What are allergies?
An allergy is an abnormal immune reaction to an otherwise harmless substance (an "allergen"). Allergies are one of the most common causes of skin disease seen in dogs.
What causes them?
Your dog's immune system is a very powerful, very effective defence mechanism - anything that gets into them that it doesn't recognise is attacked and destroyed. However, sometimes the immune system can make a mistake, and respond to a harmless substance in the environment (such as pollen, or a particular type of food, for example). Of course, this cannot be destroyed but the immune system tries really hard to do so! The most common allergen in dogs is thought to be flea saliva (nasty, but not actually harmful!), but they can respond to a wide range of other substances, such as pollen, certain types of protein found in food, storage mites, cleaning products, fabric softener and many more.
What dogs are at risk?
Any dog may develop an allergy; however, it is most common for dogs to become allergic early in adult life. It's important to remember, too, that a dog cannot become allergic to a substance until they have been exposed to it on at least two occasions.
What are the symptoms?
The exact symptoms will depend on what part of the immune system has been stimulated; in general, however, most allergies in dogs present with skin symptoms (yes, even food allergies). These include itching, reddening of the skin, hair loss, self-trauma (from the scratching) and secondary infections. In many cases, the skin first affected is that lining the outer ear canals, so dogs with allergic skin disease may initially appear to have an ear infection; the softer skin between the pads on their feet is also commonly affected (when this is involved, we call it "pododermatitis"). In other cases, the allergy may cause a runny, itchy nose ("allergic rhinitis", very like hayfever in humans!), itchy, sore eyes (allergic conjunctivitis) and, rarely, stomach upsets (especially diarrhoea).
How are they diagnosed?
There are three approaches to diagnosis. The first is to look at the history - when do the symptoms appear, are they associated with any type of food, or bedding, or environment? Do they only appear after walking under certain trees in the park, or if you've used a particular fabric conditioner? This will often allow us to determine what types of things are causing the allergy, but not always. If not, we can use special tests such as the IgE Blood Test (to look for raised levels of antibody in the bloodstream) or the Intradermal Allergen Test (where we inject certain substances into the skin and then measure the response). These both have strengths and weaknesses, but using a combination of the two we can usually determine the cause of your dog's allergic reactions. The exception is food allergies, as there are no lab tests that can diagnose the condition. In the case of a food allergy, the only way to demonstrate it is to put the dog on an Exclusion Diet, where they eat only either novel foods (that their immune systems have never been exposed to before) or, better, a hydrolysed diet (which is specially formulated so the immune system cannot respond to it). If the symptoms resolve, then we reintroduce one foodstuff at a time until we discover which one is the problem!
How can they be treated or managed?
The ideal treatment for any allergy is simple - avoid the allergen! In some conditions (like Flea Allergic Dermatitis) this is very doable - it isn't easy but it is possible to eradicate fleas in your house. However, this isn't always practical, so there are other options. The first is medication - there are a range of different medications available to reduce itching and damp-down the immune system's abnormal response. Some are rarely successful (such as antihistamines), some have many side effects (like steroids) and some are very expensive (like ciclosporin), but careful and judicious use of medication can make all the difference to a dog's quality of life. Other possibilities include desensitisation, where we "teach" the immune system to ignore harmless allergens.
Can they be prevented?
No - predisposition to developing allergies is partly genetic, but it also depends on the environment. Unfortunately, at this time they cannot be prevented.