Strange lumps, itching, bald spots, redness, skin flaking, and scruffy patches are common signs of skin problems in horses.

While most equine skin irritations don’t present serious health risks, persistent skin problems can lead to infections and could indicate allergies, systemic inflammation or other health concerns. [1]

Identifying the underlying cause of skin issues is key to alleviating symptoms and preventing recurrence. Bug bites, mud, poorly fitted tack, bacteria and fungi are all common causes of dermatological issues in horses.

This article will review the identification, causes, treatments, and prevention of common skin irritations in horses. We will also discuss how to support equine skin health and manage horses with skin problems.

Common Equine Skin Problems

Equine skin irritations can arise from several different causes, including allergies, parasites, trauma, burns, chemical irritants, or diseases caused by bacterial infections, viral infections, fungal infections, parasites, or allergies. [1]

Skin problems are usually accompanied by dermatitis – a general term that describes skin inflammation. Other signs of irritation include:

  • Hair loss and bald spots
  • Bumps or hives
  • Thickened skin
  • Scaling or dandruff
  • Skin redness
  • Itching and discomfort
  • Skin lesions with or without fluid discharge

Early identification is vital for the effective management of many equine skin diseases. Horses with skin inflammation are at risk of secondary bacterial infections if the skin’s immune barrier function is compromised.

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Causes of Skin Irritations

Here are some common skin conditions that horse owners should learn to recognize.

Rain Scald

Rain scald, or rain rot, is a bacterial skin infection that affects the horse’s rump and back. Dry and scaly skin is the first symptom. In advanced cases, horses develop crusty lesions and scabs with upright tufts of hair. [2]

Under the scabs, raw skin may discharge sticky yellow exudate. The secretion causes hair to matte together. Bald spots and areas of hair loss occur when scabs detach from the skin. [3]

This type of dermatitis can also affect areas of the barrel, shoulders, hindquarters, face, and lower legs.

Causes

Rain scald is caused by the bacteria Dermatophilus congolensis. This opportunistic organism is naturally present on the skin and multiplies rapidly in a moist environment. [2]

When excessive moisture weakens the skin’s protective barrier, the bacteria invade the epidermis and result in infectious lesions. [2]

Treatment

The horse’s skin must remain dry while being treated for rain scald. Allowing the coat to dry out will reduce recovery time and aid the healing process.

Washing the skin with chlorhexidine scrub and soaking it in a saline solution helps remove crusty skin. Some local lesions respond to treatment with topical silver sulphadiazine. In rare cases, your veterinarian may prescribe systemic antibiotics. [2]

Rain scald lesions usually heal without scarring. Mild cases usually subside within two to three weeks.

Prevention

Horses that live outside in wet conditions have a higher risk of rain scald. Always ensure horses have access to adequate shelter and consider stabling your horse to let their coat dry. Waterproof blankets can also protect horses from excess moisture during turnout. [2]

Rain scald is contagious. Regularly disinfect equipment that contacts an affected horse and avoid sharing brushes with other animals to prevent infection.

Pastern Dermatitis

Also known as scratches, mud fever, or greasy heel, pastern dermatitis refers to multiple conditions that cause skin irritation on the horse’s pastern.

Mild forms of pastern dermatitis cause redness, itchiness, and hair loss. More severe cases involve skin lesions on the pastern and heel that produce oily secretions. [4]

These clinical signs can progress to tissue granulation or proud flesh. Horses with advanced pastern dermatitis can experience significant pain and become lame. [4]

Causes

Pastern dermatitis has multiple causes, but microbial infection is the most common. Several strains of bacteria are associated with the conditions, including Dermatophilus congolensis. [5]

Other infectious causes of pastern dermatitis include soil-borne fungi and parasites. Parasitic mites associated with pastern dermatitis damage the skin and allow pathogenic microorganisms to enter. [4]

Underlying health conditions can also predispose horses to pastern dermatitis by weakening the horse’s skin barrier and immune system. [4]

Treatment

Veterinarians must first identify the root cause of pastern dermatitis to recommend an effective treatment. They may collect skin samples to test for bacteria, fungi, or parasites. Blood tests can help rule out underlying health conditions. [4]

Effective treatments for pastern dermatitis aim to stop the source of infection or skin damage, allowing the skin to heal. Treatment typically involves applying topical medications to affected patterns.

Depending on the diagnosis, your veterinarian may recommend an antibacterial, antiparasitic, or antifungal cream. [4]

Prevention

Risk factors for pastern dermatitis include wet conditions, sandy footing, dirty bedding, incorrect bandaging, insect bites, and thick pastern hair. [4]

Horse owners can help prevent pastern dermatitis by keeping the lower legs as clean and dry as possible. Limit exposure to muddy conditions in turnout and dry legs thoroughly after bathing to avoid excessive moisture weakening the pastern skin.

Abrasive substances can also irritate the pastern skin. Wash work boots and thoroughly clean your horse’s legs after riding in a sandy arena to avoid skin irritation.

Ringworm

Ringworm, or dermatophytosis, is a highly contagious and relatively common skin disease in horses. This disease affects the hair and epidermis.

The first sign of ringworm is a change in the angle of the hair shaft. The altered angle creates small, often circular, patches of hair that stand out from the rest of the coat. [6]

Eventually, hair loss reveals round patches of scabby, crusty skin. These lesions are common on the chest, neck, shoulders, and face. But ringworm can occur anywhere on the body. [6]

Causes

Ringworm is a fungal infection generally caused by organisms in the Trichophyton and Microsporum families. These fungi are dermatophytes that consume keratin, a protein in hair and skin cells. [6]

Fungal spores can survive for extended periods in barn environments, and transmission occurs when horses come in contact with contaminated materials. Infection usually occurs in areas of minor skin damage where fungi can multiply rapidly. [6]

Treatment

Active ringworm infection requires treatment to limit the spread of the disease. If you suspect your horse has ringworm, immediately isolate him from all other animals. Equine dermatophytes are zoonotic and can cause infection in dogs, cats, and humans. [6]

Topical treatment with antifungal shampoos and ointments can prevent the progression of lesions and limit spore production. Clip hair and gently remove scabs around the lesion before treatment to reduce the organism’s food source. [6]

If lesions continue to spread, contact your veterinarian. They can confirm a ringworm diagnosis and prescribe oral medications if necessary.

Prevention

Keep separate equipment, tack, and grooming supplies for every horse to limit transmission of ringworm and other contagious diseases. Cleaning the stable with disinfectant can also kill any spores in the environment. [6]

Sweet Itch

Insect bite hypersensitivity, also known as sweet itch, is an allergic reaction that causes severe itching, skin lesions, and hair loss in horses. This chronic seasonal disorder is challenging to manage and can cause significant discomfort for the horse.

Skin lesions commonly occur at the base of the mane or tail. They can also form on the horse’s sides, belly, legs, or head. These lesions may swell, bleed, or appear crusty. They are often hairless and sometimes non-healing. [7]

Many horses aggressively scratch themselves to relieve itchiness. Rubbing causes skin damage, which can lead to secondary infections. [7]

Sweet itch is a common equine allergic condition affecting approximately 10% of all horses worldwide. [8]

Causes

An allergy to bites from insects in the Culicoides genus causes sweet itch. These insects are commonly called midges. [9]

Allergies are immune disorders arising from an abnormal immune reaction to a foreign substance or allergen. When midges bite an affected horse, their salivary proteins activate allergen-specific antibodies, including immunoglobulin E (IgE). [10]

IgE binds to the salivary proteins and initiates the release of histamine and prostaglandins, resulting in itchiness for the horse. [10]

Treatment

There is currently no cure for sweet itch. Most treatment strategies aim to improve the horse’s comfort by relieving itching symptoms. Some practitioners use steroids, but these treatments have a low success rate and carry a risk of adverse side effects. [12]

Recent research supports new vaccines as potential therapeutic agents. The IL-5 vaccine targets eosinophils, major inflammatory cells in sweet itch lesions. Studies found that active IL-5 cytokine decreased lesion severity. [8]

IL-31 is similar to the IL-5 vaccine but affects a different cytokine responsible for itching. Clinical trials show active vaccination reduces symptoms in affected horses but won’t prevent the allergic reaction. [13]

Prevention

Genetic and environmental factors determine a horse’s risk of developing sweet itch. Some research on Icelandic horses suggests that early exposure to Culicoides species can reduce future sweet itch episodes. [14]

Most prevention strategies aim to stop midges from coming in contact with horses. Stabling horses from dusk to dawn in hot, humid conditions when midges are most active can limit exposure. [15]

Insect protection with topical repellents, mesh sheets, fly masks, fly boots, and proper manure management can also help prevent sweet itch. [15]

Identifying Other Equine Skin Problems

If your horse’s symptoms don’t fit the clinical signs for the common skin irritations above, he may have a different condition. Horses can experience a variety of skin diseases caused by other allergic reactions, viral infections, parasitic infections, and skin tumours.

Allergic Reactions

Unusual bumps on your horse’s skin can indicate an allergic reaction to something in the environment or to components of their diet.

Hives are skin eruptions of localized dermal swelling resulting from insect bites, medications, or allergen exposure. Identifying and eliminating the triggering factor will resolve the hives. [16]

Small, firm nodules on the neck, back, and withers may be eosinophilic granulomas. These bumps are caused by allergy-driven collagen breakdown in the middle layer of the skin. The nodules are harmless, but veterinarians can use steroid injections to shrink them. [17]

Viral Infections

Equine papillomavirus can cause warts in horses. These cauliflower-like growths often appear on the muzzle of young horses without resistance to the virus. The warts are harmless and typically disappear within about four months. [18]

An equine papillomavirus spread by biting flies can cause crusty, raised white lesions inside your horse’s ears. These aural plaques usually don’t resolve on their own, but treatment is not recommended unless the horse starts resisting having their ears handled. [19]

Skin Tumors

Sarcoids are the most common skin tumour found on horses. These usually non-malignant tumours appear as round, flat areas of hairless, roughened skin. Sarcoids are not painful or itchy but can become aggravated by attempted surgical removal. [20]

Some skin tumours in horses require treatment to prevent them from becoming malignant. Melanomas are most common in grey horses and usually occur around the rectum and tail head. [21] Squamous cell carcinoma is generally found around the eyes and penis. [22]

Parasitic Infections

Several types of mites can cause mange in horses, characterized by bald spots, scaly skin, and itchiness. The infection can cause permanent skin damage without prompt treatment. [23]

While relatively uncommon, horses can also suffer from lice. This parasitic infestation is very uncomfortable and may result in anemia. Horse owners often notice hair loss from rubbing on the affected areas and find pale eggs attached to nearby hair. [24]

Support Skin Health

Skin problems in horses are rarely just skin-deep. Persistent skin diseases can indicate a compromised immune system resulting from other diseases, advanced age, gut issues, or poor nutrition. [1]

Consult your veterinarian if minor skin irritations don’t respond to treatment or continue to recur. Your veterinarian will examine your horse for underlying conditions and recommend dietary or management changes to support skin health.

A balanced diet with adequate protein, antioxidants, vitamins, and minerals supports skin and hair coat quality. [25]

Nutrition

Dietary protein and zinc are important for immune function and are required to produce the enzymes and antibodies that fight infection. [26]

Antioxidants such as selenium and vitamin E work together to neutralize free radicals contributing to inflammatory disease.  [27]

Diets high in starches and non-structural carbohydrates (NSC) can contribute to inflammation. Consider reducing grains and switching to a low-NSC, forage-based diet. [28]

Research suggests that omega-3 fatty acid supplementation helps moderate the inflammatory response in horses. Studies in horses with sweet itch found that supplementing with flaxseed oil reduced skin lesions and inflammation. [29]

Mad Barn’s W-3 Oil is a fat supplement that provides high levels of the omega-3 fatty acid DHA and natural Vitamin E to support skin health and coat quality.

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  • Promotes joint comfort
  • Helps to fight inflammation
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  • Palatable source of Omega-3's

Spirulina is another supplement that may benefit horses with skin allergies. This blue-green algae is a rich source of the anti-inflammatory omega-6 fatty acid gamma-linolenic acid. [30]

Studies show that spirulina can inhibit histamine release and decrease the production of pro-inflammatory antibodies. This effect helps decrease itchiness and reduce allergic overreaction in horses with skin issues. [31]

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Summary

  • Effective management of skin irritations in horses requires targeted treatment of the root cause.
  • Common skin problems in horses include rain scald, pastern dermatitis, ringworm, and sweet itch.
  • Allergic reactions, skin tumours, and infection from bacterial, viral, fungal, or parasitic sources can also cause skin problems in horses.
  • Persistent skin issues often indicate an underlying health condition or compromised immune system.
  • Proper nutrition supports skin health by promoting optimal immune function.

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References

  1. Wobeser, B. Skin Diseases in Horses. Vet Clin North Am Equine Pract. 2015. View Summary
  2. Pilsworth, R. et al. Dermatophilosis (Rain Scald). Equine Vet Ed. 2007.
  3. Burd, E. et al. Pustular dermatitis caused by Dermatophilus congolensis. J Clin Microbiol. 2007.
  4. Colles, C. et al. Equine pastern dermatitis. Equine Vet Ed. 2010.
  5. Aufox, E. et al. The prevalence of Dermatophilus congolensis in horses with pastern dermatitis using PCR to diagnose infection in a population of horses in southern USA. Vet Derm. 2018. View Summary
  6. Pilsworth, R. et al. Dermatophytosis. (ringworm). Equine Vet Ed. 2007.
  7. Quinn, P. et al. Sweet itch: responses of clinically normal and affected horses to intradermal challenge with extracts of biting insects. Equine Vet J. 1983. View Summary
  8. Fettelschoss, A. et al. Treating insect-bite hypersensitivity in horses with active vaccination against IL-5. J Allergy Clin Immunology. 2018. View Summary
  9. Anderson, G. et al. Culicoides obsoletus (Diptera: Ceratopogonidae) as a Causal Agent of Culicoides Hypersensitivity (Sweet Itch) in British Columbia. J Med Entomol. 1991.View Summary
  10. Wilson, A. et al. Detection of IgG and IgE serum antibodies to Culicoides salivary gland antigens in horses with insect dermal hypersensitivity (sweet itch). Equine Vet J. 2010.View Summary
  11. Jonsdottir, S. et al. New Strategies for Prevention and Treatment of Insect Bite Hypersensitivity in Horses. Vet Derm. 2020.
  12. Fettelschoss, A. et al. Molecular mechanisms and treatment modalities in equine Culicoides hypersensitivity. Vet J. 2021. View Summary
  13. Civitas, I. et al. Investigating the epithelial barrier and immune signatures in the pathogenesis of equine insect bite hypersensitivity. PLoS One. 2020. View Summary
  14. Björnsdóttir, S. et al. Summer eczema in exported Icelandic horses: influence of environmental and genetic factors. Acta Vet Scand. 2006. View Summary
  15. Coates, H. Dealing with sweet itch and other summer allergies in horses. Vet Times. 2017.
  16. Sauve, F. Can equine urticaria be cured? Can Vet J. 2020.View Summary
  17. Mathison, P. Eosinophilic Nodular Dermatoses. Vet Clin North Am Equine Pract. 1995. View Summary
  18. Hamada, M. et al. Histopathological development of equine cutaneous papillomas.. J Comp Pathol. 1990.
  19. Mira, J. et al. Frequency of Equus caballus papillomavirus in equine aural plaques. J Vet Diag Invest. 2018. View Summary
  20. Taylor, S. et al. A review of equine sarcoid. Equine Vet Ed. 2012.
  21. Moore, J. et al. Melanoma in horses: Current perspectives. Equine Vet Ed. 2012.
  22. Taylor, S. et al. A review of equine mucocutaneous squamous cell carcinoma. Equine Vet Ed. 2012.
  23. Osman, S. et al. Clinical and therapeutic studies on mange in horses. Vet Parasitol. 2006. View Summary
  24. Wright, R. Lice on horses. Can Vet J. 1999. View Summary
  25. Carr, E. et al.  Nutrition of Critically Ill Horses. Vet Clin North Am Equine Pract. 2009. View Summary
  26. Wagner, B. Immunoglobulins and immunoglobulin genes of the horse. Dev Comp Immunol. 2006. View Summary
  27. Baalsrud, K. et al. Influence of vitamin E and selenium supplement on antibody production in horses. Equine Vet J. 1986. View Summary
  28. Suagee, J. et al. Effects of High-Sugar and High-Starch Diets on Postprandial Inflammatory Protein Concentrations in Horses. J Equine Vet Sci. 2015.
  29. O’Neill, W. et al. Flaxseed (Linum usitatissimum) supplementation associated with reduced skin test lesional area in horses with Culicoides hypersensitivity. Can J Vet Res. 2002. View Summary
  30. Choopani, A. et al. Spirulina: A source of gamma-linoleic acid and its applications. J Appl Biotech Rep. 2016.
  31. Kellon, E. Use of the Herb Gynostemma Pentaphyllum and the Blue-green Algae Spirulina Platensis in Horses. Equine Congress. 2006.
  32. Moriello, K. Dermatitis and Dermatologic Problems of Horses. Merck Veterinary Manual. 2019.