The other part of any allergy is the way the body reacts to it. The reaction of the body is decided to a large extent by where the irritant is. In effect, this means that if the allergy is through contaminated food the dog could have a bad attack of gastroenteritis or food poisoning. Soapy water can enter the eye if you are giving the dog a bath, and the reaction is immediate redness. This is not a cause of worry, as the allergic reaction should subside shortly.
Similar allergens can produce different reactions in different animals.
It is based primarily on the type of climate that the dog is used to as well as the age of the pet. Thus dust in the house can result in causing a cold in some dogs whereas others might develop a breathing problem. Though other symptoms can also occur, this is a typical picture. Dogs can also be allergic to natural substances like herbs. An allergic dog will scratch, have skin rashes and runny eyes, sinusitis or bouts of cough.