sites for tumor development. 
Surgical excision of the tumor, along with chemotherapy, can resolve the disease, but this may not be possible in certain locations or with excessively large tumors.
Exuberant Granulation Tissue (Proud Flesh)
Leg wounds on horses can be difficult to treat because they cannot be sutured. As the body heals, granulation tissue forms and can become excessive, leading to a condition known as proud flesh.
It is easier to prevent this skin condition than to treat it once it has formed. To prevent proud flesh, keep wounds clean and have necrotic tissue debrided (by you or your veterinarian).
Pressure bandaging may also help to prevent the formation of proud flesh. But once granulation tissue has begun to form, bandaging may encourage its growth. Using silicone gel dressings can also help reduce the formation of proud flesh. 
Horses can develop autoimmune diseases that affect the skin and hair coat. Pemphigus foliaceus (PF) is the most common of these, appearing in horses from two months to over twenty years of age. 
This condition presents as small, fluid-filled sacs (vesicles) on the face or limbs that may spread to other body parts.
The vesicles do not remain on the skin long, but leave behind hair loss, scaling, and crusting lesions. Itchiness, pain, and limb swelling are common in many cases. 
Pemphigus Foliaceus is caused by the production of auto-antibodies to intra-epidermal adhesion proteins. It is diagnosed by culture and biopsy and is easiest to identify while the vesicles are still present.
Standard treatment is with glucocorticoid administration, but it often takes weeks or months to resolve. In some cases, the condition spontaneously resolves on its own. 
Hereditary Equine Regional Dermal Asthenia (HERDA)
HERDA, also referred to as hyperelastosis cutis, is a degenerative skin disease that occurs mainly in American Quarter horses, most commonly in cutting horses and pleasure/working-cow horses.
This genetic condition causes a defect in the collagen fibres of the skin, leading to the separation of the epidermis and dermis.  HERDA can cause disfiguring scars and loose and elastic skin in affected horses. 
Symptoms of HERDA usually start when the horse is around two when pressure from the saddle causes the skin to tear. This produces wounds that require prolonged healing time.
In this article we have listed some of the most common skin diseases and conditions affecting horses. Many have distinct symptoms, but some may mimic other conditions.
If you suspect your horse is affected by any equine skin disease, it is important to get your veterinarian involved right away to obtain a proper diagnosis and treatment plan. Early intervention can increase the likelihood of a successful outcome.
While many skin problems affected horses are not serious and resolve on their own or with minimal treatment, others require immediate veterinary attention.
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