Equine Heat Rash: What Is It, and How Should You Treat It?

A man caring for his horse.

Over the last few years, we have been experiencing record-high temperatures during the summer. If you're a horse owner you may be attributing these high summer temperatures to your horse's heat rash condition each summer. The truth of this matter may surprise you. You see what we commonly mistake as heat rash in horses is actually a condition known as Urticaria, which is more commonly referred to as Nettle Rash or Hives. In this blog, you will learn what Urticaria is, how to identify it, and how to properly treat it as well as how to reduce the chances of your horse getting it.

What is Urticaria?

Urticaria is an allergic reaction experienced by horses that causes soft bumps and skin nodes to appear on a horse's skin. It often looks like multiple swollen bumps. Urticaria appears most often during the summer and spring months. This is because of the horse's reaction to an antigen or substance the horse's body deems toxic. This substance is often inhaled, ingested, or naturally applied to the horse's skin while it is out and about in the field. Heat doesn't actually play much of a factor in horses getting this condition. It just so happens that the condition is most common during the summer and spring months and that's why many people assume it is some form of heat rash. While heat related Urticaria is a thing, it is very rare. The most likely cause for your horse's Urticaria is a horsefly attack.

A quick side note on horse flies for those of you who are unaware. A horsefly is a rather large fly, they are generally a lot larger than your average housefly. Male horseflies are generally pretty harmless if not a bit annoying. It is the female horsefly that you need to be wary of. Female horseflies will drink the blood of larger mammals during their mating season. They do this to provide them with the nutrition needed for creating healthy eggs for their mating season. And what do you know? The horsefly mating season just so happens to be in the summer, around the same time horses tend to suffer from Urticaria. 

A horse with Urticaria.

Here is a visual example of what Urticaria can look like. Image courtesy of Kyeac.org.

How Do You Identify Urticaria?

So, we now know what Urticaria is, but we still need to be able to distinguish it from other skin conditions your horse may be suffering from. Urticaria’s lumps are usually the size coin, examples being a 25-cent coin or even a £1 coin. These lumps can be larger, smaller, or even fused together so keep an eye out! The lumps can also be recognized by the clear liquid that may ooze from them on occasion.

If your anti-horse fly measures are holding up then it may be something else that is causing your horse to get Urticaria. Reviewing any and all things that you have applied to your horse’s skin over the last few days may help you determine if your horse’s Urticaria is the cause of an allergic reaction to something you’ve applied to its skin. A common example of this is an anti-fly gel which does in fact keep those troublesome horse flies away, but it may also be triggering an allergic reaction in your horse.

Another way you can determine if the bumps are the cause of Urticaria or something else is to identify where exactly the bumps are being found. Urticaria is most often found in areas over and around the neck and flanks but can appear sporadically throughout the rest of the horse’s body. If you find that the horse’s lumps are isolated to other areas around the horse’s body the cause may be associated with something your horse is rubbing up against or sleeping against that is causing irritation.

A pleasant image of a brown horse.

Things are a bit heavy so far, here is a pleasant image to take your mind off this condition. Image courtesy of Unsplash.

How Do You Treat Urticaria?

Ideally, you should call your local veterinarian and have them come take a look at your horse's condition. They may be able to better identify what is causing the Urticaria to flare up and that will allow you to handle the problem with haste. It is advised that you do not try any special treatment procedures while awaiting the vet’s examination. You don’t want any outside drugs or factors throwing off the vet’s examination. In most cases, Urticaria clears up in about a day or two. If your vet allows it, you can try soaking your horse in some cool water to relieve some of the discomfort he or she might be feeling.

A horse laying down in a grassy field.

Remember to keep an eye on where your horse is laying and rubbing up against. These locations could be the cause of your horse’s Urticaria! Image courtesy of Unsplash.

How Can You Prevent Urticaria?

One option you may consider if you want to prevent your horse from suffering from Urticaria would be to ask your vet about allergy shots. Allergen-specific immunotherapy can be performed after an intradermal skin test. This test is used to figure out suspected allergens for your horse. It is similar to what we humans do for our allergy tests.

Antihistamines work well as preventions for Urticaria but are not advised for treating already existing cases of Urticaria. You should be careful when using Antihistamines since you may need to use many different kinds before you find one that treats your horse successfully. If your horse competes, the use of Antihistamines may or may not be allowed in the competition your horse is a part of. 


Urticaria really isn’t that scary. It is fairly common and doesn’t last that long either. The best way to treat Urticaria is to call your vet and have him or her take a look. This may seem like it's not necessary considering how little danger Urticaria typically causes for horses but we can't stress enough how much you should follow this advice. On rare occasions your horse could be experiencing a more dangerous allergic reaction or even an infection like skin parasites or ringworm, in these cases identifying them early with the help of your vet can save your horse a lot of pain and maybe even its life.

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