Allergic Skin Disease

By: Jessica Colborn, DVM

TVMA Member
Magnolia, TX

Published June 2014

It is important to understand that your veterinarian cannot cure your pet’s skin allergies, but they can be managed. When humans sneeze and get watery eyes, we take an antihistamineA drug or other compound that inhibits the physiological effects of histamine, used especially in the treatment of allergies. to ease our symptoms. When it is really bad, we may get a sinus infection, so we go to the doctor and are put on medication. For most people, this happens rarely, but some people get repeated sinus infections until their doctor finds the right combination of medications to manage their allergies. If they stop the medication, the sinus infection comes right back.

Instead of getting a sinus infection, dogs and cats tend to develop skin and ear infections secondary to allergies. Common allergies in dogs and cats include flea hypersensitivityUndesirable reactions produced by the normal immune system, including allergies and autoimmunity., food allergies and inhaled allergies (atopy). We try to distinguish between them based on seasonal occurrence and pattern of itching.

Flea Hypersensitivity

A flea hypersensitivityUndesirable reactions produced by the normal immune system, including allergies and autoimmunity. means that your pet has an abnormally strong reaction to flea saliva. Flea bites itch like a mosquito bite, but when a pet is hypersensitive to flea saliva, even one bite can cause a reaction so severe that a pet itches very badly all over its body. The affected area tends to center on the back between the ribcage and the tail. Sometimes we don’t see a single flea on these pets because they groom themselves so thoroughly that they swallow any flea that bites them immediately.

Controlling the fleas is the best way to control this allergy. This is easier said than done. It means strict flea control for every animal in the house and yard. This means cats, dogs, ferrets, rabbits and any other host animal needs topicalRelating or applied directly to a part of the body. or oral treatment monthly, if not every other week. If you have a lot of stray animals around your house, you may need to treat the yard regularly. You and your veterinarian may have to try a few different combinations of flea treatments to find what works best for your pet and your environment.

Food Allergies

Food allergies are a hypersensitivityUndesirable reactions produced by the normal immune system, including allergies and autoimmunity. to one of the ingredients in your pet’s food. Pets that are affected by food allergies will often have have itchy feet, ear infections and frequently itch around their anus. We control this allergy by feeding a hypoallergenicRelatively unlikely to cause an allergic reaction. food. Many clients say, “It can’t be his food; I switched foods, and he still itches.” Food allergies aren’t that easy to rule out. A real food trial means that you use a prescribed diet that has only very specific sources of protein and carbohydrate. Over-the-counter foods usually are not restrictive enough. Sometimes, we recommend a vegetarian diet, a home-cooked diet or a hydrolyzed diet. Hydrolyzed means that the proteins and carbohydrates in the food have been broken down into such small pieces that the body cannot recognize them as an allergen. When you do a food trial, you have to remove all unapproved treats and all flavored medications. Patient can even have a relapse when their owner, in a moment of weakness, gives them a piece of food off their plate.


Atopy in animals is from an inhaled allergen that manifests as a skin reaction. Usually these pets lick their feet, scratch at their chest and around their anus and have ear infections. This allergy may be seasonal if your pet is allergic to a certain type of grass or tree pollen, or it may be year-round if he or she is allergic to dust mites or mold. This is the hardest allergy to control. A combination of antihistaminesA drug or other compound that inhibits the physiological effects of histamine, used especially in the treatment of allergies. and immune-suppressing medications like steroids may be used to control the itching. If it is really bad, allergy testing and injections to desensitize your pet (just like in people) may be recommended. Sometimes getting rid of carpet in the house can help. Frequent baths can help remove the allergens from the skin as well.

Secondary Infections

When an allergy causes your pet’s skin to become inflamed, the normal defenses of the skin are broken down. Your pet may scratch and chew, causing small tears in the surface of the skin, aggravating the area. Bacteria and yeast take this opportunity to move in. Once they are there, the bacteria and yeast take over and they cause itching, as well as the formation of small papulesA small, raised, solid pimple or swelling, often forming part of a rash on the skin and typically inflamed but not producing pus. or pimples, making the symptoms even worse. Once this secondary infection had taken over, all the allergies and the other skin diseases can look exactly the same! Diagnosis is made more challenging by the fact that pet can have a combination of allergies and the other diseases at the same time!

There are other causes of skin infections that are not considered skin allergies. Dogs and cats can get fungal infections (like ringworm) from their environment, or a small wound or bug bite matted under the hair can develop an infection. Dogs can get Sarcoptic mange (related to human scabies) or Demodectic mange (red mange), which is generally curable. Cats can get mange as well as eosinophilic plaques, which may recur and need long-term management. Both dogs and cats can have hormone-related diseases that make them susceptible to hair loss and skin infections.


When a veterinarian examines a dog with skin disease, we frequently will want to perform a skin scraping and fungal culture to make sure the problem isn’t caused by mange or ringworm. These diseases require very specific treatments, and we want to rule them out first. Furthermore, if we put a pet with ringworm or mange on steroids and suppress the immune system, we could make the situation worse.

Next, we have to clear up the secondary infection caused by bacteria and yeast. To see if there is an overgrowth of bacteria or yeast we will usually do an impression smear, which means we press a microscope slide or tape to the skin and look under a microscope to see if we need to use antibiotics or antifungals. Sometimes we can do this with shampoos or topical treatments, but frequently we need systemic (oral) medications.

Lastly, we need to make your pet stop itching so he stops causing damage to the skin, which will cause reinfection. We treat that with either topical or oral medications.

Identifying the kind of allergy your pet has is rarely obvious the first time a veterinarian examines a patient. We will often prescribe a few weeks of medication and tell you to come back for a re-check. We need to make sure that the infection is completely resolved so we can figure out what kind of allergy we are dealing with. Unfortunately, many pets don’t make it in for their re-check. Many owners see that their pet is doing better after a week or so of medication, stop the medication, don’t come in for a recheck and call the veterinarian six weeks later saying, “The infection is back. Can I have more medicine?” If we don’t see a pet for their re-check, we don’t know for sure that the infection was 100 percent better. We may have stopped the antibiotics too soon, or we could have a resistant infection. We are never able to distinguish a pattern if we don’t have timely re-checks. It makes diagnosing the cause of skin disease that much harder.

If your veterinarian hasn’t suggested getting to the bottom of your pet’s skin disease, then start the conversation yourself! Just saying, “It seems that Fido has had a lot of skin infections recently. I’d really like to find the underlying cause,” will help us know that you want to go the extra mile for your pet.

Jessica Colborn, DVM, lives in Magnolia, Texas. Dr. Colborn practices as a relief and emergency veterinarian.

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