Allergies: My Approach to the Itchy Dog/Cat

One of the most common things we see at the Kerrville Veterinary Clinic is the itchy dog or cat. Skin issues can be very uncomfortable for the animal and frustrating to the owner. Oftentimes, owners want a “quick fix” and ask for a steroid shot to bring their animal some comfort. While we do sometimes have to resort to steroid shots, we try to avoid them due to side effects. Also, a steroid shot will only mask the itchiness and does nothing to get rid of the underlying problem. There are only a handful of common causes of extreme itchiness. With a little detective work, we can usually figure out the root of the problem and, hopefully, bring both the animal and the owner some long-term relief.

The most common cause of itchiness is an allergy, of which there are four types: contact, flea, food, and environmental (atopy). Bacterial and fungal infections can also cause itchiness, but these infections are usually secondary to an allergy. Scabies, a type of mange, is a less common cause of itchiness. While there are some other rare causes of itchiness, I will concentrate on these most common causes.

My approach to an itchy animal is to try to rule out each possible cause in a systematic order. I can usually rule out scabies based on physical exam. I then try to rule out contact allergy, flea allergy, food allergy, and environmental allergy, in that order.

Scabies (Sarcoptic Mange):
Scabies is a type of mange caused by the Sarcoptes scabei mite. This mite burrows under the skin and causes extreme itchiness! It is also contagious to other animals and to humans. The mite is spread by direct contact. Scabies mites prefer hairless skin, so animals will often have redness and hairloss on their bellies, elbows, and ear tips. Owners will sometimes have itchy red bumps on their chest or arms, from holding the animal. If I see this characteristic hairloss pattern, +/- a rash on an owner, and extreme itchiness then I think Scabies! Scabies is diagnosed with a skin scraping; however, the mites can be very difficult to find. Sometimes, multiple skin scrapings will not reveal any mites, but we go ahead and treat for possible mange anyway, based on clinical symptoms. Treatment usually consists of either topical Revolution or a dip.

Contact Allergy:
A contact allergy is caused by something that actually touches the animal’s skin and causes irritation. The most common contact allergies are caused by shampoos, detergents, or carpet cleaners. Animals that are allergic to a shampoo will often have redness in the armpits or groin areas, as these are places where shampoo tends to not be rinsed off well. Animals that are allergic to a carpet cleaner or laundry detergent will often have redness on their bellies, where the skin is in direct contact with the carpet or bed. Usually, this can be ruled out by looking at the pattern of redness and hairloss.

Flea Allergy:
This is the allergy you hope your animal has, as it is the easiest to prevent! Let me start by saying that this is extremely, extremely common. In Texas, it is not a matter of if your animal will get fleas, it is when. While the flea population is worse in warm/wet weather, we see fleas ALL YEAR round in Texas. Your animal does NOT have to be covered in fleas to have extreme hairloss and itchiness from fleas. Often, we will only find some faint traces of flea dirt on physical exam, yet the animal will have a nearly bald rear end due to a flea allergy. The classic pattern of redness and hairloss for a flea allergy is on the rear end, along the back, and on the backs of the thighs. Cats will often get tiny scabs around their necks.

The first thing I recommend with an itchy animal is quality flea prevention! I tell pet owners to stop wasting their money on the cheap, over-the-counter flea preventions (such as Hartz) or flea collars. Yes, they are cheaper, but they do a much, much poorer job of controlling the flea population. I recommend some of the newer, “quick kill” flea products such as Comfortis , Trifexis, or Frontline Tritak (a newer version of Frontline) for dogs. There is now a “quick kill” product for cats, called Cheristin. These products kill the fleas much quicker than other products, meaning that there is less time for the flea to actually bite the animal and cause the signs of allergies. An animal that is allergic to flea saliva can often have their skin issues completely resolved, just by switching flea products and making sure to give it every month without fail. (This is why I get very happy when I find a flea on an itchy animal!)

Food Allergy:
A food allergy tends to cause itchiness all year round. A food allergy can cause GI upset, as well as skin issues that usually manifest around the anus, feet, neck, face, belly, ears, and tail. People often think that a food allergy is not possible if their animal has been on the same diet its whole life. In fact, allergies usually take time to develop, so it is often something they have been eating for years. A pet can be allergic to anything they are eating, with some of the more common allergens being beef, egg, dairy, chicken, wheat, corn, and fish. (Corn gets a bad rap, but it is not the top food allergy out there)

There is no great test to diagnose food allergies. The easiest way to try to diagnose a food allergy is to put your pet on a 3 month food trial. For 3 months, you must feed your pet a prescription hypoallergenic diet. During these 3 months, you cannot feed your pet treats or table scraps. Your pet cannot eat out of another animal’s bowl if they are on a different diet. I make sure pets are on topical heartworm/flea prevention for the trial, as beef flavoring in oral medications are to be avoided. After 3 months, if the skin has cleared up, then it can be assumed that something in the previous diet was the likely trigger. Some people put their animals back on the old food, to see if they start itching again, just to make sure. The hypoallergenic diets are rather expensive, but they can save money in the long run by decreasing the number of medications/vet visits that are needed.

There are two types of hypoallergenic diets: a hydrolyzed diet and a novel protein/carbohydrate diet. The hydrolyzed diet has proteins that are chopped up into teeny, tiny pieces so that the body does not react to them. This diet works for some animals, but not for others. The novel protein/carbohydrate diet is made up of a single protein source and a single carbohydrate source that the animal has never been exposed to. These are usually something exotic, like venison/potato or duck/pea. The idea is to limit the number of possible allergens, as well as make sure it is something that pet has not been exposed to before. There are some grain free diets out there that frustrate me because they have 4+ protein sources, (EX: bison, fish, venison, lamb, egg) and 3 carbohydrate sources (Ex: potato, sweet potato, pea). An animal that eats this diet will be more difficult to pick out a hypoallergenic diet for, since it has been exposed to so many things.

Environmental Allergy (Atopy):
The fourth type of allergy is an environmental allergy, also called “atopy”. This is an allergy to things like pollen, dust mites, or cat dander. An environmental allergy can be seasonal or all year round, depending on what the pet is allergic to. Patterns of skin irritation are typically on the feet, armpits, flanks, groin, face and ears. It is usually next to impossible to limit an animal’s exposure to an environmental allergen. We, therefore, concentrate on immunotherapy and treating the pet’s symptoms. Immunotherapy can be extremely beneficial in dogs with environmental allergies. In order to do immunotherapy, a blood test or an intradermal skin test is performed, so that we find out exactly what your pet is allergic to. Immunotherapy injections or oral drops are then made up specifically for your pet and your pet’s unique allergies. Allergies get worse year after year, and there is definitely a benefit in starting immunotherapy early on, rather than waiting several years down the road.

As discussed, getting to the source of the itchiness is the best way to help treat your pet. By eliminating that source, you will reduce the allergic symptoms. That being said, allergies cannot be “cured”, only managed. There are several ways to help make your pet more comfortable. First, we must eliminate any bacterial or yeast infections that are contributing to the itchiness. Second, there are several choices of antihistamines and steroids that can alleviate itchiness to bring your pet relief. Third, newer drugs such as Atopica (an immunosuppressant) and Apoquel (a kinase inhibitor) can also provide tremendous relief. Skin allergies can be extremely frustrating. Having an itchy pet can, oftentimes, leave owners feeling helpless. Please let us know if we can be of any help.

Dr. Ryan Roberts