There are six main categories of dermatitis we veterinarians have to consider whenever a “Skin Case” is presented.  Most skin and coat abnormalities can be defined by or placed in one of these categories:

Environmental Dermatitis - Patients in this category are physically and nutritionally normal, but present with signs of pruritus, hair loss and skin irritation.  By careful discourse with the owner regarding diet, activity, medical history and environment, and by performing a thorough physical exam, the veterinarian can rule out the other categories of dermatitis.  Through the analysis of the patient’s history, the veterinarian will discover that the patient spends time swimming or excavating gopher holes or romping through fields where thistles seem prevalent.  Many dogs are very sensitive to simple lawn grasses.   And by matching what is visible on the patient’s skin with a probable environmental irritant - the cause of the skin problem can be determined and corrective measures taken.   An example is Moist Eczema, often called a "Hot Spot".  (See the photo below-right and more in the discussion of Hot Spots.)  These skin lesions often occur as a result of moisture on the skin surface from rain, pond or lake water. Minute scratches on the skin from, for example, a clipper blade, may trigger other cases.  Especially in dense coated dogs or dogs where there is an accumulation of mats or shedding hair, moisture on the skin may remain long enough to allow superficial bacteria to reproduce (sort of like an organic soup!) and create an infection.  Some cases of Moist Eczema will spread very rapidly and require rather aggressive therapy to correct.  Contact with plastics can create ”Environmental Dermatitis”.

Nutritional Dermatitis - Correction of these cases should be a “no brainer”, but even today, many veterinarians and pet  owners really believe the  “Complete and Balanced” statement on pet food labels. Unfortunately, many dogs and cats live their entire lives in less than optimum health because their caretaker feeds the least expensive food they can find… and feels secure in doing so because of that “Complete and Balanced” statement.

In my thirty-five years of practice, I have seen hundreds of dogs and cats whose lives changed dramatically, and where the pet’s caretakers were shocked and surprised at the remarkable difference in their pets, by the simple act of providing the pet with a high quality, meat-based diet.  Look at Nutrition in ThePetCenter.com for some common sense information about sound feeding principles. Take a look at the photo of a dog in less than optimum health that has been eating a “Complete and Balanced” diet for years.  Without proper nourishment this dog’s entire body, not just its skin and coat, will be continuously in a state of stress. High quality, (more expensive!) meat-based dog foods seldom, if ever, create the kind of skin and coat seen in the photo above.  If you feed dry commercial dog food, be certain that the first ingredient listed is meat such as beef, poultry, lamb or fish.  PetFoodDirect.com displays a number of high quality diets and their ingredient lists, too, so you can compare all kinds of diets for quality ingredients.

Will supplements help?  Absolutely!  But if the diet is a high quality, meat-based brand, the need for supplements is much less critical.  It has been my experience that supplements such a Omega Fatty Acids, Vitamins and table scraps will always help a dog that is eating a generic, commercial dry dog food; and on occasion, supplements may even show positive benefits in a dog eating a high quality diet. Many types of dermatological problems are avoided if the dog or cat is consuming an optimum diet.  In some cases, adding a supplement such as DermCaps, a popular Omega Fatty Acid supplement with a number of beneficial ingredients, is the key factor in avoiding repeated episodes of Hot Spots and other skin afflictions.  If your dog or cat seems to lack good coat and skin health, consider upgrading the diet to a meat-based ingredient formula and adding a supplement such as DermCaps.

Parasitic Dermatitis - The most common response a pet caretaker makes when they see their dog scratching and biting at itself is “I think he’s got fleas”.  And sometimes this guess is correct.  Dark, copper colored and wingless, and about the size of the head of a pin, fleas are big enough that they can be seen scurrying along the skin surface trying to hide within the sheltering forest of fur.  Learn all about fleas here.

There are a number of highly effective and safe flea preventatives your veterinarian can prescribe.  Fleas are ubiquitous, but an understanding of their life cycle, where they hide in the dog’s environment, and utilizing modern pharmacology breakthroughs, no dog needs to be “driven crazy” with pruritus, hair loss, scabs and infections as a result of flea infestation.  See a veterinarian's discussion about fleas at ThePetCenter.com.  Repeated exposure to fleas can trigger a hypersensitivity (an abnormal, excessive reaction) to the bite of even a single flea.  Every veterinarian has been fooled into making a diagnosis of “allergy”, not even suspecting fleas, simply because no fleas were discovered at the time of the physical exam.  This is a classic example of a Parasitic Dermatitis (flea bites) triggering a complicated Allergic Dermatitis (due to the flea saliva).

Interestingly, the all-too-common tick rarely triggers pruritus or allergic reactions, but on occasion will leave an ulcerative lesion that is notoriously slow to heal.  See the photo on the right.  Also see two photos of a tick in action... obtaining a blood meal and severely traumatizing the skin in the process.  Go to photos...

Chiggers, deer flies, and gnats (sometimes called No-See-Ums) can be considered nuisances and generally do not create remarkable systemic skin problems.  Local treatment with first aid ointments generally is successful. 

Cheyletiella mites look like tiny spiders under a magnifying glass and are often called “Walking Dandruff” because upon close inspection it seems like little flakes of dry skin are actually moving about. Partly because they live on the surface of the skin, these tiny critters can be eliminated easily by using any common flea shampoo.  And here’s a creepy thought… Cheyletiella mites can be transmitted to humans where they create, just like on the dog, alopecia (hair loss) with a dry, flaky, slightly pruritic skin surface.

Sarcoptic mites are nasty critters!  Also called scabies or red mange, they create very intense pruritus, alopecia, and inflamed skin with multiple small scabs often present. Sarcoptic mite infestation, more than any other entity, is frequently misdiagnosed as Allergic Dermatitis by even very competent and experienced veterinarians.  There is a good discussion of Scabies in the Exam Room of ThePetCenter.com.  Many veterinary dermatology specialists will not accept an uncontrolled “Allergic Dermatitis” referral case unless the referring veterinarian has first ruled out Sarcoptic mites by actually treating the dog for scabies.  Do as many skin scrapings as you like, you’re not going to find these little rascals because, unlike most skin parasites, these burrow right down into the skin.  (Even ticks simply hold on to the surface of the skin while they feed; ticks do not burrow into the skin.)  Unfortunately, many dogs are treated with cortisone for a supposed allergic dermatitis when in fact these Sarcoptic mites are the cause of the pruritic, inflamed skin... the unnecessary cortisone eventually worsens the situation.

Sarcoptic mites happen to have preferences… certain types reproduce and thrive on dogs, but they do not thrive on other species such as humans. Nevertheless, Sarcoptic mites from dogs can infest humans so if your dog has signs of scabies and you are itching and have little scabs, make sure you see your dermatologist (MD, not DVM)!  Mention your concern about scabies mites.  If your physician makes a diagnosis of scabies on you, your next call should be to the veterinarian to make an appointment to discuss the possibility of Sarcoptic mites in your dog… (the one that’s been getting all those cortisone shots for “allergy”).

Then there are Demodex mites - also called “mange”.  These little rascals do live and reproduce just under the skin surface in the tiny hair follicles and oil glands of the skin.  Unlike Sarcoptic mites, Demodex mites can be seen on a skin scraping viewed under the microscope. They look like tiny cigars with stubby legs stuck to the front half of their body. 

Demodex is most commonly seen in young dogs.  In adult dogs, Demodex cases seem to be associated with individuals that are stressed from disease, poor nutrition, immune disorders or a harsh environment.  There is evidence that many cases of Demodex have a genetically transmitted immune protein deficit underlying its manifestation; the dog’s breeder should be informed of any cases of Demodex mites.  If the dog is otherwise healthy, there are effective treatment protocols for Demodex.  On the “itch scale”, Demodex causes very little pruritus.  On the “baldness scale” Demodex creates mottled and patchy alopecia.

Infectious Dermatitis - Bacterial, fungal and yeast organisms are notoriously obnoxious skin and coat pathogens.   Fungal organisms are called dermatophytes.  One type, called Microsporum canis, causes non-pruritic, circular patches of hair loss, often called ringworm.  Transmissible to other dogs (and occasionally some strains of fungi can be transmitted to humans) your veterinarian can diagnose and treat skin fungal infections in the office. 

Yeasts, most notably a common contaminant of inflamed and environmentally stressed skin called Malassezia pachydermatitis, can irritate an already diseased skin surface. Especially notorious for creating long term, low-grade external otitis, Malassezia does cause pruritus and inflammation.  Yeast infections typically create greasy, odorous and pruritic signs in affected dogs.  The skin is stressed by the waste products of the organisms and responds by releasing histamine - which triggers further inflammation, pruritus and cell damage.  If a yeast infection is diagnosed, there’s generally something else going on such as Hypothyroidism, chronic administration of cortisone medication or dietary fatty acid deficiency.

Bacterial dermatitis rarely occurs spontaneously.  Normal healthy skin has tremendous numbers of a variety of bacteria present all the time.  If something upsets that balance, such as antibiotics eliminating one or two types, the remaining types have a free-for-all!  Anything that damages the normal, healthy, intact skin will hamper the skin’s defense mechanisms.  Any Environmental Dermatitis, such as contact with grass, plastic, an abrasion or moisture, can adversely affect the skin’s defensive barriers and opportunistic bacteria then have their way.  Parasitic damage to the skin will allow invasion by bacteria and trigger the body’s healing defense mechanisms. 

A common affliction of dogs, Infectious Dermatitis often is so irritating that dogs will lick continuously at the lesion and undo any healing that has taken place. A moist, sticky, inflamed skin lesion along with hair loss is characteristic of bacterial dermatitis. These can spread rapidly and even be transposed to other areas of the skin through biting, licking, and scratching of previously uninfected areas.  Lipfold Pyoderma, as seen in the photo on the left, is a classic example of chronic infection affecting the skin.

The treatment for Infectious Dermatitis often includes clipping the hair from the area to allow the air to assist drying. The application of gentle topical medication is helpful as is the administration of oral antibiotics to fight the organisms that are deeply invading the skin.  Yes, cortisone may assist in alleviating the stinging or itchy sensation, but may also suppress normal healing processes.  Whenever an infection is present, the decision to use cortisone needs to be very carefully evaluated.  A better choice may be antihistamines orally.

Allergic Dermatitis - I’ll be honest.  There’s no way to cover this topic in one article.  Veterinarians spend entire weekends and lots of money attending seminars on this topic alone!  It is common, it can be lifelong, it is a challenge to diagnose, and once identified it can be resistant to attempts at treatment.  All the other categories of dermatitis must be ruled out (especially those elusive Sarcoptic mites) before a diagnosis of Allergic Dermatitis can be made. Food ingredients, synthetic and natural fibers, medications and pharmaceutical products, plant material and even dust all can trigger an Allergic Dermatitis.

Even common bacteria on the dog’s skin can provoke an allergic reaction to themselves!  These cases of sensitivity to normal resident bacteria are very challenging to correct.  No matter what kind of allergic dermatitis afflicts the dog, the ultimate cellular cause of the inflammation and resulting “itch-and-scratch-bite-and-lick” activity has a common cause… the release of histamine from skin Mast cells, the deposition of antigen/antibody protein complexes within tissues, the dilation of some blood vessels and constriction of others, the release of toxic chemicals from broken intracellular structures, and chemical and physical irritation of sensory nerve endings.

To what are dogs allergic?  Take a look around you right now.  Odds are that your dog could be allergic to half-a-dozen different substances in the very room you sit; that doesn’t even include microscopic substances in the air you and your dog breath!  Food, carpeting, blankets, dust mites, mold spores in the air, pollen, plastic food dishes, furniture stuffing and ornamental plants all have the potential to trigger an allergic reaction in your dog.  Food allergies are so common that pet food manufacturers have invested millions of dollars in research, development, promotion and delivery of “antigen specific” diets to help in the therapy of dogs with food allergies.

How to allergies develop?  Each individual’s biochemistry is determined by millions of genetic variables.  On occasion, an individual’s various immune responses may over-react to a certain material and “learn” to recognize this substance in case of future contact with it.

The offending agent is called an antigen. Flea saliva is a good example of an antigen that triggers “flea bite” hypersensitivity.   When an antigen makes contact with the dog, the dog’s immune defenses - all primed and ready for a fight since it has previously identified the antigen as an enemy - set to work to disarm the antigen.  Unfortunately, during the course of the battle (called an antigen/antibody reaction) side effects of the battle can cause tissue irritation, inflammation, swelling and cell destruction.  That’s when we notice the dog going into the “itch-and-scratch-bite-and-lick” mode!  There’s a biochemical war going on within the dog!

Immunologists have classified a number of different types of allergic reactions.  Skin and blood tests are common methods of attempting to identify what the patient is allergic to.  Probably the most common type of Allergic Dermatitis seen in dogs is Atopic Dermatitis. This situation is triggered by a number of antigens including inhaled substances such as molds, dust, pollens and other static and airborne microscopic organic substances.  Dogs with Atopy lick and chew at their paws (see photo on right) and scratch their face, eyelids and ears.  This disorder can be very troubling for dogs and frustrating for the owner.  One minute the dog may look and feel normal, the next it will chew its paw or face raw from the intense pruritus.  There is a new product available to treat Atopic Dermatitis in dogs called Atopica.  For many patients, this medication has truly been a "life saver".

Treatment of Allergic Dermatitis includes topical medicated soothing baths, ointments and sprays.  The use of oral antihistamines can neutralize some of the destructive effects of internally released histamine.  More effective in alleviating the discomfort of allergies is cortisone.  This potent hormone, normally secreted by the adrenal glands, can be manufactured commercially.  Numerous derivatives of cortisone are used in pill, injectable, spray, liquid and ointment form. Caution:  If you are sent home with a prescription for cortisone, or your dog has simply been given “a cortisone shot to stop the itching”, your dog may ultimately be worse off than before if the true diagnosis happens to be an unrecognized case of Sarcoptic mites!  Be patient, yes, but be persistent, too.  If your dog is itching, scratching, and licking, or if the skin and coat are not healthy appearing, you and your dog need a diagnosis before treatment is started.

A key point to remember is this:  There is no cure for allergies!  All we can do is avoid the food, material or parasite that is triggering the immune response, desensitize the patient through immune modulation techniques, and assure that the patient is eating a high quality diet.

Neurogenic Dermatitis – This group presents a major challenge to diagnose and treat.  As a veterinarian I know I have  classified a number of cases as “Neurogenic” simply because I have ruled out all the other categories!  There’s nothing left but to blame the poor dog for all that incessant licking and chewing at itself!  The most commonly seen form of Neurogenic Dermatitis is called Acral Lick Dermatitis, Lick Granuloma or canine neurodermatitis.  See more about Lick Granulomas here.

Although rarely seen in cats, in the dog something creates an impulse to lick at a specific area of skin.  Characterized by persistent, obsessive licking and chewing at the target area, lick granulomas may have an unknown origin.  Commonly, though, most cases have a suspected cause such as boredom, separation anxiety, frustration, confinement, or even a minor physical origin such as a tiny abrasion that captivates the dog’s interest.  The dog persists in traumatizing the area, which is usually confined to an easily accessible forelimb, carpus (wrist) or ankle area, and never allows the skin to heal.  Repeated episodes of self-mutilation, partial healing, then repeated trauma and healing, result in severe and disfiguring scarring.  Deep bacterial infections are common and permanent skin damage results.  A Specialist in Dermatology and a Behaviorist may be the dog’s best friends in these cases of Neurogenic Dermatitis.