Probably the second most common skin condition I see in dogs (after flea-related problems) is allergic skin disease, or atopy. Dogs can develop an allergic reaction to any number of things in the environment, or, less commonly, to their food. Common indoor allergens include house dust mites, detergents and carpet cleaning products. Common outdoor allergens include grasses and pollens. Food allergens include beef, pork, dairy products and wheat. And of course fleas themselves can cause allergic skin disease in some unlucky dogs. An allergic reaction is caused when the immune system makes antibodies to common substances instead of to those which are “foreign” to it. The antibodies cause mast cells in the skin to release chemicals like histamine, which cause irritation and inflammation. The most common age for dogs to show the first signs of allergic skin disease is when they are young, usually 1-3 years old. Some breeds are more commonly affected than others, and the tendency seems to run in families. For this reason, and because it can be a very distressing condition, it is not advisable to breed from affected dogs. The signs of allergic skin disease can occur all over the dog, but usually are most obvious on the feet, the ears and the tummy. The affected areas will be red and itchy, and usually this leads to the dog licking or chewing at the area which does further damage. Areas which are licked a lot will become reddish-brown in colour due to staining by saliva. After a long time the skin will become thickened and more pigmented, so may be black in colour especially on the tummy. Surface infection will often be present and have to be treated first before the cause can be found. Diagnosing the problem is by a mixture of examination and tests. A full examination of the dog will be needed to see if the skin disease is part of a bigger problem, e.g. thyroid disease. Blood tests may be needed to rule out such problems. Then the skin will be examined in more detail. The appearance of the skin gives clues but is not usually enough on its own to find out the cause. In any itchy skin condition it is important to rule out fleas, mites and lice, by taking a skin scraping and a hair sample. This can also be used to look for fungal spores. Once infection has been treated and parasites have been ruled out or treated, allergic skin disease may be a chief suspect. Finding out what causes an allergy is not very easy. There may well be more than one trigger, and allergy may develop to a substance which the animal has been exposed to before without any problems. If food is suspected, a special diet based on very few food sources may be recommended, but any improvement may take some weeks to show so it is important not to give up too quickly and not to feed any additional tit-bits. If a skin condition is very seasonal, always flaring up in the summer months, it makes it more likely that the cause might be grasses or pollens. Finding out what substances cause an allergy can be done with skin tests or blood tests. Skin tests involve the injection of minute amounts of suspected allergens under the skin and is usually done under sedation. Blood test have to be sent to a laboratory specialising in these types of tests. All the most common causes of allergies can be checked to see if an individual reacts to them. This is most useful if the allergen is something which can be avoided or removed from the dog’s environment. If avoidance is not possible, or if many allergens are involved, then treatment will be needed for the whole of the dog’s life. Antihistamines can help to reduce the distressing itch. Food supplements containing essential fatty acids can also be useful. Medicated shampoos also improve general skin health. Some cases may need to be treated with steroids, which help control the inflammation and itch but do not tackle the cause. The disadvantage is the risk of serious side effects, so they must be used appropriately. Steroids can be very useful and very necessary in some cases but are not ideal for all or for long term use. Another frequently used drug is cyclosporine which is an immunomodulator. It is unlikely to cause serious side effects and can give good long term control. Some dogs suffer from diarrhoea and vomiting at first but this often stops as treatment continues. Desensitisation is a technique where a unique vaccine is created for an individual dog according to the allergens which were identified by blood testing. This vaccine is then injected monthly, starting with very small doses and building up to a regular monthly dose. This can also be very successful for some dogs but may take months to take effect. Allergic skin disease is a very unpleasant condition, causing painful and distressing itchiness and often needing lifelong treatment. Diagnosis and treatment are not easy and will take time, which can be frustrating for both dog and owner. The best treatment will vary from one dog to another, so a lot of patience may be needed.