Scratching the Itch

Does it seem like your pets are more prone to skin problems than ever before? Veterinary research and pet insurance data show that allergies are now among the most diagnosed chronic conditions in animals.

Increased awareness, improved diagnostics, year-round allergen exposure, and modern approaches to how pets are housed are all potential contributors to this rise.

“Changes in living conditions and hygiene standards may reduce animals’ exposure to harmless organisms that play roles in training the immune system early in life,” said Dr. Tyler Jordan, assistant professor and board-certified veterinary dermatologist at the UC Davis Weill School of Veterinary Medicine. “Animals also live in more urban settings, with greater exposure to pollutants, irritants, and indoor allergens, and are increasingly fed more processed diets. The popularity of breeds genetically predisposed to allergies, like Golden Retrievers and French Bulldogs, may also be a factor.”

What are Allergies?

Allergies occur when the immune system overreacts to normally harmless substances called allergens. These include pollens from trees, grasses, and weeds, house dust mites, mold spores, insect bites, and dietary proteins. Allergen exposure triggers immune cells to release chemicals that lead to itching, redness and swelling, ear infections, and breathing or digestive issues.

Allergies can change over time, and many pets are allergic to more than one thing. In dogs and horses, allergies may have a genetic component. Importantly, itching and inflammation are not exclusive to allergies. Infections, parasites, and other conditions may have similar signs.

“Itching does not always equate to allergy, even though the terms are used interchangeably,” Jordan noted. “A lot of things can cause an animal to itch, including allergies and a variety of other causes.”

Licking, scratching, chewing, biting, rolling, rubbing, and shaking are normal behaviors, especially in cats and other fastidious groomers. However, if the behaviors become so frequent or intense that they impair an animal’s quality of life and normal activities, such as eating or sleeping, or result in hair loss, rash, or recurrent infection, it is time to visit your veterinarian.

Common Allergies in Pets

Insect allergies

Insect allergies are the most common cause of allergic skin disease in many species. Flea allergy dermatitis in dogs and cats is caused by proteins in flea saliva that are injected every time a flea bites the skin. Even a single bite can trigger severe itching and skin inflammation.

Additional signs include hair loss, scabs, inflamed or oozing skin, and secondary bacterial or yeast infections. Fleas are active year-round in California, including indoors, so consistent flea control measures are critical.

Insect bite hypersensitivity caused by biting midges (Culicoides) is the most common allergic skin disease in horses. It can lead to “sweet itch” (seasonal recurrent dermatitis) and intense itching of the mane, tail, belly, face, ears, and limbs. Breeds such as Icelandic Horses appear genetically predisposed.

Diagnosis relies on history, seasonality, distribution of skin lesions, and response to treatment. Skin testing may help identify specific insect allergens, but unaffected animals can have positive results, so it is not reliable for diagnosis. Treatment entails strict insect control, environmental management, and medications to provide short-term itch relief and treat infections.

Environmental allergies

Environmental allergies, or atopic dermatitis, occur when the immune system reacts to unavoidable allergens such as pollens (trees, grasses, weeds), mold spores, house dust, and storage mites. They are the second most common skin allergies.

Signs include chronic itching, recurrent ear and skin infections, and hair loss. Less commonly, pets (especially cats) can develop respiratory signs such as sneezing, watery eyes, or asthma-like symptoms.

In horses, environmental allergies can result in hives and itching, or affect the respiratory system, causing coughing and nasal discharge. Chronic exposure to barn dust can lead to recurrent airway obstruction, labored breathing, and poor performance.

Treatment involves reducing allergen exposure, anti-inflammatory medications, and de-sensitizing allergy shots or drops.

Contact allergies

Contact allergies are less common in pets than other allergies. They are caused by direct skin contact with an allergen, such as shampoos, cleaning products, bedding, plants, or topical medications. Diagnosis involves identifying and eliminating suspected triggers. Short-term medical management may control active signs.

Food allergies

Food allergies are relatively uncommon in pets. Although rare, they can occur in any species and involve any protein or carbohydrate. Signs include non-seasonal itching, skin and ear infections, hair loss, and gastrointestinal issues such as vomiting, diarrhea, burping, farting, stomach rumbling, scooting, and recurrent
anal gland issues.

“We diagnose food allergies in 20% or less of the dogs and cats that we see,” Jordan estimated. “Most also have environmental and flea sensitivities.”

Diagnosis requires an elimination diet trial lasting 8-12 weeks. Treatment involves long-term nutritional management, avoidance of the offending ingredients, and short-term management of itch and skin infections.

Allergy Testing: What It Can (and Can’t) Tell Us

The allergy tests most used by veterinary dermatologists are intradermal skin tests and blood tests for environmental allergies.

“One of the biggest misconceptions about allergy testing is that it can diagnose animals with environmental allergies,” Jordan shared. “The problem is that positive results are common even in unaffected animals. The only reason we perform allergy tests is to determine what allergens to include in an animal’s allergy vaccine.”

According to Jordan, environmental allergy testing should only be performed: 1) after a diagnosis of environmental allergies has been made based on clinical signs; and 2) when a pet owner is interested in de-sensitizing allergy shots or allergy drops.

While blood tests are available to screen animals for food allergies, these can also be hard to interpret and may not provide clinically meaningful information. Food allergies can only be confirmed through strict elimination diet trials using hypoallergenic prescription diets or home-cooked foods.

Treatment: Multimodal, Lifelong

Allergies cannot be cured but can be managed through approaches tailored to the individual animal and situation.

“It is important to continue maintenance treatments even when the pet seems comfortable and the skin looks normal,” Jordan emphasized. “These conditions require ongoing management, often for the life of the animal, to prevent flare-ups.”

Desensitization through immunotherapy, which involves individualized allergy vaccines in injections or oral drops, can gradually retrain the immune system. It is effective in approximately 70% of cases, especially when started early, but can take up to a year to see results.

Anti-inflammatory and anti-itch medications may be useful for managing active signs. Antihistamines can alleviate signs in some horses but are generally not effective in dogs and cats. Topical therapies, such as hypoallergenic or medicated shampoos and mousses help remove allergens and soothe inflamed skin. Antiseptic shampoos and mousses are often prescribed to treat secondary infections.

New medications are also becoming available that are similar to targeted medications in humans and could greatly expand treatment options for pets.