Hives in Horses

If you’ve been around horses long enough, sooner or later you will likely notice a horse that has developed raised bumps along their skin called horse hives, indicating they may be sensitive to something in their environment.

Hives in horses are a very common skin condition, and determining the cause of the hives will help you find the right treatment to clear it up.

What Are Hives in Horses?

Hives, also known as urticaria, are raised bumps or swellings on the skin, generally round in shape. They can vary in number, size, and severity.

The most common causes of hives in horses are allergies from insect bites or stings, reactions to a medication, or environmental allergens such as pollen.

Any horse can develop hives at any point in their life, but horses with more white coloring may be more prone to hives because they are more sensitive to allergies. Hives in horses can also occur due to sensitivity to insect bites.

Severe cases of horse hives can lead to trouble breathing and even anaphylaxis, which is a life-threatening allergic reaction.

In some cases, hives on horses are a mild one-time event and they go away quickly on their own. In these cases, you may not need to determine the cause. However, for hives that don’t resolve on their own, or come back multiple times (chronic hives), you should work with your vet to determine possible causes and management/treatment plan.

Any time you notice hives on your horse, call your equine veterinarian for their recommended treatment. Hives in horses are considered a medical emergency if they appear to be getting worse or your horse is breathing abnormally.

Symptoms of Hives in Horses

Hives in horses are characterized by the following clinical signs:

• Raised round swellings on the skin (0.5 inches to 8 inches in diameter)

• Itchiness

In severe cases you may also see the following symptoms:

• Fever

• Poor appetite

• Restlessness

• Dull coat

• Agitation

While horse hives can develop on any part of the body, most commonly they occur on a horse’s:

• Back

• Flank

• Neck

• Eyelids

• Legs

In advanced cases, hives may also develop on the mucus membranes of the mouth, nose, or eyes, as well as on the rectum or vagina (this is uncommon). 

Causes of Hives in Horses

Some of the most common causes of hives in horses are due to:

• Insect bites or stings

• Medication sensitivity

• Exposure to environmental allergens (commonly pollen)

Some less common causes of hives include:

• Vasculitis (inflammation of blood vessels)

• Food allergies

• Ringworm

• Pemphigus foliaceus (a rare autoimmune disease that causes sores on the skin)

Atopy, a type of allergic reaction that affects the skin or respiratory system, can lead to hives and be an inherited condition. Some horse breeds, such as Thoroughbreds and Arabians, may have more skin sensitivities.

How Veterinarians Diagnose Hives in Horses

Generally, your veterinarian will be able to diagnose hives based on a physical exam. If a horse has chronic hives, your veterinarian may recommend further diagnostic testing to help determine the root cause.

Types of Diagnostic Testing for Hives in Horses

Elimination Testing

Elimination testing involves removing items from your horse’s routine that may trigger hives. Products to consider removing may include:

• Non-essential supplements

• Shampoos or conditioners

• Fly spray or ointment

See if your horse’s skin recovers from the hives after removing these items, and then gradually introduce them back to your horse’s routine one at a time. If your horse’s skin reacts to a specific product on reintroduction, you’ve found the likely culprit!

Allergy Testing

Elimination testing cannot always pinpoint the exact origin of your horse’s hives. In this case, allergy testing may be recommended. There are two types of allergy testing for horses:

1. Intradermal testing, where a small amount of certain allergens is injected into the horse’s skin to see if there’s a reaction

2. Blood testing, where serum of the horse’s blood is analyzed to check for the presence of antibodies against certain allergens

Blood testing is less invasive than intradermal testing, but is considered less accurate.

Since hives can be extremely uncomfortable for a horse, it’s important to work with your vet to determine the underlying cause, especially if they have reoccurring episodes.

Horse Hives Treatment

Treatment for hives in horses typically consists of non-steroidal anti-inflammatory medications such as Banamine®, steroids such as dexamethasone, or antihistamines.

Medicated shampoos may also be helpful for horses with skin issues, particularly for horses that experience hives.

Recovery and Management of Hives in Horses

Horses typically recover from hives within a few hours with no complications. If hives or skin conditions become a chronic concern, an Omega-3 fatty acid and MSM supplement may be recommended.

For horses that are extra sensitive to bug bites that trigger hives, you’ll want to invest in a good fly spray as well as other protective measures including a fly sheet, fly mask, and boots. Reducing bug bites can help to prevent hives from occurring.