ATOPIC DERMATITIS IN DOGS
What is Atopic Dermatitis?
Atopic dermatitis is an allergic skin disease of dogs which is caused
by immunological hypersensitivity to common substances in the
environment such as house dust mites.
What is allergy?
The immune system of mammals makes receptor proteins (antibodies) to
substances that are foreign (i.e. not part of the body), each antibody
being specific to a given substance.
are of several types, IgG for instance being involved in protection
against viral diseases after vaccination whereas IgE, involved in atopic
dermatitis, is particularly concerned with protection against parasites.
IgE antibodies coat specialized cells (mast cells) in the skin where
they sit waiting for contact with the parasite proteins to which the
animal is sensitized. If the substance is encountered, perhaps as a
result of a burrowing mite, the mast cell releases chemicals (mast cell
mediators) which try to destroy the invader. In allergic animals this
whole system is oversensitive and the release of mast cell mediators in
the skin occurs inappropriately to apparently innocuous substances such
as pollens, moulds and house dust mites (figure 1).
For allergy to be apparent, dogs need to be first
"allergic" and then be exposed to substances (allergens) to
which they can develop the abnormal immune response. The most common
source of allergens is the house dust mite. These tiny creatures live in
all of our houses, in carpets, beds and other soft furnishings and feed
on skin scales that are constantly falling from people and animals. They
litter our environments with fecal pellets of half-digested food and
digestive enzymes and it is these minute fecal particles that contain
the most important allergens. Dogs can also become allergic to pollens
and moulds although this is much less common, presumably because of less
Atopic dermatitis is often first apparent in the first two years of
life. Owners may notice that the dog grooms excessively, with licking or
chewing of the paws, abdomen and perineum. The ears may be reddened and
hot to touch even though not scratched. The result of this itchiness (pruritis)
is that the dog will often be presented a number of times in the first
eighteen months of life for a variety of seemingly minor skin
conditions. Between these episodes the skin and the coat can look
remarkably normal. Spots, acute moist dermatitis, ear infections and
scratching may all seem to occur independently and it is only in
retrospect that a consistent pattern of disease emerges. As the
condition becomes more severe, pruritis dominates the animals' life and
specific anti-itch therapy becomes necessary. With increasing pruritis,
baldness (alopecia) and redness of the skin become evident and secondary
infections with yeast or bacteria become more common.
Clues to identify unseen itch
Many people scold their dogs for scratching, almost without
realizing. Slowly we train our pets to be quiet and all but the most
itchy will choose to scratch and chew in private.
there are some tell-tale signs that help us to identify the pruritic
dog. Saliva staining is a commonly-seen feature in these animals. A
red-brown staining of light colored hair is often seen in allergic dogs
in the groin, arm pits (axillae) and between the toes (interdigital
spaces) and can be seen in figure 2. In addition, with long term
problems, the skin itself will also change color. Instead of being pink,
a black mottling (hyper pigmentation) will slowly develop, especially if
the skin has looked red at the site. This is most commonly seen on the
At present there is no definitive test that will absolutely confirm a
diagnosis of atopic dermatitis. Because this is the case, veterinary
surgeons may suspect atopy after examining a patient, but have to make
sure that other causes of itch are not present. Once these have been
ruled out, skin testing can be used as a pointer to the allergies
So what are these other diseases? Flea infestation and the allergy
are the most important causes of itchiness in dogs. Practically all dogs
will have fleas at some time during their lives. The rump and hind end
are most often affected. Nibbling and itching gives a rough feel to the
coat and, if severe, pyotraumatic dermatitis (wet eczema) or alopecia
will result. Very importantly, dogs with atopic dermatitis are often
allergic to fleas as well, so it is pointless making a diagnosis of
atopy without taking rigorous flea-control measures. Similarly, other
parasitic infestations such as lice or sarcoptic mange may mimic atopy
and these should be carefully ruled out.
Food sensitivity (often called food allergy) is an uncommon cause of
allergic skin disease, which accounts for a small percentage of the
cases seen by dermatologists. Although a rare condition, all allergic
dogs should undergo food trials before being committed to long-term drug
therapy. Food sensitivity may coexist with atopy or flea allergy and so
partial responses may be seen to food changes. Bacterial infections are
a common cause of pruritis in the dog and these can be as a result of
atopic dermatitis or any other skin condition that damages the integrity
of the skin. Non-allergic causes of bacterial infection include hormonal
problems such as hypothyroidism and parasitic problems such as demodex
infestation. These are normally non-itchy conditions, but as soon as
there is bacterial involvement this changes and it can be difficult to
make the correct diagnosis.
Skin testing is performed to identify the allergens
involved in allergic disease. Under profound sedation an area of hair on
the chest is shaved and small injections of substances known to be
possible allergens made. After 15-20 minutes the reactions are recorded.
Figure 3 shows positive reaction to house dust mite allergens in
an allergic Labrador Retriever.
The diagnostic approach to the pruritic dog is summarized in figure
In treating atopic dermatitis it is imperative to consider
the situation as a whole. Bacterial infections will make the animal far
more itchy and may even contribute to worsening the allergy through
damaging the skins' protective mechanisms. So any bacterial infections
seen as a rash or pustular spots (Figure 5), need to be treated
promptly, using a combination of shampoos and antibiotics for a minimum
of three weeks, and often longer.
Corticosteroids medication is best withdrawn throughout the period of
treatment as steroids can interfere with the dogs ability to fight
infection. Natural products such as Essential Fatty Acid supplements
should be considered to supplement the diet.
Yeast infection (caused by the yeast Malassezia pachydermatis)
is another complication. Spots are not seen in this disease, but instead
the organism causes redness, greasiness and a mousy odour. Dogs can be
quite depressed when infected and can be extremely itchy. Treatment is
usually with baths containing enilconazole, or miconazole in combination
with Chlorhexidine. Tablet therapy is also available, but as a surface
infection Malassezia is best treated using baths. Supplementation with
Essential Fatty Acids is important to increase the dog's inherent
Similarly, fleas and other ectoparasites will make an atopic dog far
more itchy. All allergic animals should have regular and efficient flea
therapy using veterinary preparations to treat both the dog and the
environment. With bacterial, yeast and parasitic problems under control
most dogs will be very much more comfortable. This is a good time
to switch over to a nutritional supplement such as DERMATRIX.
A variety of drugs are now available for treatment. Generally they are
used in combination rather than alone. Their use is summarized in figure
Essential fatty acids (EFA) are now widely used for skin conditions.
They are known to have few side effects and will help about 25% of
allergic dogs significantly. DERMATRIX is a chewable EFA tablet that
also contains MSM, an important ingredient for skin conditioning, as
well as essential vitamins for skin health. Antihistamines potentiate
the action of essential fatty acids (synergy) and so combination therapy
would appear to be valuable. Several veterinary products are licensed
Antihistamines were widely dismissed as unhelpful in atopic disease
until recently when new studies both in the US and UK have shown
considerable benefits from their use. No veterinary products are
available and the human drugs, chlorpheniramine, hydroxyine, and
clemastine have all shown to be useful.
Steroids are widely thought to cause side effects which outweigh
their potential for good. Their use should be limited to only the most
severe cases of atopic dermatitis and should be discontinued as early as
Hyposensitizing vaccines ( also known as desensitizing vaccines) are
prepared from the allergens identified as important at skin test. By
administering these allergens subcutaneously over a long period the
immune response to them is modified and pruritis is reduced. They are
seen to be beneficial in about 60% of dogs, and take up to nine months
to have effect.
Allergen avoidance is useful when house dust mites are known to be
the problem. Exposure to bedrooms should be avoided by house dust mite
allergenic patients to minimize exposure to the allergen. When pollens
and moulds are involved avoidance is practically impossible as these
allergens travel for miles on the wind, although obviously very large
sources of pollens, for instance hay meadows for grass sensitive
individuals should be avoided.
Studies examining the incidence of atopy in the families where the dam
and sire have pruritic skin disease have shown that around 60% of their
offspring will have signs of allergic disease. When two unaffected
animals are bred the incidence is reduced to 10% and it would appear
possible to reduce the incidence of atopy within a breeding program by
avoiding those dogs with atopic disease. However identification of the
mildly-affected atopic dog can be difficult because we lack a definitive
test for the disease. Further studies to better predict which dogs will
develop atopy are ongoing and if useful information is forthcoming then
there is hope that we can reduce the incidence of this distressing
This article was contributed by Stephen Shaw, a Dermatology
Research Fellow at the Animal Health Trust.