It's important to remember that skin disease is almost always a secondary condition. In order to provide the dog relief, you need to fix the primary problem.
Once I've ruled out metabolic diseases, the first thing I always do is put some flea medication on the dog. Many people don't know that it only takes 1 flea for a dog to have a full-blown reaction. Flea saliva has more than 17 different allergens.
The next step is to change the pet's diet. Most dog foods contain beef in some form or another. It's also known that many dogs that react to beef will also react to venison. It's important to feed the dog a single protein source, so I try to steer people toward duck and potato, fish and potato or something exotic like ostrich or kangaroo. However, the best diet is a modified protein diet such as Hill's Z/D. It's also important to feed the dog only the new diet for a minimum of 8 weeks. If the dog gets anything else, it may make ruling out food allergy more difficult.
Finally, I try antihistamines. There are at least 5 different antihistamines that have been shown to be effective in the dog. Before you try any antihistamine in your dog you need to speak with your veterinarian. I will even add omega-3 fatty acids or fish oils to the mix in extreme cases.
This is about as far as most general practitioners can take a case. If these steps fail, the next step is a veterinary dermatologist. These specialists can test your dogs specific allergies and make a vaccine to help control your dog's allergy.
Many veterinarians will attempt to control itchy dogs with steroids. This is great for business. The dogs get better and the clients love the convenience. Remember, though, most skin diseases are secondary problems. Masking the signs of allergies doesn't fix the primary problem. Also, just like the antihistamines, the steroids will eventually fail. Plus, excessive steroid therapy has the added effect of leading to liver failure, urinary tract infections and stomach ulcers.