Skin Allergies, Atopy, Allergic Dermatitis, Inhalent Dermatitis, Miliary Dermatitis and similar allergic skin problems in the Dog and Cat

Roger Ross, DVM


One of the most common and most frustrating problems in small animal medicine ... for vets, for pet owners, and for pets ...  is


The main reason this disease is so frustrating is because ... as of yet ... we don’t have an easy cure.

Here’s what you need to know:

For treatment reasons, we vets usually separate the different types of allergies into several big categories such as:

Allergic Skin Disease due to fleas and other external parasites

Allergic Skin Disease due to food sensitivities

Allergic Skin Disease due to contact irritants

Allergic Skin Disease secondary to infectious agents like bacteria, yeast, or fungus  (This might be confusing, but skin infections of various types are often secondary to other words, the allergy came first and made the skin so red and irritated that the damaged skin became infected later.  But it can happen the other way around too: the infection comes first and the skin has an allergic reaction to the yeast or bacterial waste products in the skin.)

And the biggest category: Allergic Skin Disease due to inhalant allergens.  We call this disease ATOPY

Mildly interesting note:  When I was in veterinary school, we were taught that "Atopy" was a Greek or Latin word (I forget which) which meant something like unexpected placement and we used the term to describe skin disease that was caused by inhalant allergen particles like pollens, molds, and microscopic little dust mites.

The idea being, that, at least when the link between an animal breathing in some little particle into the respiratory system was first discovered to be the cause of itchy skin disease, well, it was unexpected.  We still don't fully understand all the details of why this happens, but we've got a pretty good understanding about how allergens can affect the immune system.

At any rate, the name has stuck.  One more thing; until recently, atopy referred to skin allergies caused mostly by inhalant allergens.  By the way, most of the other names in the title of this page above basically refer to the same disease.  I say until recently, because now we're being taught that the problem isn't just caused by inhalant allergens but also by allergens that enter the body through skin contact and end up causing an allergic reaction in areas of the body other than where the contact occurred.

Allergens of different types are EVERYWHERE ... little pieces of protein, pollens, dust mites, molds, and God knows what invading our sinuses, eyes, lungs, ears, and skin.

Our immune systems respond.  Sometimes to excess.  Just one of the things that happens is that the body’s immune system releases mast cells to fight off the invading allergens.  Inside the mast cells are several potent chemicals (histamine, serotonin, prostaglandin) designed to destroy the invading allergen.  We’re talking about microscopic biological-chemical warfare.

We humans have a lot of mast cells in our sinuses and respiratory system, so if we have allergies (over-responsive immune systems), we tend to have respiratory symptoms. 

Dogs and cats have mast cells in their respiratory system too, and can also have respiratory symptoms ... BUT ... they have lots more mast cells in their skin and are much MORE LIKELY to have skin allergies.

With dogs, anywhere on the skin may become red and irritated, but the most commons areas to become sensitive are the ears, lower legs and paws, and the tail head and crotch area.  One of my professors (Dr. Ed Rosser) referred to this as "Ears and Rears".  This pattern is also common with food allergies.

With cats, the most typical signs are multiple little scabs around the neck and head and along the center line of the back.  We call this condition of multiple scabs miliary dermatitis. We now know that this is the same disease as atopy.

The immune system is quite complex, not nearly as simple as I’m about to outline, but here’s what going on:

The skin is exposed to some allergen that the pet is sensitive too. This may be a grass pollen, a mold, or whatever.  These problems are often seasonal.

Why some pets are more sensitive than others?  We don’t know for sure. 

Genetics are involved.  Certain breeds are more likely to be sensitive than others. 

Skin type and skin chemistry is involved.

Pets that are sensitive to one allergen seem to be more likely to be sensitive to other allergens.  More sensitive to some foods.  More sensitive to fleas.  More sensitive to drug reactions. And so forth.

We know that stress and anxiety are factors.

We know that sex hormones, thyroid hormones, and sebaceous glands are factors.

Are you with me so far?  Summary: For reasons we don't fully understand, some individuals are very sensitive to foreign material when it enters the body and over reacts by releasing mast cells full of destructive chemicals and proteins called immuno-globulins.

The potent biological chemicals in the mast cell not only destroy the allergen but also irritate the surrounding tissue causing heat, pain, and inflammation. 

This in turns irritates the glands in the skin, and when irritated, they produce more sebaceous goo and other secretions.  The skin, by this time becomes itchy.  The skin bacteria thrives on red, itchy, irritated skin with pores clogged up with excessive glandular they multiply.  And multiply.  The skin may then become allergic to all the bacteria waste products secreted by the large number of skin bacteria.

This scenario of skin inflammation in response to an allergen ranges from mild to severe.

So, what can we do to help?


We don’t have a cure for Atopic skin allergies, but here’s what we can do to manage these cases and make your pet a lot more comfortable.  Note that it's not a realistic goal to stop 100% of the itch but rather to control the problem enough to make the pet reasonably comfortable.

Here we go, all the reasonable options.  Usually a combination of the following are needed:

1.  A few basics:  Minimize the irritants affecting the skin. This means making sure that there aren't any fleas or ticks affecting your pet.  Fleas really sensitize the skin making it hyper-reactive to other allergens.  Please go to our parasite page and read about how ineffective many flea products are.  You may have to get aggressive with flea control.  In addition to fleas and other obvious parasites, some pets are also irritated by the simple build up of body oils and dirt.  Frequent bathing in the right shampoo may be needed.  Go to my shampoo page for more information.

You should also make sure ringworm fungus isn’t present which can hyper-sensitize the skin.  Your vet may very well recommend a ringworm culture for this reason.

You also need to make sure there aren’t any internal parasites present.  They can also sensitize your pet’s immune system.  Your vet may recommend a fecal test for intestinal parasites and a blood test for heartworms.

2.  Good nutrition: Inexpensive or inappropriate diets frequently lead to poor skin health making skin more vulnerable to inflammation.

We will talk about actual food allergies in a little bit.

3. Grooming and cleaning.  Often extremely helpful in keeping the skin healthy, the pores clean and unclogged, in moisturizing and helping damaged skin to heal, and controlling the secondary yeast and bacteria that otherwise complicated skin allergic diseases.  Refer to my "Shampoo" page

4.  Antihistamines: generally safe, inexpensive, and helpful ...but usually not helpful enough to solve the problem.  Sometimes if one antihistamine doesn’t help much, we’ll try another type with success.  Even though antihistamines alone are often not enough to stop the itching and skin irritation, in combination with other treatments they may be an important part of the solution.

5. Omega 3 and omega 6 fatty acid supplements: Dramatic improvement in about 25% of cases and helpful in about 75% of cases.  Well worth a try.  No adverse side effects known.  Omega supplements of differing quality are sold everywhere, but it's fairly important to get the right ratio between the the different types of fatty acids for best results. 

6.  HypoAllergenic Food Trials: food allergies are not the most common cause of skin allergies in dogs and cats ... but food allergies are frequently a part of the problem.  You see, once a pet’s immune system is stimulated by one type of allergen, it seems to become more sensitive to other common allergens.  Hill’s, the maker of Z/D diets, synthetic protein foods designed for food allergic patients have done studies that indicate that 2 out of 3 itchy dogs - regardless of cause - improved when fed their hypo-allergic diet.  Note: you have to be patient and feed hypo-allergenic diets for at least 3 weeks ...exclusively (no treats that might be allergenic, no gelatin capsules that contain animal proteins, etc) before expecting results.  You should really take the time to talk to your vet about picking an appropriate trial diet.  There are a lot of food trial failures because people don't think about things like meat by products, animal fats, modified food starch, bone meal, and vegetable oils (soy and corn are common food allergens and the cheapest, most common type of vegetable oil is made from guess what?)  There are quite a few prescription diets available to choose from at your vet's and well worth buying these diets specifically designed to test for food allergies.  Just buying any brand of lamb and rice diet, for example, won't help if it also contains some of the other ingredients listed above.  Another option is feeding a homemade diet... again best planned out with your veterinarian.   If food allergies are a major part of your pet's allergies, and we choose a right test diet, usually we see significant initial improvement within about 3-4 weeks.  Once were prove that your pet is allergic to one type of food, we can experiment with different diets until we find the best one in terms of effectiveness on the one hand and price, convenience, and flavor on the other.

7. Steroids: (Prednisone, dexamethasone, methylprednisolone tablets and injections)  Hoo boy.  This is a touchy subject.  In the vast majority of allergic skin cases, NOTHING works better than steroids. 

They’re fairly inexpensive. 

And they’re usually really effective at minimizing the itch, pain, and inflammation.

They’re usually very appropriate (and safe) for short periods and often allow us to greatly improve the situation, stop the itching, and permit badly inflamed skin to heal.  They tend to work much faster than alternative treatments, so they can be used in conjunction with other treatments giving the pet relief until other treatments have time to "kick in".

They're somewhat diagnostic: if steroidal treatment doesn't help as much as expected, that's a clue that skin allergies may NOT be the main problem. 50% of food allergies, for example, don't respond to steroid treatment, and some itchy diseases such as ringworm and bacterial infections can sometimes become worse with steroids.


Many vets feel that steroids are over used and that we vets that use them regularly do so as a quick fix and under-estimate the potential harm we may be causing our patients! 

Well, it’s true that steroid therapy has a lot of potential risks.  I, like many vets, feel the benefits greatly outweigh the dangers in many cases...especially for short term use, but here’s a list of the potential problems:

a.  steroids make patients drink more and urinate more

b.  sphincter muscles to things like the urethra are relaxed...patients with borderline incontinence might start leaking again.  Bacteria might more easily invade the bladder.

c.  steroids suppress the immune system ... this is great for allergies ... but too much immune suppression prevents the immune system from fighting off infections.  Since bacterial skin and ear infections are often present secondary to allergies, this is a real potential problem.  In practice, this problem is usually prevented by limiting the use of steroids to short periods and further countered by using antibiotics at the same time.

d.  steroids, especially if used long term affect most metabolic systems in the body and patients that have been treated with steroids have a higher future chance of getting diabetes, adrenal gland problems, and liver and kidney disease.  Serious stuff.  Luckily this rarely happens with short term use; your vet will probably go over the potential dangers of steroid use with you if he/she thinks they are warranted.

e.  steroids stimulate appetite and pets on steroids for long periods often gain weight.

f.  steroids can cause abortion, so we certainly avoid their use in pregnant animals.

g.  as a rule, cats are much less likely to have serious side effects from steroids than dogs and humans.

h.  the only other problem I can think of is that steroid use can also screw up blood test results especially skin allergy testing for several weeks after stopping the steroids.  A bit of a nuisance.

Often we find that if you treat with steroids for 5-21 days giving the inflamed skin time to greatly improve, then non-steroidal treatment such as antihistamines and bathing and omega 3 fatty acids will then be adequate for control whereas they would fail to provide adequate relief if not also given steroids for a short while.

A couple more notes about steroids:  Some cats can't convert prednisone into prednisolone...the active form of the drug, so in cats I recommend using prednisolone to prevent this mishap.  Even more often, I use injectable methylprednisone in cats because it's so convenient compared to pilling a cat.  And finally, for reasons we don't understand, if your dog gets inconvenient or excessive side effects ... such as incontinence ... on one form of steroids, switching to another form ...say from prednisone to dexamethasone tabs ...often relieves the problem.

Alternatives to steroids:
You'll see that most have problems of their own

8.  Pentoxifylline (Trental) belongs to a class of drugs called phosphodiesterase inhibitors.  At higher than official doses  this medication was effective in SOME dogs in reducing skin inflammation and itching.  It can be used synergistically with either steroids and/or antihistamines.  The drug is more effective (better absorbed) when given with meals. Side effects are rare and usually minor.  May not be safe for cats though.  Other drugs in this class (Papaverine and Arofylline) haven't worked as well or as safely.

9.  Leukotriene Inhibitors such as Zileuton (Zyflo) or zafirlukast (Acculate):  don't seem to help much in most cases, but I mention this because they have been effective and safe in human cases of atopy.

10.  Misoprostol (Cytee): is a prostaglandin hormone analog that works fair, not great, in some dogs but it's not only quite expensive but it causes GI upset in a large number of patients.

11.  "Tricyclic" Anti-Depressants:  these medications, common for treating depression and emotional problems in people just happen to be potent blockers of H1 receptor sites which play a role in itching.  This is an off label use of these medications but seem to be safe for most pets.

12.  Cyclosporin (Atopica) is fairly new to veterinary practice and about as effective as steroids WITHOUT THE POTENTIALLY BAD SIDE EFFECTS.  It's also effective and safe for cats and good for granulomas.

Comments:  GI side effects are fairly common but usually mild
Despite FDA recommendations, this drug works fine and with fewer upset stomachs if given with food.

Very Expensive ($100-200/month) although many dogs can be controlled on small doses after the initial month or two

So, What to do?

If the pet isn't too miserable, it would be nice to do the food trial first.  If it works, a special diet may be the main solution.

Otherwise, we typically combine shampooing if possible, antihistamines, omega fatty acids, flea control if needed, and some form or steroid for a short period (or not for those opposed to steroid use).  This usually works out well in most cases, and then we can attempt to get the pet off steroids.  Keep the steroids on hand for flare ups.

And When That Doesn't Work?

A quick comment:  failure is often because owners aren't willing to put much effort or expense into solving the problem:  It's too much trouble to give frequent baths.  They can't give pills to their dogs.  The Omega Fatty Acids are too expensive.  They resent paying more for special diets.  And a lot of owners are in DENIAL about fleas.

An even more common cause of failure, though, is that there's something additional going on...typically a bacterial, ringworm, or yeast infection.  If we can figure this out, usually we can finally get adequate improvements.

But if all of the above fails, or the use of steroids if unacceptable, there's another option:

Allergy Testing and Desensitization is often successful.  The biggest problem is expense and unless your local vet is skilled and set up for this treatment option, it usually involves frequent trips to a skin specialist.  In our area that means an hour trip each way to the big city of Greenville, and a lot of time off work.
Your vet will go over the details of this option.

Isn't There Any Thing Else That Works?

Whenever we have a situation where there isn’t a terrific treatment (effective, inexpensive, and safe) for a problem, you will find lots of “alternative” treatments, holistic treatments, herbal treatments, and so forth being touted as the best thing since sliced bread. 

High doses of anti-oxidants might be helpful, for example. 

At any rate, be cautious about what you believe.

Here's a list of previously touted medications that we're pretty sure don't work for skin allergies:  Vit C, Doxycycline, High Dose Vet E, Aspirin, tetracycline/niacinamide, Zinc methoinoine, Dilantin, homeopathic treatments (Homealot). 

As far as herbal, Chinese secret recipes, and acupuncture are concerned...well, you're on your own.  I'll believe it when legitimate, repeatable, research papers are offered.  A lot of information and mis-information needs to be sorted out yet.

This page is devoted to skin allergies in dogs and cats.

This is also known as "Atopy" or "Atopic Dermatitis"

In cats, we sometimes call this "Miliary Dermatitis"

On Other Pages in This Section about skin problems:

Introduction To Skin Diseases

What To Expect When You Go To The Vet with a pet suffering from skin disease

Skin Allergies Caused by Food

The Therapeutic Diets we recommend for treating intestinal, ear, anal gland, and skin disease due to food allergies

Mange, Demodex, Demodecosis,  Sarcoptic Mange & Ear Mites

Fleas, Ticks,Flea Sensitivity, FBD, & Flea Bite Dermatitis

Miliary Dermatitis

Ring Worm

Hormonal Skin Diseases

Bacterial Skin Diseases: Pyoderma
Folliculitis, Hot Spots

Malassezia and Yeast

Contact Allergies

About Lick Granulomas in Dogs (Rodent Ulcers, aka Proud Flesh)

Eosinophilic Granuloma Complex in Cats

Anal Gland Problems

Seborrhea, Dandruff, and other flaky, scaly skin diseases

Stud Tail

FoxTails or Fox Awns

Immune mediated Dermatoses

Feline Symmetrical Hair Loss (Alopecia)

Porcupine Quills

Fly Strike

Hookworm Dermatitis

Our shampoo Page ...chosing an appropriate shampoo

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