Patchy fur and itchy red skin often are the first and most obvious clues that a dog or cat has an allergy. Unfortunately, those clues frequently are misinterpreted, mistreated or ignored, leaving the pet to suffer unnecessarily. Here’s when to suspect that your pet has an allergy and what you can do about it…

Food Allergy

Dog signs: The skin of both of the dog’s ears and its rear end are itchy and/or red. The dog’s rear-end discomfort might result in frequent “scooting” across lawns or carpets.

Cat signs: Excessive scratching that leads to red and/or balding areas, especially on the head and/or neck. A food allergy also might make a cat vomit and/or overgroom, though this is only one of many potential explanations for these symptoms. In fact, vomiting and frequent grooming are so common in cats that they often are thought to be “normal.” However, there usually is an underlying reason for this, and often it is allergies. Rule of thumb: There’s cause for concern if the cat vomits several times or more per week…or when grooming becomes so common that patches of the cat’s fur are rendered short and stubbly.

What to do: If a food or treat was introduced to the pet’s diet within 72 hours of the onset of symptoms, stop providing this and see if the symptoms clear. If that is the cause, you should see improvement in five to seven days.

If the food is not the cause, take the pet to a vet to confirm that a food allergy is to blame and that there isn’t a secondary infection in the ears and rear. Also discuss diet modifications. Options might include a “novel diet”—with limited ingredients and a new protein, such as bison, venison, pork or rabbit, not commonly found in commercial pet foods…or a “hydrolyzed diet,” which breaks the proteins down enough that the dog or cat’s body doesn’t recognize them or attack them causing the allergic response.

Misinformation alert: You might have heard that the best way to solve a dog’s food allergy is to feed it a grain-free diet. In truth, grains such as corn are not common causes of food allergies among dogs. And when given to the animal long term, grain-free diets are associated with heart failure in many dogs.

Flea Allergy Dermatitis (FAD)

Dog and cat signs: Extreme itchiness and discomfort—the pet is so distressed that it can’t eat or nap without scratching. Areas of thinning fur and inflamed, red, scabby skin develop, especially around the base of the tail or elsewhere near the pet’s hindquarters, rear legs or belly. Among cats, overgrooming is a common symptom as well…and the areas of thinning fur and red skin also might appear on the head and neck.

A flea allergy could be the problem even if you don’t see any fleas on the pet. When a dog or cat is allergic to flea saliva, even a single flea bite days earlier can cause discomfort.

What to do: A vet can prescribe drugs such as corticosteroids to relieve the animal’s severe discomfort. Flea-preventive medications and lawn treatments can reduce the odds of future flea bites.

Best: Use pet-friendly flea treatments to treat carpeting, flooring, bedding and lawns. They all are different so follow instructions on the product label.

Related: If a pet is scratching at a single spot because of what appears to be a single bug bite, an ongoing allergy likely isn’t to blame. Apply a light layer of 1% hydrocortisone cream two or three times daily to this spot to ease the itchiness. If the pet can lick the spot, apply Aquaphor instead—it’s less likely to cause digestive distress or other issues when small amounts are ingested.

Environmental Allergy

Dog signs: The inside and flap of one ear—not both ears—is red and itchy. The animal’s eyelids also might be swollen and red.

Cat signs: Itchy, flaking skin on the head and face or potentially elsewhere. Scratching or overgrooming might lead to hair loss, stubbly hair patches and/or hairballs. Other potential symptoms among cats include watery eyes, runny nose, sneezing, respiratory congestion, vomiting and/or ear infections.

What to do: Reducing exposure to the allergen could lessen the symptoms—keep the pet indoors as much as possible if pollen or other outdoor allergies are suspected based on seasonality…and clean the house thoroughly if dust-mite allergies are a possibility. Routine weekly bathing can remove allergens from the pet’s skin and fur. A vet can prescribe medications to reduce the pet’s allergy symptoms including itchiness.

Misinformation alert: It used to be common to give pets suffering from environmental allergies over-the-­counter antihistamines primarily intended for humans, such as Benadryl. Recent research suggests that these provide little or no benefit for pets—they appear only to offer relief because they make pets so sleepy that they temporarily scratch less.

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