Of course it is normal for dogs to scratch, but a sudden and intense bout can be a sign of an allergic reaction. As such, it is important you determine why the dog is scratching, especially if the behavior is repetitive, prolonged, or intense in nature.
What To Watch For
A sudden, intense bout of scratching, especially for a prolonged period of time or during nighttime hours when sleeping should naturally take precedence. This may manifest as itching, biting, licking, and/or chewing of one or more parts of the body (also known as "pruritus").
Allergies, mites, skin infections, and minor insect bites are the most common causes of intense scratching.
Note: Uncontrolled scratching can lead to self-inflicted injuries or, rarely, in the case of some allergic reactions, to anaphylactic shock.
Restrain the dog.
Check the skin, especially in the itchiest areas.
If you can identify the cause of the itching -- as with insects or spiders -- remove it.
Apply cold compresses to the itchiest areas for about 15 minutes.
Oatmeal shampoos may be of some temporary relief in many cases.
If the dog’s scratching is intense, administer an antihistamine (call your veterinarian for the correct dose).
If the scratching continues, gets worse or has no apparent cause, take the dog to the veterinarian for a full physical exam and basic laboratory testing.
Diagnosis invariably involves skin scrapes, impression smears, ear swabs, and other basic methods to analyze the skin and its potential parasites/infectious agents. Response to treatment with certain products/drug is another helpful resource that may prove necessary. Allergy testing through food trials and blood or skin tests may be necessary as well.
The treatment for scratching, itching, chewing, licking, biting (also known as pruritus) requires an initial diagnosis. Only then can the approach to treatment be determined. Treatment may include anything from shampoos, dips, and cream rinses to antibiotics, antifungals, parisitacides, and immunosuppressants (like corticosteroids and cysclosporine). Food restriction and hyposensitization protocols may also be in order (as for food and environmental allergies, respectively).
Fleas and some mites may be prevented with a variety of over-the-counter and prescription medications. Ask your veterinarian for a product and/or drug recommendation. Otherwise, allergies have no specific means of prevention.