Suddenly, thick welts appear all over your horse's body – as if it had been lying in nettles. Hives (medically known as urticaria) are a common allergic reaction in horses, which can range from harmless to life-threatening. In this guide, you will learn how to recognize hives, when it becomes an emergency, what triggers it, and how you can help your horse both in the short term and long term.

What is hives and how does it develop?

Horse hives is an acute skin reaction in which raised, localized swellings (wheals) form on the skin within a very short time. These are caused by an excessive reaction of the immune system, in which histamine and other messenger substances are released. The blood vessels become more permeable, fluid leaks into the tissue, and the typical wheals form.

What does hives look like in horses?

Small to large, raised swellings on the skin. The wheals are clearly defined and feel firm to the touch. They can range in size from a few millimeters to several centimeters. The skin over the wheals is often tight. The swellings can occur individually or merge to form larger areas. Typically, the wheals develop very quickly—often within minutes to a few hours.

Where do the hives appear?

In principle, hives can occur anywhere on the body. 

Causes: What triggers hives?

There are many triggers for urticaria in horses. Finding the cause is often like detective work:

1. Feed allergies:

New feed or sudden change in diet. Certain types of grain, protein sources, or additives. Moldy or spoiled feed. Treats with artificial additives or preservatives.

2. Insect bites:

Mosquitoes, horseflies, or other biting insects. Particularly common in summer and in pastures. For some horses, even a single bite is enough.

3. Medications:

Antibiotics, especially penicillin. Anti-inflammatory drugs. Vaccinations (as a rare side effect). Deworming agents.

4. Contact allergies:

Detergent residue in blankets or bandages. Cleaning agents or disinfectants. New saddle pads or girths. Fly sprays or care products.

5. Environmental allergens:

Pollen from trees, grasses, or herbs. Mold spores in hay or straw. Barn dust.

6. Stress and physical exertion:

Intensive training can trigger hives in some horses. Stress or excitement can also be a trigger.

7. Infections:

Sometimes hives occur in connection with viral or bacterial infections. The body reacts to the pathogens or their breakdown products.

Have you noticed hives on your horse and are unsure of the cause? The specialists at Altano clinics can help with diagnosis. Find a clinic near you now.

Harmless hives or dangerous emergency?

Most cases of hives in horses are unpleasant but not dangerous. However, there are situations in which you must act immediately:

Harmless – observation sufficient:

Single or multiple welts on the neck, shoulder, or body. The horse shows no signs of illness and eats normally. Breathing is normal, no coughing. No swelling in the head area. The welts may itch slightly, but the horse is not panicking.

Observe carefully – contact your veterinarian:

Many welts all over the body. The welts spread quickly. The horse appears restless or shows signs of discomfort. Slight swelling in the head area (nostrils, eye area). The welts last longer than 24 hours.

Emergency – call the veterinarian immediately:

Swelling in the head area, especially around the nostrils, mouth, or larynx. Shortness of breath, wheezing, or rapid breathing. The horse shows signs of panic or severe restlessness. The mucous membranes are bluish in color (lack of oxygen). Additional circulatory problems – increased pulse, weakness, staggering. Swelling that spreads rapidly within minutes.

Caution: Swelling in the head and neck area can lead to anaphylactic shock or respiratory distress due to swelling of the airways. This is life-threatening!

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First aid for hives

If you discover hives on your horse, you can help with these immediate measures:

For harmless wheals:

Take the horse to a quiet, shaded area. Remove any possible triggers: take off blankets and put away any feed that has been newly introduced. Carefully cool the affected areas with cold water – this will relieve itching and reduce swelling. Observe the horse closely – take photos of the welts to document their progress. Initially, only give your horse hay and water—do not give it any other feed until the cause has been determined.

In case of emergency symptoms (until the veterinarian arrives):

Remain calm—your calmness will transfer to the horse. Keep the airways clear—remove the halter and anything else that could constrict the neck. Walk the horse slowly if it remains calm—movement can promote blood circulation. Document the exact time of onset and all activities/feed consumed in the last few hours.

What you should not do:

Do not administer any medication without veterinary advice—not even supposedly harmless painkillers. Do not apply any ointments or creams to the welts. Do not rub or massage the swollen areas. Do not leave the horse alone, especially if it is showing emergency symptoms.

Veterinary treatment

Your veterinarian will first assess the severity of the reaction and then take appropriate action:

Acute treatment for hives:

Antihistamines: These block the effect of histamine, thereby reducing itching and swelling. They are usually given as an injection for fast relief.

Corticosteroids: Anti-inflammatory cortisone preparations are used for more severe reactions. These act quickly and effectively against the allergic reaction.

Infusions: For circulatory problems or to support kidney function in eliminating allergens.

Long-term treatment for chronic hives:

If hives occur repeatedly, a systematic search for the cause is necessary:

Elimination diet over several weeks to identify feed allergies. Allergy tests (blood test or intradermal test) to identify environmental allergens. Keeping a diary: When do the hives appear? What has the horse eaten? What activities took place? Long-term administration of antihistamines during the allergy season. In severe cases: immunotherapy (desensitization).

Does your horse suffer from repeated outbreaks of hives? The experts at the Altano Group can help you identify the cause and provide long-term treatment. Get in touch now.

Root cause analysis: How to find the trigger

In cases of one-time hives, it is often difficult to identify the cause. In cases of recurring hives, you should proceed systematically:

1. Keep an allergy diary:

Make daily notes: What did the horse eat (including treats)? What activities did it do (training, riding, grazing)? What products were used (grooming products, fly spray)? When did the hives appear? What did they look like? Weather conditions and pollen count.

2. Follow an elimination diet:

Feed only hay and water for 4 to 6 weeks (after consulting your veterinarian). When the symptoms disappear, slowly reintroduce individual feedstuffs – at intervals of 5 to 7 days. If the hives reappear, you have found the culprit.

3. Test for contact allergens:

Wash all blankets, bandages, and saddle pads with hypoallergenic detergent. Try out different care products one after the other. Observe whether any changes occur.

4. Consider seasonal patterns:

Does hives only occur in spring/summer? → Suspected pollen allergy or insect bites. Only in winter? → More likely a feed or mold allergy caused by hay. After certain activities (e.g., always after training)? → Exercise-induced urticaria.

5. Have allergy tests done:

Blood tests (IgE determination) can provide indications of allergies. Intracutaneous tests (small amounts of various allergens are injected into the skin) show direct reactions. These tests are not 100 percent reliable, but they do provide important information.

Do you need help with allergy diagnosis? Altano Clinics offer comprehensive allergy testing. Make an appointment. 

Management of chronic urticaria

If your horse regularly suffers from hives, you can help with these measures:

Feeding management:

Feed only high-quality, tested food. Avoid food with lots of additives. If allergies are known: strictly avoid triggers. If necessary, supplement with natural antihistamines such as black cumin oil (after consulting your veterinarian).

Posture optimization:

Reduce dust in the stable by moistening the bedding or using dust-free material. Ensure good ventilation without drafts. For pollen allergies: Keep the horse in the stable during the main pollen season (usually in the morning). Put the horse outside at night when the pollen count is lower.

Insect protection:

Fly masks and eczema blankets protect against insect bites. Use compatible insect sprays. Avoid grazing near standing water (breeding grounds for mosquitoes).

Stress reduction:

Keep the daily routine as consistent as possible. Avoid unnecessary stress (frequent herd changes, long transports). Ensure sufficient exercise and mental stimulation.

Medication prophylaxis:

During allergy season, preventive administration of antihistamines may be beneficial. Talk to your veterinarian about an individual treatment plan.

Special situations: Hives after vaccinations

Occasionally, hives occur as a side effect after vaccinations. This is usually harmless, but should be noted:

Typical course:

Wheals develop 6 to 24 hours after vaccination. They are usually spread across the entire body. They are generally harmless and disappear on their own within 24 to 48 hours.

What you should do:

Keep a close eye on the horse. Inform your veterinarian—they can decide whether treatment is necessary. Document the reaction for future vaccinations. 

When things get serious:

If you also experience shortness of breath, circulatory problems, or severe swelling in the head area, this is anaphylactic shock—a medical emergency!

In rare cases, wheals may also occur after physiotherapy treatments, especially after intensive measures such as fascia release. These skin reactions are usually temporary and subside on their own within a short period of time.

Would you like to learn more about vaccine reactions and how to manage them? The veterinarians at the Altano Group will be happy to advise you. Make an appointment.

Forecast: What are the prospects?

The prognosis for hives depends on the cause and the possibility of avoiding the trigger:

Acute, one-time hives:

In most cases, the hives disappear completely within 24 to 48 hours. With treatment, significant improvement is often seen after just a few hours. No lasting damage is expected. If the trigger can be identified and avoided, the problem will not recur.

Chronic or recurrent urticaria:

The prognosis depends on whether the cause can be identified. If the trigger can be identified and consistently avoided: good prospects. If the cause is unclear or the allergens cannot be avoided: long-term management is necessary. However, modern treatment options enable patients to lead a largely normal life.

Emergency situations:

With timely treatment of anaphylactic shock, the prognosis is good. Affected horses should be closely monitored in future risk situations (vaccinations, known allergens).

Prevention: Can hives be prevented?

Not all cases can be prevented, but you can reduce the risk:

Introduce feed slowly – never make abrupt changes. Use high-quality feed without unnecessary additives. Keep the stable clean and free of dust. Protect your horse from insects during the appropriate season. If allergies are known: strictly avoid triggers. Strengthen the immune system through needs-based feeding and stress-free husbandry. Document all reactions – this will help you recognize patterns.

Conclusion: Take hives seriously, but don't panic.

Hives in horses are unpleasant in most cases, but not dangerous. Here is a summary of the most important points:

Recognize the symptoms—sudden hives on the body. Distinguish between harmless and dangerous situations—swelling in the head area is an emergency. Search systematically for the cause – an allergy diary can help. If hives recur, have a thorough allergy diagnosis carried out. With the right management, even horses with chronic hives can lead a normal life.

With attention, systematic investigation of the causes, and the right treatment, most horses can live well with hives.

For better readability, we predominantly use the generic masculine in our texts. It goes without saying that all personal designations refer equally to all genders. The abbreviated form of language is used solely to improve comprehensibility and is to be understood in an unbiased manner.