Many conditions cause itching to dogs that result to frequent scratching and biting of the affected area. Persistent itching is a very common sign of dog dermatitis. Some of the causes include:

~food allergies, drug reactions and exposure to toxins
~bacterial, fungal or yeast infection
~insect bites (flea saliva is an allergen) or parasitic infection
~breed-specific predisposition
~sunburn or contact with an irritating substance
~nutritional deficiencies

Although injectable corticosteroids can help calm the itching and inflammation, there are other safer and more natural approaches that may be more suitable such as natural food supplements and topical treatments.