Q. Around this time of year, my pony starts getting very itchy. I know humans often take an antihistamine for itchiness, especially in the spring. Is it safe to give my mare an antihistamine for her itchiness? What else can I do to help relieve her itching?

If your pony’s itchiness (pruritus) occurs only during the warm time of the year, this could suggest an allergy to pollen (atopic dermatitis), fly salivary proteins (insect bite hypersensitivity), or biting insects. While antihistamines, such as hydroxyzine pamoate or cetirizine, can cause drowsiness in people, veterinarians rarely observe this adverse effect (or others) in horses. However, despite the relative safety of these drugs, antihistamines won’t be effective in treating all potential causes of equine seasonal pruritus, and the definitive treatment of your horse’s itchiness depends on the underlying cause. For example, while antihistamines can be quite effective for treating horses with atopic dermatitis (environmental allergies), insect bite hypersensitivity often warrants steroid treatment in addition to management techniques aimed at reducing exposure to biting insects.  

In addition, severe itchiness and the resulting trauma to the hair and skin caused by rubbing, rolling, and biting, can also cause secondary problems, such as hair loss and skin damage (crusting, scaling, ulcerations) that might also become infected. Consult your veterinarian to find the cause of your pony’s itchiness so she receives the correct treatment. Your veterinarian will likely ask you for a detailed history, including potential variations in your pony’s clinical signs (i.e., did you see any skin lesions prior to the start of the itchiness), when you noticed the problem, the environment where your pony lives (e.g., indoor stall, pasture access, proximity to bodies of water such as a pond), her travel history, other animals (and people) showing signs of itchiness, and her diet. 

Following a thorough physical examination, your veterinarian will closely inspect your pony’s skin to look for areas of hair breakage or loss and other skin lesions, such as a rash or crusting, and, if present, assess the distribution of these lesions. The location of lesions might provide helpful insights into what might be causing the itchiness. For example, skin lesions along the ventral midline (belly) are often associated with insect bite hypersensitivity, while facial itchiness and/or tail rubbing might be due to environmental allergies. Additional tests that might be warranted following this examination include skin scraping for cytology and bacterial culture, along with skin biopsy, allergy testing, and tests for ectoparasites.  

Once your veterinarian has established a diagnosis, treatment methods could include steroids, antihistamines, allergy shots (hyposensitization), and potential topical treatment of the affected areas. In addition, if biting insects are causing the itchiness, your veterinarian might also suggest management techniques such as stabling your pony during peak insect feeding times (sunrise and sunset), applying an insect repellent, using fans in stalls, attaching insect screens to barn windows, and using a fly sheet on your pony. For horses and ponies with fly bite hypersensitivity and environmental allergies, adding an essential fatty acid product (omega-3 fatty acids) to their diet might also help reduce the itchiness. 

Take-Home Message 

Working with your vet to determine what is causing your ponies itchiness is the best way to develop an effective treatment plan. While antihistamines might be effective for treating some allergies in horses, they are not effective for all, so your veterinarian will perform a physical examination and testing to decide which medication will be most effective for your pony. Combining medication with management changes can help reduce your pony’s itchiness and reaction to environmental allergies.