There are many types of allergies. Some only affect the skin, while others may also affect other parts of the body, such as the intestines, throat or lungs. Skin allergies typically start with itching. Certain parts of the body have more nerves which detect itching, so symptoms start there – the paws, ears, face, throat and in-between the legs.

Usually the skin is initially normal but later changes occur – thickening and discolouration of affected areas, increased oil secretions and hair loss. The skin is also less resistant to secondary infections – spots, crusts and raised inflamed areas develop. Hot and humid conditions allow these infections to worsen quickly.

The typical skin allergy is caused by four main things:

1. Fleas: When fleas bite, they inject a small amount of saliva into the skin. Dogs can develop an allergic reaction to this saliva, which is much more severe and long lasting than a normal fleabite. Even one fleabite is enough to cause allergic dogs to be very itchy all over their bodies for days. The hot and humid environment and small flats are ideal for rapid breeding of fleas, and dogs with allergies need constant treatment of both themselves and their environment to prevent any fleabites.

2. Contact allergies: This is rare, but direct contact of certain materials with the skin may cause reactions – natural cloth, certain floor types, and even floor wax can be the cause. Usually symptoms will develop in exposed areas with little hair, the feet, the belly and the chin are most commonly affected. Symptoms are usually severe, and diagnosis can only be confirmed by trial exposure if one is suspicious - for instance, a small piece of the suspected cloth can be taped to bare skin and the skin assessed for reaction.

3. Food allergies: This is also less common than many people think, and in animals it is usually the protein source, although carbohydrates or additives may occasionally cause problems. Normally the problem develops in young dogs, which are fed the same diet for a long period. Remember changing brands of food may not solve the problem, as most commercial dog foods will use similar mixes of protein sources, e.g. chicken or lamb. In the short term symptoms can be relieved with drugs, but in the long term changing to a diet without the cause of the allergy is essential. Prescription diets are usually effective, but no commercial diets are suitable at present. Sometimes people become confused as their dog improves on a diet over time and think this proves the dog is allergic to the old diet. However, all allergies tend to increase and decrease slowly all the time, so often the improvement is coincidental. Also, many diets help alter the skin’s immune system, which is beneficial whatever the cause of the allergy. Food allergy can only be confirmed if the dog improves over a 6-week period, on an exclusion diet, and then worsens immediately when fed the original diet.

4. Atopy (Inhalation allergies): This is the most common cause of skin allergies. In Hong Kong, many breeds of dogs, including ShihTzus, Schnauzers and Golden Retrievers, are predisposed to develop Atopy. Dust particles are the cause, and the same dust types as cause asthma in people are usually involved. Since most dogs in Hong Kong are kept indoor most of the time, indoor dusts, especially the remains of dead House Dust mites, are usually involved. Pollens, fungal spores and other animals’ hair are other common causes. To develop an allergy the dog needs to be exposed in two ways – Firstly, the dog must breathe in the dust containing the offending particle. Then these same particles need to be present on the skin surface. This triggers the immune system and chemicals released into the skin cause itching, and eventually other changes, which predispose to secondary infections and other complications. Most dogs that develop allergies are most likely, in time, to develop allergies to many different particles, and possibly food sources and fleas as well.

Allergies cannot be cured only controlled. Where possible, the cause of the allergy should be removed. While this is possible for flea and food allergies, it is much more difficult in dust allergies.

To find the cause is difficult. At present only one method is possible, which is intradermal testing. An area of skin is clipped and the skin injected with a tiny amount of the possible dust dissolved in liquid. This area is then assessed for reaction. At present we test for about 30 different dust types, but cannot obviously test for all possible causes, only the most common.

Blood tests have also been advertised or used by vets to try to find the cause of allergies. It is important not to be mislead by these tests – blood tests cannot diagnose allergies or their source. The blood tests can only give an indication of what the dog is exposed to, so a dog living in an old flat with old carpets is likely to test positive for house dust mites, whether allergic or not. A dog on a lamb diet will probably test positive for lamb, but negative for beef or other proteins.

If the source of the allergy is found, we can attempt to desensitize the dog. This involves injecting the dog with a vaccine made of the cause of the allergy. This ‘overstimulates’ the immune system, so that it starts to ignore the cause. This is only successful in 60-70% of cases. If the injections are stopped, the allergy will almost always come back again, so treatment is usually permanent.

Special diets, especially when combined with oils high in certain Omega-3 oils (such as Evening Primrose oil), are also effective in altering the skin’s immune system and reducing and controlling the allergy. This is our main recommended course of action for long-term treatment.

Frequent washing with soap-free shampoos will remove dust particles from the skin, reducing the allergy. All dogs with skin allergies should be on flea prevention treatments.

For dogs that need immediate relief or have secondary infections, drugs are necessary. Cortisone is the most common, and most effective treatment, but the side-effects of high doses or long courses mean that we usually use lower doses in combination with anti-histamines or other drugs which can reduce over-activity of the immune system. New drugs have recently become available which are safer and very effective. However, as they are still very expensive, they probably only need to be used on dogs where other treatments have been ineffective.

In summary, for all allergies there is no permanent treatment. Since most cases will resolve quickly with drug treatment, this is useful, but long-term control is very important. All allergies will periodically worsen and improve, and drugs should only be necessary during the worst periods, to prevent drug-induced side-effects