Atopic Dermatitis

Definition | Causes | Symptoms | Diagnosis | Treatment | Pictures
This page contains a detailed discussion of atopy.
If you would prefer a briefer introduction refer to Novartis' brochure: An Introduction to Skin Allergies in Dogs

What is atopy?

Atopy, or atopic dermatitis, is an allergic skin disease that causes pruritus (itching). It is one of the two most common skin allergies in dogs and cats, along with fleas.


With atopy, the dog's immune system "overreacts" to foreign substances (allergens or antigens) in the environment. Typical allergens that cause atopy include pollens (from grasses, weeds and trees), dust mites and moulds. It was once thought that these allergens were inhaled (similar to asthma in people). It is now known that absorption of allergens through the skin is more important. Atopy is inherited, but it is a complex disease and its causes are not fully understood.

atopic dog


Pets with atopy will often itch all over, initially with no signs of any rash or skin lesions. Eventually, scratching, chewing and licking will cause redness, hair loss, dry flaky skin and a variety of other signs.

In dogs, the most commonly affected areas are the feet and legs, ears, face, armpits and underbelly. Affected dogs will lick their feet, scratch all over and sometimes rub their face on the ground. Saliva may stain white hair a reddish-brown colour, especially on the feet.

Often the first signs (and sometimes the only signs) occur in the ears. Redness in the ears or recurrent ear canal infections may be a sign of atopy.

Pictures of some of the symptoms of atopic dermatitis are shown at the bottom of this page.

Cats with atopy will commonly lick themselves, although their owner will not always see this. Typical signs include areas of hair loss or raw, inflamed skin lesions. Multiple small scabs over the body, and rubbing of the face, neck and ears may also be seen. Hair in the vomit or faeces may indicate excessive licking.

The first signs of atopy are usually seen between 1 and 3 years of age, though this is variable. Some puppies can show signs of atopy at 8-10weeks, and older dogs may also develop atopy, particularly if they have been introduced to a new environment in the last few years.

Infections often occur as a result of the constant biting and scratching, and make the problem much worse.

Atopy may be either seasonal or year-round. It is common for animals to be allergic to more than one thing, which can make diagnosis difficult. Atopy will usually get worse every year, and a seasonal allergy will often develop into a year-round problem.


There is no specific test for atopy. Diagnosis depends on careful consideration of all the presenting signs, and ruling out all other diseases that could be responsible. Other diseases that could cause pruritus include fleas, mites, bacterial and fungal infections, and food allergies.

Diagnosis will involve some or all of the following:

Some of these tests may need to be done more than once before a final diagnosis is made, or repeated later during the course of the disease.


It is important to realise that atopy is a condition that usually requires life-long management. There is usually no complete cure, but most cases can be successfully controlled. A number of different treatments may need to be tried, or used in combination before a successful result is found. Even then, treatment modifications over the life of the dog are to be expected.

It is also important to understand the concept of the "itching threshold". A certain number of allergens may be well tolerated by your dog, and cause no signs of disease. But a small increase in the allergen load, may be enough to push the dog 'over the edge'. Other factors such as some fleas or a mild infection, a change in the environment, stress or boredom, may be enough to initiate itching and other clinical signs. The good news out of this is that we don't need to cure all of your dog's allergies. We just need to keep things down to a level where they experience little or no discomfort from them.

There are numerous options available, and usually the best result will be achieved with a combination of treatments. A number of factors need to be considered, including seasonality, the amount of skin involved, risks and cost. We'll work with you in coming up with the most practical treatment plan for you and your pet.

If you have any other questions about managing your pet's atopy, please phone us or make an appointment.

Related articles:

Partial hair loss on the back of a dog's paw
Partial hair loss on the back of a dog's paw Lumps and pimples on the belly
Lumps and pimples on the belly
Redness inside the ear
Redness inside the ear