Environmental Allergies (Atopy/Atopic Dermatitis)
By Emily Hoppmann, DVM
An allergy to substances in the environment is also called Atopic Dermatitis or Atopy and the substances that can cause this allergic reaction are called allergens or antigens. Environmental allergies, or atopic dermatitis, are a common problem in dogs and cats and is even more prevalent in the Southeast United States. It is more common in dogs than cats and the treatment plans for each species are often much different, but the underlying disease process is the same in all species (even humans). It is most likely that there is a genetic basis (something that is inherited from a pet’s parents) since it occurs more commonly in certain breeds and lines (such as Labrador Retrievers, Spaniels, Terriers, etc.). Allergens that are well recognized triggers for atopic dermatitis include pollens, molds, dander (shed skin cells), house dust, tobacco smoke, and a variety of other substances. Our pets are typically allergic to the same things that we are and so they will often have flare-ups at the same time our allergies are bothering us. What each pet is allergic to is very individual though and often can change depending on the location of the pet and, also, tend to get worse with age.
The primary symptom of environmental allergies is itching, and the problem typically first becomes apparent when a pet is between 6 months and 3 years old. Early symptoms in dogs may be mild and can include foot-licking, face rubbing, ear problems, and scratching behind the elbows, all without any visible reason (no visible fleas, no plant material caught in the haircoat, etc.). The two biggest symptoms are licking at the paws and chronic ear issues/infections. The problem is often seasonal since the substances in the environment change with the seasons – the worst times for most pets are April through October. As time goes on, the allergy worsens and more areas of the body become involved because the pet is exposed to the substances more and more often, which allows the body to react faster and faster. Itching that at first occurred only seasonally may become present all year round as the pet’s body goes into overdrive attacking substances in the environment.
Environmental allergies in cats can be more difficult to diagnose and cats can show several different types of skin problems. This can include hair loss on the abdomen and inner thighs or on the back from overgrooming (licking, chewing) due to itching; while others may scratch around the face and neck. A condition called miliary dermatitis may develop, where small crusts (scabs) can be felt through the hair coat on the surface of the skin. This disease was named because the small crusts feel like little grains of rice (such as those that are produced from mills). Eosinophilic granuloma complex is another manifestation of allergies in cats and signs include raised, flat, reddened areas (plaques) on the skin or sores on the upper lip. This complex can also attack the mouth of some cats and cause a great deal of dental disease and oral pain.
Diagnosis of environmental allergies may be challenging because many other types of skin problems produce the same degree of scratching, hair loss, and redness of the skin. To reach the conclusion that environmental allergies are present, a combination of elements usually needs to be present:
• The typical history of the onset of the itching (often seasonal, since pollens are a common cause of atopic dermatitis)
• Finding a typical pattern of skin lesions over affected areas
• The exclusion of other causes of itching
• A known response (or lack of response) to certain types of treatment options
I use a thorough physical examination and often will need to perform several tests to rule out other skin problems such as mange mites, ringworm, bacterial infection, or flea allergy, any of which can cause itching and scratching that is identical in initial appearance to environmental allergies. There are often multiple factors at play since a pet with environmental allergies usually develops some of these other skin problems as a result of the skins normal defense being weakened. Once a pet has been diagnosed with environmental allergies, treatment is started to control the allergies (help with the pet’s overall comfort and relief of itchiness) and to treat the secondary skin issues. There are advanced tests that can be conducted to determine which substances in the environment are triggering the allergy in order to remove them or desensitize your pet to them as part of treatment – these advanced tests include intradermal skin allergy tests and blood allergy tests. Blood allergy testing is a much easier test to run, but the results are much less accurate or helpful. The blood does not react to allergies the same way skin does, so I prefer to do intradermal skin allergy testing if further testing is done. However, these advanced tests are expensive and the results are usually used in an effort to create individualize allergy shots (just like in people) to help with the treatment. Unfortunately studies have not shown that allergy shots are all that effective in most pets; meaning that even a pet who has undergone allergy testing and is receiving allergies shots, often has to stay on the same type of medication that he was previously on. However, in severe cases that can’t be managed with medications a referral to a dermatologist and potentially receiving allergy shots are options that can be explored.
The most frustrating thing for pets, owners, and myself (as the treating veterinarian) is that environmental allergies cannot be cured and usually get worse with age. This means that all efforts are directed at managing your pet’s symptoms so that they have a comfortable, happy quality of life. Environmental allergies can be a profoundly frustrating disorder both for the pet and the owner, since relentless chewing and licking can be intensely bothersome to both. However, with a proper diagnosis, dedication to staying on top of a pet’s allergies and symptoms, and appropriate treatment for the allergies and any secondary skin issues, many pets with environmental allergies become comfortable and lead normal lives.
Several approaches can be taken for treatment. If steps can be taken to minimize exposure to the allergens in your pet’s environment this should be done, such as to eliminate dust, molds, excess dander, etc. in the home. However, many allergens cannot be avoided (such as pollen from plants or trees), so it is up to using medications to provide relief. However, even with pets with known environmental allergies it is also important to look for other problems that may be contributing to the itching. Often times a pet will have a flare-up where the clinical signs become worse due to a secondary issue, such as a skin or ear infection (which can be due to bacteria, fungus, or a combination of both), and this issue needs to be addressed or it the secondary infection can make the clinical signs of the allergies even worse.
Many pets with environmental allergies have allergies to multiple things including allergies to food, contact allergies, or flea bite allergy. These allergies compound the symptoms of itching and scratching so if you notice a change in your pet’s clinical signs it is important to see if your pet has an allergic disorder beyond environmental allergies so that all triggers can be avoided as best as possible and treated appropriately.
Skin that is inflamed due to scratching and chewing from environmental allergies is prone to bacterial and yeast infections that can themselves also cause even more itching because they are irritating to the skin as well. A good physical exam and different testing of a sampling of the surface of the skin (which can be done through skin scraping or tape preps of the skin and then the harvested skin cells can be examined under a microscope) can identify whether these complications exist. If these opportunistic infections are present, antibiotic or antifungal treatment is necessary to help limit any more damage to the skin and help get your pet comfortable and itch-free. Just as it is important to treat opportunistic infections, it is important to eliminate as many causes of itching as possible (such as fleas, food allergies, and contact allergies) in order to control a pets’ symptoms.
Several medications are used for treating itching caused by atopic dermatitis or allergies in general. Antihistamines are helpful in some pets, but generally the over the counter products such as Benadryl are not strong enough to eliminate the itching and other human products are actually dangerous to your pets. It is best to use an antihistamine that is pet specific to have the maximum affect and not risk having any harmful or adverse affects from over the counter medications. Omega-3 fatty acids can help ease skin inflammation and these can be provided in food and as supplements. There is a difference in how well the body of your pet can take in and use different sources of Omega-3 fatty acids, so this is an important topic to discuss with your veterinarian. Many people think of corticosteroids, such as prednisone, to reduce inflammation and itching, and while this type of medication can be very effective, it is a powerful medication with serious side effects. I use very few, if any, steroids to manage allergic conditions because long-term and/or high-dose treatment with steroid medications limit the skin’s natural defenses and allows opportunistic infections, such as sarcoptic mange and bacterial or fungal infections, to develop. Also, the use of steroids can have serious life-long consequences, such as cataracts, pancreatitis, and a decreased life span. There are a wide-variety of medications that are available to help manage allergic conditions in pets and every patient is unique and will need a very individualized approach. Often time it takes some degree of trial and error to find the best combination for your particular pet that does the most good, with the fewest side-effects.
Some important things to keep in mind:
• Realize that tests are needed to look for skin disorders that mimic environmental allergies, and to look for complicating or secondary disorders that are occurring on top of primary environmental allergies. The value of these tests lies in identifying anything other than the environmental allergies that would require a specific, different treatment.
• Realize that environmental allergies (also known as atopic dermatitis) themselves are often a diagnosis of exclusion, meaning it is the explanation for itching and scratching when no other cause can be found, but there are several classic clinical signs that I am looking for during my physical exam. Also, knowing as much background information on the issue is helpful so getting a good history from you is also very important
• Give all medication exactly as instructed and be sure to make your follow-up exams as scheduled or call to see if you should refill your medication if you are not going to be able to make your appointment before you are out of medications. It is critical to be able to check certain conditions while an animal is still on medications or it is like starting all the way over from the beginning and that isn’t fun for anyone.
• If there are substances that you know are triggers for your pet that can be avoided, but sure to avoid contact with these allergens as much as possible. For example, if fleas trigger an allergic response in your pet it is critical to be on a monthly flea prevention from your veterinarian and have the house and yard treated by products your veterinarian can recommend.
• Don’t assume that “cortisone pills or shots” (steroid) are the only or best solution to treating an allergy. Although the simplest and most effective in the short term (and the only option year and years ago), the benefits of this type of medication are almost always outweighed by the serious, non-reversible, health problems they cause in the long term.
• Always call your veterinarian to schedule an appointment if symptoms suddenly worsen or you notice signs of ear disease (head shaking, pawing at ears, pain on touching ears). This may be a sign that the underlying environmental allergy has caused a secondary infection of the skin or ear.
• Since allergies can be an inherited condition, pets affected with this disease should not be used for breeding.