19/07/2025
Treatment and Control of Allergic Skin Disease
Brian S. Burks, DVM
Diplomate, ABVP
Board-Certified Equine Specialist
Elimination or reduction of allergen exposure is ideal, but often impractical for equine allergies. Most horses are treated with a combination of management changes, allergen immunotherapy, pharmacologic intervention, dietary supplementation, and medicated shampoos.
Horses should be stabled during peak feeding times of biting insects. Stable flies, horse flies and deer flies are daytime feeders and prefer bright sunlight. Black (Simulian) flies are most active in the morning and evening, Culiciodes feed from dusk to dawn and mosquitoes are most active from dusk to two hours past sunset. Stabling of horses with mist sprayers of pyrethrins may offer the best protection. Cypermethrin or permethrin (>2% concentration) in combination with piperonyl butoxide can be applied twice daily. Topical spot on products such as Vectra 3D are long acting and can be applied to the horse or to fly sheets. Other products may be 44-64% permethrin, marketed specifically for horses. Such products may cause hair loss, and application of vitamin E oil is advised to mitigate this effect. Insecticide impregnated fly sheets are also available, as have "body suits" of light weight fly sheets and fine mesh. The face and ears should be covered, along with the ventrum and limbs. Other products may contain picaridin, which lasts up to 12 hours and works very well.
Some insecticides may result in contact allergy, making the use of fans to prevent insect an attractive option. Screens may afford protection but must have 60 squares per square inch to exclude Culicoides. Mosquito magnets attract and kill mosquitos, black flies, Culicoides, sand flies, and other biting insects with carbon dioxide. Turn out near bodies of water, manure piles, and cattle should be avoided whenever possible. Any standing water should be removed and water troughs routinely cleaned or chlorinated. Finally, larvicidal feed supplements and fly predator wasps can be used to reduce insect populations.
Corticosteroid medications have been the mainstay of insect bite and allergic response treatments. For local reactions topical steroids work well, but for generalized pruritis, systemic therapy is required. As with all medications, steroids can have unwanted effects, including mood changes, increased susceptibility to infection, and, ostensibly, laminitis. The lowest effective dose, preferably every other day, should be used. A combination of the best avoidance control possible and oral every other day administration of prednisone or prednisolone often will provide adequate control. Pentoxifylline is a phosphodiesterase inhibitor that has immunomodulating effects and lessens the response to inflammatory cytokines. It also may minimize the laminitis risk with corticosteroid therapy.
Antihistamines and tri-cyclic antidepressants can be used to reduce the need for steroid use. Their effect is variable, and several different classes may need to be tried before finding an effective treatment. The histaminic response is not great in horses, making antihistamines unreliable, but potentially helpful.
Allergen Specific Immunotherapy, or hyposensitization, can be helpful in some cases. The cause of the allergy is identified by intradermal or serum testing. The former is the most reliable. The goal of ASIT is to redirect the immune response to an allergen, reducing the hypersensitivity reaction. Approximately 60-85% of horses respond to ASIT, although it may take as long as 24 months to see effects; most respond within 8 months. Unlike other therapies, ASIT can result in remission of the allergy. This therapy is recommended for insect bite hypersensitivity, recurrent urticaria, and atopy. Other therapies may be used concurrently.
BarItch is a new product to help skin. This scientifically formulated supplement is designed to relieve pruritus (itching) and related symptoms in dogs and horses. It uses a unique blend of natural ingredients, BarItch™ targets multiple biochemical and neurophysiological pathways to provide effective relief beyond traditional antihistamines. The product combines betulinic acid from birch bark extract, Alaska wild blueberry/bilberry concentrate, astaxanthin, resveratrol, and a concentrated extract of Alaska wild rosehips. Additional active ingredients—including Alaska wild yarrow concentrate, quercetin, luteolin, red clover extract, and carotenoid-rich carrot powder—offer anxiolytic and mood-enhancing benefits, further supporting overall well-being. This product has been beneficial to many equines with skin disease, shown by clinical testing.
Many horses with chronic insect hypersensitivities have a type IV (delayed) allergic response to insect bites as well as an immediate of type I response. Since delayed hypersensitivity is not immunoglobulin mediated, response to a hyposensitization regimen is less likely. It is important to remember that hyposensitization begun during the middle of the insect season and height of the allergic response is very unlikely to improve the horse during the current season.
Omega-3 fatty acids work synergistically with steroids and antihistamines to decrease inflammation. Fresh ground flax has anti-inflammatory properties in the skin of allergic horses. Whole flax seed passes through the equine digestive tract intact; however, ground flax becomes rancid within 7-10 days. A coffee grinder works well to make powder of the flax seed, which is then fed at 0.5-1 pound per day.
As many allergens are presented to the body enter transcutaneously. Topical therapy with appropriate shampoos removes allergens from the skin and rehydrates the skin, improving the epidermal barrier integrity. Horses should be bathed in cool water to restrict blood vessels, minimize histamine release, and delivery of other inflammatory mediators. Strong detergent shampoos should be avoided as they remove fats from the skin, which are important in the skin’s barrier protection. There are many moisturizing shampoos and colloidal oatmeal products, which must be left on for 15 minutes to cool and hydrate the skin, increasing the pruritic threshold. Horses with secondary skin infections require medicated shampoos with antibiotics and/or antifungal agents. Some horses need systemic antibiotic therapy.
In all cases of pruritic dermatitis, management to decrease exposure to allergenic agents, as well as symptomatic therapy to reduce pruritus is warranted. All avenues available to decrease exposure to insects should be fully implemented. Heat, humidity and solar radiation exacerbate pruritus, thus the provision of shade and wind currents by fans can provide relief. Simple feeds and whole grains are better than mixed multiple grain sweet feeds. A complete and detailed investigation into the etiology of the disease should occur concurrently with general symptomatic care. Hypersensitivities and atopy are lifelong disorders, necessitating continuous management and/or therapy. A horse may be symptom free with low exposure to inciting antigens and symptomatic as the antigen "load" increases. Antigen exposure is additive, thus comprehensive management is needed to best control clinical disease.
Fox Run Equine Center
www.foxrunequine.com
(724) 727-3481
