common pet allergies in dogs and cats

3 Common Pet Allergies


There are 3 main allergies that dogs and cats are affected by:

  • Flea allergies
  • Food allergies
  • Pollen allergies (inhaled and topical allergens that include dust and molds, also called Atopy)

Allergic animals generally have an “itch threshold”. Once their allergic stimulants cross that threshold, then they itch, scratch, chew and break out with secondary skin infections. It is not uncommon for allergic animals to be affected by more than one type of allergy. Pollens are the most difficult to deal with and are often the last to be ruled in or out.

Any allergic animal should be on a strict flea control program year round and have undergone a food trial to help avoid any trigger foods.

We can do nothing about the pollen in the environment but we can control the flea and food exposure. Very often if fleas and food allergies are dealt with, then the pollen allergies drop below the “itch threshold” or at least become much more manageable.

Secondary infection is a common problem with any allergy and can be a large contributor to the ‘itch threshold’ all on their own. All animals, just like people, have normal resident bacteria and yeast on their skin. During an allergy flare up when the skin is inflamed, then all those hair follicles can become infected. Skin infections are itchy all by themselves, beyond the itch factor of the inciting allergy. So watch closely for signs of moth eaten patchy appearance to the hair coat or crust and scale build up next to the skin, and/or red bumps or circular discolored areas on the skin. Get used to parting the hair and looking at the skin, as well as looking in the ears and on the belly and beneath the “arms” where you can see the bare skin more easily. When a reasonably well controlled animal is having problems maintaining that control then very often secondary infections are the source of the problem. Once they are cleared, then the routine control measures often work well once again.


The diagnosis of what type of allergy your animal has is involved and may take time over the course of a year to see what, if any, patterns are involved in the allergic flares.  Food allergies are commonly non-seasonal and appear year round, but if the offending ingredient is only occasional treats, it can appear to wax and wane. Pollen allergies usually start seasonally but may progress to become a year round problem for any pet as well. Pay attention to things like seasonal appearance, even thinking back to when the dog was young. Also try to be aware of any changes that may have occurred that coincide with the onset of the allergic flare (new food, new treats, new bedding, etc). Patterns of hair loss are not as specific as one might hope to help but a very rough guide is that flea allergic dogs usually have their worst areas over the rump and down the back legs. Foot chewing, and rash on the belly and underarms can be associated with pollen allergies as well as food allergies. Face rubbing and recurrent ear infection are often associated with food allergies a little more than the others. Recurrent hot spots can occur with all three – flea, food, or pollen. Cats often manifest the same pattern regardless of the cause of the allergy – ventral hair loss on the belly and scabs and crusting across the entire body, particularly head and neck.

Flea Allergies

Of the three, by far, the most common culprit is flea allergy. If an animal is not allergic to fleas then they seldom scratch or lose hair, even if they are covered in fleas. If they are allergic, then there are a certain number of bites they simply cannot tolerate. Beyond that number of bites, then the inflammatory cycle kicks in for the allergic animal and they begin to scratch, bite, chew, and lick excessively. Cats are extremely difficult to identify even a low level of flea exposure. Their routine normal grooming habits will result in no physical signs of fleas whatsoever in a mild infestation. A flea allergic cat that grooms excessively will remove nearly all signs of even a moderate infestation daily from their body. If you see fleas on a cat with patchy hair loss (meaning it excessively grooms) then you have a huge infestation in the environment! Much of the same is true of a flea allergic dog, in that it is very common to never be able to physically identify a flea on them due to excessive grooming behavior.

The moral here is IT DOES NOT MATTER WHETHER YOU SEE A FLEA or not! Another common misconception is that fleas cannot live in a house with hardwood floors. While it is much easier for them to get a solid foothold in a carpeted house due to the sticky nature of the pupal cocoons, they are perfectly capable of maintaining a viable infestation on solid flooring surfaces as well. If you have an allergic animal it is in your best interest to undertake a serious flea control effort even for “purely indoor” cats. If the animal walks outside then it is exposed to fleas, plain and simple. You can bring an occasional hitchhiking flea indoors as well. There is not enough paper available to describe the number of times fleas have been found on cats that have never stepped outside a single time in their entire lives.

If your animal is actually flea allergic then it is a must that they stay on year round flea control measures. The slightest break in flea control can make for the development of a viable flea population indoors to aggravate the animal’s allergies year round.

Food Allergy

The next step for working through most allergic causes of skin disease is a serious look at food allergy and beginning an actual food trial. Animals can develop allergies to foods as they age just as well as they can be born with intolerances, thus they can become allergic to a component of a food that they have been eating their whole life with no previous problem. Food allergies are notoriously much less responsive to steroid injections than either flea or pollen allergies, and so when animals begin to require more and more steroid intervention to manage their allergies then often food allergy begins to be suspected as a culprit. Before undertaking a trip to the dermatologist or pursuit of expensive antigen and injection trials for an allergic animal, it is always wise to conduct a food trial.

A food trial should last for 3 full months on specific restrictive content foods with no treats, and no table scraps. If you haven’t done something that strict, then you haven’t even begun to rule out a food allergy. Before continuing to throw money, time, and effort against the wall of allergic problems, then it is vital to make certain food allergies have been ruled in or out definitively.

Pollen Allergy

Pollen allergies range from mild seasonal problems to severe year round issues. Most commonly they at least start as a seasonal problem. These dogs benefit from routine supplementation with omega 3 fatty acids (found in fish oil or flax seed). They may often be managed with routine antihistamine usage and occasional uses of steroid during their bad seasons. Some pollen allergic dogs are so severe, so often that they must be tested to see what specific pollens and molds they are allergic to and then take a true “allergy” shot, which is made up of the antigens (allergic stimulants) that they react to most, to try and desensitize their system to them. Severely pollen allergic dogs will often benefit from seeing a skilled veterinary dermatologist, but before that expense is undertaken, the dermatologist and the owner’s wallet will wish to have firmly ruled out flea and food allergies.

Dogs and cats are walking through the thickest layer of pollen, dust, and mold there is as it collects low to the ground. Thus they are exposed to the allergens via skin contact and inhalation much more than we are. Also, they don’t change clothes and take a bath every day to get rid of the allergens they are in contact with like humans do. Any of the commonly recommended strategies for air purification may assist. More routine washing of their bedding can help. Some owners report improvement when they wipe the coat and feet down with a moist washcloth or hand towel after the dog has been outside. Dust allergic dogs may be further helped by having food sealed in air-tight plastic containers.

Antihistamines often help but remember just like with people, some dogs respond better to one antihistamine than another. Dog and cat antihistamine dosages are wildly different than human dosages so please call for specific recommendations on different antihistamines. The majority of pollen allergic animals can be managed well, but it does require diligence on the owners’ part and early intervention when they have flares.

In conclusion, there is no quick fix for pet skin allergies. They require attention and maintenance care on the owner’s part for the life of the pet. Judicious, occasional steroid usage is a fine band-aid when things spiral out of control, but constant steroid usage will cause more problems than it solves in the end for the health and quality of the life of the animal. Recognizing and managing all the contributions to the “itch threshold” will provide healthier, happier long term management for the animal as well as the owner’s pocket book.