Allergies in dogs

If your dog seems to be really itchy, is constantly scratching him or herself, has a rash, or is losing fur, he or she may have allergies. Unlike humans who react to allergens with sneezing, running noses, and sinus symptoms, dogs usually react with skin allergies. In the allergic state, the dog's immune system overreacts to a foreign substance (the allergen or antigen) to which it is exposed. The most common way those ‘overreactions' are manifested is through the skin, and can involve into everything from itchy skin, a red bumpy rash, hot spots, fur loss, and/or a poor coat texture. Dogs themselves may react to an allergen by simple scratching or licking, or more seriously by biting, chewing, or gnawing at their skin merely because they are irritated or uncomfortable.
Unfortunately, skin and ear related symptoms are probably the most common problems seen by veterinarians in dogs today, and both can lead to infections. On a more positive note, there are various different forms of treatments available for dogs with allergies, but it is important to begin with a proper diagnosis. After all, the method of treatment will be dependent on the form of allergen; but finding out just what is irritating your dog can be a very time consuming process. It is of primary significance, however, to rule out other possible ailments, such as bacterial infections, ear infections, and even thyroid disease.
There are a wide variety of different substances that may be bothering your dog, and the following categorizes them to make them somewhat easier to discover and diagnose. For some dogs, however, it can be almost impossible to find the exact cause of disturbance, so do not become too disappointed if you cannot find the allergen responsible — many treatments are still available.
http://catillness.today.com/2008/08/25/dog-types