Why is My Horse Itchy? Pruritis Causes, Management & Related Conditions

Itching and scratching are common behaviors in horses. Spending much of their time living outdoors, horses are constantly exposed to the elements and pests. Scratching to relieve mild skin irritation is a natural part of healthy equine grooming and social interaction.

If itching, also known as pruritus, becomes persistent or leads to scratching severe enough to break the skin, it may indicate an underlying medical issue. Pruritus can be caused by various factors, including insect bites, parasite infestations, bacterial or fungal infections, and allergic reactions.

While pruritus is often not immediately concerning, it can be a sign of serious conditions like equine pythiosis. Additionally, excessive scratching can cause skin lesions that may become infected.

Recognizing the difference between normal and concerning itching is crucial for owners and caretakers to make effective management decisions and address health issues promptly.

Itching in Horses

Horses are housed outdoors worldwide, showcasing their hardiness and adaptability. With so many diverse climates across the world, equines are exposed to all manner of environmental conditions, each bringing its own mix of airborne, biological, and ambient factors that can affect their physical comfort.

Itching, or pruritis is a natural adaptation in mammals to defend against skin irritation. Horses routinely scratch themselves and each other to relieve mild skin irritation associated with their outdoor living conditions.

If you notice your horse itching or scratching themselves more than normal, it can be difficult to determine whether this behavior is a matter of medical concern or not. Indicators to watch out for include: ^[1]

• Itching is persistent
• Scratching is severe enough to break the skin or cause hair loss
• Horse cannot be distracted from itching
• Itching is otherwise having a negative impact on quality of life

Depending on the cause, pruritis may be localized to a specific body area or generalized. ^[1]

Other signs of itchiness in horses include: ^[1]

• Biting
• Licking skin
• Rubbing against objects such as trees or fences

Concurrent Symptoms

If the itching is pathological (associated with a medical condition), it is often accompanied by additional symptoms. Depending on the underlying cause, horses with pruritus can develop the following: ^[2]

• Alopecia (hair loss)
• Skin crust
• Unpleasant odor
• Rash
• Scaling
• Fluid discharge
• Pustules
• Hives
• Red skin

Causes

Pruritus is generally triggered either by something on the skin that causes an urge to scratch it off or by an internal issue related to an underlying medical condition.

Causes of itching in horses include: ^[1][2]

• External parasites
• Insect bites/insect bite hypersensitivity
• Food allergies
• Airborne allergies
• Infections

In addition, pruritis may be one aspect of a multifactorial condition, such as scratches or photosensitization.

Ectoparasites

Horses are constantly exposed to the various species of insects and arachnids that populate their environment. Any pest species that bites mammals can potentially bite horses, leading to pruritus.

Horses may house several different external parasites (ectoparasites) that can cause persistent pruritus. Without medical intervention, the itching may worsen over time as these parasites continue to irritate the skin.

Lice

Phthiraptera, commonly referred to as lice, are small, flightless, parasitic insects that live on the skin of warm-bodied animals, including horses and humans. ^[3]

Lice are divided into two separate groups: ^[3]

• Chewing lice that feed on skin and hair
• Sucking lice that feed on blood and other body secretions

Almost 5,000 species of lice can be found worldwide. Many species have a specific host and prefer certain areas of the body to infest. ^[3]

Two species of lice can infest horses: ^[3][4]

• The horse biting louse (Damalinia equi) lives and lays eggs on the finer hairs of the horse’s body, located on the sides of the neck, the flank, and at the base of the tail.
• The horse bloodsucking louse (Haematopinus asini) can be found on the hair above the hoof, on the roots of the forelock and mane, and around the base of the tail.

Equine Lice Infestation

Female lice lay eggs (nits) and cement them to the host’s hair shafts near the skin. The eggs are oval-shaped, pale, and translucent in color. Once the eggs hatch, they feed on skin or blood and can continue reproducing without human intervention, potentially developing into a widespread infestation. ^[3][4]

Lice are passed from horse to horse via direct contact between animals. It is also possible to transmit lice through contact with infested objects (i.e. grooming equipment), but this is rare. ^[3][4]

Both species of lice cause itching in horses. Affected equines attempt to alleviate the pruritus by biting and rubbing, which may lead to skin lesions or hair loss.

The most effective method for eradicating lice is administration of topical, lice-specific insecticides. These products are only effective against larvae and adult lice, which means the eggs tend to survive treatment. As such, it’s necessary to repeat treatments at least two times at ten-day intervals or recurrence is highly likely. ^[3][4]

It’s crucial to treat all horses in contact with an affected animal for the treatment to be effective. If you’re unsure whether your horses have lice or if the treatments are working, consult your veterinarian for guidance.

Mites

Mites are very small arachnids, usually less than 0.4 inches long, that infest the skin of mammals. Skin mites in animals are collectively referred to as “mange,” and are most commonly associated with hair loss.

In horses, four specific species of mites are commonly associated with mange: ^[4]

• Sarcoptes scabiei: the common mite, also referred to as “scabies,” can cause an allergic reaction in horses that can lead to skin sores. This kind of mite creates burrows in the horse’s skin where the females lay their eggs.
• Chorioptes equi: the itchy leg mite feeds on the horse’s skin and fat. Infestation of itchy leg mites can cause progressive lymphedema, a debilitating skin condition in which lymph fluid builds up in the lower legs, causing swelling, ulceration, and skin folds, and can lead to lameness and life-threatening secondary infections.
• Demodex equi: hair follicle mites are generally benign but can, on occasion, cause the formation of abscesses on the neck.
• Psoroptes equi: the feces of the scab mite, which feeds on horse skin, cause allergic reactions of the horse leading to scabbing and hair loss on the mane and tail.

Mite infestations do not pose a severe health concern but can impact a horse’s general well being. Excessive scratching due to mange can cause skin lesions susceptible to secondary infections. Prevention is focused on maintaining overall hygiene, regular grooming, and proper disposal of infected clipped hair.

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Infections

Internal infections can also lead to pruritis in horses. In some cases the skin itself is infected and causes irritation directly. In others, activation of the immune system leads to widespread, generalized pruritus.

Regardless of the underlying cause, horses showing signs of infection benefit from timely veterinary assessment.

Pythiosis

Equine pythiosis, commonly referred to as swamp cancer or Gulf Coast fungus, is a severe and potentially life-threatening skin infection caused by the aquatic single-celled organism Pythium insidiosum. ^[5][6]

Pythium insidiosum is a plant parasite that commonly lives on aquatic vegetation. Horses become infected when spores of the organism come into contact with open wounds or abrasions. ^[5][6]

Affected horses develop severe ulcerative lesions on the limbs, abdomen, and occasionally on the face or neck. Horses infected by Pythium insidiosum suffer from extreme itchiness in some areas, which cause severe discomfort. ^[5][6]

An initial diagnosis of pythiosis is based on clinical presentation and physical examination; definitive diagnosis requires: ^[5][6]

• Tissue biopsy
• Culture of tissue samples
• Cytology

Treatment options are limited and non-definitive; they include: ^[2][5][6]

• Surgical removal of skin lesions
• Immunotherapy
• Antifungal medication; may be prescribed but has limited efficacy as Pythium insidiosum is not a true fungus
• Antibiotic therapy

The prognosis for equine pythiosis is poor and relapse is common. Left untreated, the condition has a 100% mortality rate. The best method to prevent infection is to limit horses’ exposure to stagnant water. ^[2][6]

Staphylococcal infections

Staphylococcal infections, or staph, are bacterial skin infections caused by a group of bacteria including: ^[7][8]

• S. aureus
• S. delphini
• S. epidermidis
• S. hyicus
• S. pseudintermedius

These bacteria are found in healthy equine microflora, but they can proliferate in the right conditions, producing an infection.

Clinical signs include: ^[8]

• Warm skin
• Painful skin
• Itching
• Circular crusts
• Lethargy
• Loss of appetite
• Fever

Treatment for Staphylococcus infections in horses is straightforward and consists of systemic antibiotic therapy and topical wound treatment. ^[2][8]

Pinworms

Equine pinworms (Oxyuris equi) are common intestinal parasites that infest the horse’s colon. These parasites do not cause direct damage to the horse’s system and are easily controlled with regular deworming.

However, affected horses develop severe itchy skin around the anus and tail that can lead to self-mutilation. Other symptoms may include: ^[9]

• Skin inflammation
• Lesions around the anus
• Hair loss
• Restlessness

Allergies

When the immune system overreacts to stimuli, it can lead to multiple allergic responses, including pruritis. Common forms of allergic reactions in horses include:

• Insect bite hypersensitivity
• Environmental allergies
• Food allergies

Insect Bite Hypersensitivity

Sweet Itch, also known as insect bite hypersensitivity, Queensland itch, or summer dermatitis, is a seasonal condition resulting from an allergic reaction to insect bites.

The condition causes severe itching, hair loss, and skin sores, leading to significant discomfort for affected horses. Sweet Itch is primarily triggered by an allergic reaction to the saliva of biting insects, particularly midges. ^[4]

Severely affected horses can become agitated and irritable. Treatment is focused on reducing discomfort and wound care for skin lesions to prevent secondary infections. ^[4][10]

Sweet itch is a chronic lifelong condition affecting around 10% of horses. As such, management and prevention are the best ways to minimize discomfort. Horses known to have insect bite hypersensitivity should be kept indoors during the evening when midge activity increases, especially from mid-May to September. ^[4][10]

Environmental Allergies

Horses live in environments that can contain high levels of common airborne allergens, such as mold spores, pollen, and dust. While most horses don’t react, some are hypersensitive to these allergens.

Pruritis is a common allergic response in domestic animals, including horses. Widespread itching and skin irritation associated with environmental allergies is referred to as atopic dermatitis or atopy. ^[11]

In some cases, atopy can escalate into a more pronounced, localized skin swelling called urticaria or hives. The severity of hives can vary depending on the horse and the allergen. In mild cases, the swellings may be small and disappear within a few hours without treatment. ^[12][13]

However, in more severe cases, hives can be widespread and cause significant discomfort and itchiness. Removal of the causative agent is a cornerstone in managing equine allergies. Veterinarians may prescribe antihistamines to manage the itching and swelling associated with hives. ^[12][13]

Food Allergies

Food allergies are an immune-mediated reaction to a certain type of food. While uncommon, horses can develop allergies to a number of grains and forages.

Identifying food allergens is a complex, long-term process requiring veterinary oversight. Once the specific allergen has been identified, it should be strictly avoided. Horses with food allergies are more likely to have other allergies, such as to insect bites and airborne allergens. ^[12]

Other Causes of Pruritus

Itching can sometimes be linked to internal processes beyond allergies and pests, highlighting the need for timely veterinary intervention. By accurately identifying the underlying cause of itching, owners and caretakers can make informed treatment and management decisions.

Photosensitization

Photosensitization, or photodermatitis, is a light-induced condition that causes the horse’s skin to become sensitive to sunlight. Photosensitization can be either primary or secondary.

Primary photodermatitis occurs following exposure to a phototoxic agent, usually in the form of plants or chemicals. These are compounds that cause the horse’s skin to inflame when exposed to UV light. Secondary or hepatogenous photosensitization is caused by an underlying liver condition. ^[14][15]

Symptoms of photosensitization in horse include: ^[15]

• Hair loss
• Skin edema (swelling)
• Itching
• Skin lesions
• Photophobia (squinting or avoidance of direct sunlight)
• Rubbing of ears, eyelids, and muzzle
• Redness
• Formation of pus blisters
• Scabs

Treatment of photosensitization depends on the underlying case. In cases of primary photosensitization, the first step in treatment involves removing the phototoxic source. In all cases, the horse should be sheltered from sunlight with minimal activity during recovery. Topical wound treatment may also be required. ^[14][15]

Scratches

Pastern dermatitis, commonly referred to as scratches, is a skin syndrome that causes inflammation of the horse’s lower limbs.

Scratches are not caused by a single factor but rather by a combination of factors including: ^[16][17]

• Dermal exposure to moisture
• Dermal trauma or injury
• Photosensitization
• Lowered immune system
• Compromised circulatory health
• Poor hygiene
• Bacterial infections
• Fungal infections

Symptoms of pastern dermatitis vary in severity and include: ^[16][17]

• Itchiness
• Discomfort
• Scaling skin
• Skin edema
• Lesions
• Hair loss
• Loss of appetite
• Lameness
• Thick, leathery skin
• Cracked skin

Initial diagnosis of pastern dermatitis is based on a thorough physical examination and medical history. Further diagnostic tools include:

• Bacterial or fungal culture
• Skin biopsy
• Skin scraping

Once diagnosed, treatment depends on the underlying cause. Affected horses may require antibiotic treatment, changes in environment or lifestyle, or topical medications. ^[16][17]

Diagnostics

If a medical cause of pruritis is suspected, diagnostics vary depending on the accompanying symptoms. Generally, initial veterinary investigation focuses on the skin and overall health status.

Diagnostic testing for itchy horses may include:

• Biopsies
• Skin scrapings
• Cytology
• Allergy skin stick testing
• Hair sampling
• Bloodwork
• Tissue culture

Management and Prevention

Effective management of pruritus involves identifying and addressing the underlying causes or conditions. Due to the wide range of conditions that can cause itching, prevention requires a multifaceted approach that takes into consideration environmental, nutritional, and health factors, including:

• Regular grooming
• Regular veterinary checkups
• Parasite control
• Environmental management
• Dietary management
• General hygiene

Many forms of pruritis in horses can be prevented or mitigated with strategic management choices to limit exposure to the triggering factor. For example, if your horse has confirmed insect bite hypersensitivity, it may be effective to stable them in the evenings when midge activity is highest.

Other mitigating strategies depend on the specific case, but may include:

• Use of fly sheets or masks
• Use of topical insecticides/insect repellants
• Dietary modifications
• Barn/stable air quality management
• Monitoring environmental heat and air quality before exercising

Feeding a balanced diet is an important part of supporting your horse’s skin health. Nutrients like zinc, copper, selenium, and vitamin E play important roles in maintaining the function and integrity of the skin and other components of the immune system, and also provide antioxidant support. ^[18]

Supportive supplements can also be helpful for horses with ongoing skin problems that are difficult to resolve. Supportive supplements often aim to provide anti-inflammatory or antioxidant support.

Omega-3 fatty acid supplementation can be helpful for horses with ongoing skin issues, because they can moderate inflammatory responses. For example, supplementing flax oil, a rich source of the omega-3 fatty acid alpha-linoleic acid (ALA), has been shown to reduce skin lesions and inflammation in horses with Sweet Itch. ^[19]

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In horses, spirulina supplementation may help inhibit histamine release and reduce pro-inflammatory antibody production. ^[21] Together, these properties may help to reduce the magnitude of allergic overreaction and ease itchiness in horses with some forms of pruritis.

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Summary

Horses show signs of itchiness by biting, licking, or rubbing their skin against objects to alleviate the scratching sensation.

• While often not severe, itchiness or pruritus can sometimes indicate serious conditions like equine pythiosis.
• Common causes of pruritus include insect bites, parasite infestations, bacterial and fungal infections, and allergic reactions.
• Regular grooming, maintaining hygiene, and managing exposure to known allergens and parasites can help prevent and control pruritus.
• Horses with itchy skin benefit from nutritional supplementation with omega-3 fatty acids and spirulina.