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What are Allergic Dermatitis?

Conditions such as a contact allergy, an adverse reaction to a fly bite or a developed sensitivity to the sun can all contribute to allergic dermatitis in your horse. While some cases may be seasonal (such as sweet itch), others are due to genetic predisposition. Studies show that Arabian and Thoroughbred horses may be prone to atopic dermatitis and urticaria is a skin condition more common in horses in general than in other animals. A food sensitivity or a an aversion to fly bites are two other causes for itchy skin in horses.

Allergic dermatitis in horses is a skin condition that results in your horse’s skin becoming itchy and is also known as pruritus. The itching can be the result of multiple factors such as insect bites and reactions to the sun or chemicals.

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Symptoms of Allergic Dermatitis in Horses

  • Itching
  • Self mutilation
  • Biting at his side
  • Crusting of bites or sunburn
  • Sores that scab over 
  • Loss of hair
  • Changes to coat 
  • Dandruff
  • Redness, inflammation, and scaling of his skin
  • Infections, these are often secondary to sores that are opened by the continuous scratching 

Types

Skin reaction in the form of allergic dermatitis may be due to:

  • Food allergy
  • Insect bite
  • Reaction to the sun
  • Inhalant allergy (pollens for example)
  • Urticaria

Causes of Allergic Dermatitis in Horses

  • Sand-fly – When your horse has a severe reaction and hypersensitivity to this insect’s bite, he can develop an allergic reaction; this becomes a bigger problem during the summer months when the flies are more prevalent
  • Black flies – These insects tend to seek out the head and ears of horses as their hosts; the allergic reaction can be caused by the anticoagulants that the black flies inject into the bite site
  • Allergens – There are some cases in which your horse may develop an allergy to inhaled allergens such as mold, pollen and dust
  • Food – Your horse may develop a hypersensitivity to the food he is consuming as well (grass, grains, additives in his food or supplements you are feeding him)
  • Chemicals – The allergic reaction may be caused by your horse’s contact with shampoo, soap or other interaction with chemicals
  • Sun – There is evidence that horses do develop sensitivity to light and the sun
  • Plants -- This condition may activate once certain plants are consumed causing sores on the skin

Diagnosis of Allergic Dermatitis in Horses

The determination of the cause of allergic dermatitis will involve much evaluation. The veterinarian may ask:

  • Is the pruritis  or urticaria seasonal?
  • What other clinical signs are evident?
  • Are the hives or itchiness constant or recurring?
  • Is there secondary infection?
  • Where is the skin reaction located on the body and is it localised?

Tests that may be done, depending on the suspected reason for the allergic dermatitis, are intradermal allergy tests, blood tests, skin scraping, biopsy, or food elimination test.

Treatment of Allergic Dermatitis in Horses

Treatment for allergies falls into 3 categories which are medication, elimination and prevention. Depending on the cause of your horse’s allergies, these can be used alone or in conjunction with one another. Certain medications have been found to be more effective than others, along with necessary changes to lifestyle and diet. 

Medication

The first line of medication management for the symptoms of allergies in your horse will be corticosteroids. This is an anti-inflammatory drug that will help with his itching, allowing him to heal. There is some evidence that using antihistamines will help to reduce his symptoms as well. Fatty acids are often prescribed as well to help with symptoms. 

In the category of medications, shampoos and topical applications are also utilised. This can include oatmeal shampoos to help with the inflammation of his skin. Corticosteroids can also be prescribed as topical ointments. 

Elimination

If food reactions are suspected, elimination of all food down to a basic diet of hay and water may be suggested. The diet must be maintained for 4 weeks. Slowly reintroduce  items, one by one, back into the diet.

The same holds true for chemicals such as shampoo or insect repellants. Stop using them all if possible; slowly use them again on your horse to see how he reacts with only one at a time. Once you find the item he is allergic to, eliminate it in his diet or from his maintenance routine from that point forward. 

Prevention

When it comes to insects, prevention will help greatly in reducing your horse’s discomfort and risk of allergic reaction. For insects that are more prevalent in the summer/warm months, keeping him stabled during the day will help prevent his exposure to them while using a fan to help insects to not land on your horse. Providing a protective mesh lining to your horse’s stall can be beneficial as can providing him protection for his face and body when he is out. 

Spraying the area your horse will frequent for insects can reduce the overall amount close to him and provide him with fewer odds of being bitten. You can also spray your horse directly with insect repellant; always check with your veterinarian first for recommendations. 

Lastly, keep the area clear of insect breeding grounds (no standing water, no trash, clean up area). This will deter the insects from coming to your area and biting your horse.

Recovery of Allergic Dermatitis in Horses

Follow up will only be needed in the event your horse does not respond to the treatment options provided. Your veterinarian will discuss this as needed. Ensuring that your horse is not in an environment that welcomes or invites insects to him will be necessary. 

If the issues are due to food, inhalation of pollens or a chemical reaction, identifying and eliminating the irritant or allergen from his diet/routine will be a necessary part of the lifestyle change. Finding the cause of an allergy can take up to 4 weeks (elimination diet) and then treatment begins from there. Assuming the allergen is identified and taken out of the horse’s life, recovery should be relatively quick. However, if there are any secondary infections or open sores, these may take longer to heal.