In one sentence, describe what the following article is about:

If you notice your dog scratching his irritated or sensitive skin, or if his ears and skin are greasy and smelly, take your dog to the vet. The veterinarian will check for causes of itchiness and irritation, such as parasites, and may suggest testing for environmental allergens or putting the dog on a trial elimination diet. Allergies are usually caused by the proteins in your dog's food, although common causes are beef, chicken, dairy, wheat, corn and soy. These also happen to be the most common ingredients that make up commercial dog foods. Preservatives and filler ingredients can also irritate your dog's digestion. Since so many ingredients, fillers, and preservatives make up commercial dog food, the vet will probably recommend a food elimination trial. To do this, you'll choose a food sensitivity diet to exclusively feed your dog. Avoid feeding any foods that aren't part of the chosen diet. This will help you determine what substance is bothering your dog. Remember not to feed treats or rawhide bones during the elimination diet. While this may seem harsh, it will take up to 6 weeks for your dog's body to “clear” the offending allergens from the body. Any other food during this time could potentially cause the diet to fail. When you're ready to closely monitor a strict diet for your dog, you'll need to select a food sensitivity diet. This way, you know exactly what your dog is eating. After several weeks, you should notice an improvement in your dog's allergies or you may realize that something in that particular diet is causing the problem. Some food sensitivity diets to try include:  Novel protein: With this diet, you'll choose a single source of a non-typical meat that your dog has never had before. This might include salmon, venison, buffalo, or duck, but only give your dog 1 of these proteins, not all 3. Since your dog hasn't been exposed to the protein, there's less of a chance that he's developed an allergy to it. Hydrolyzed protein: This diet is made up of proteins that are broken down into small component amino acids (which make up the protein). Since they're so small, your dog's body shouldn't notice the protein, preventing an allergic reaction.  Therapeutic: These diets which use a novel or hydrolyzed protein are made with higher levels of omega-3 and omega-6 fatty acids which can reduce the symptoms of food allergies. Once you and your veterinarian have determined the cause of your dog's allergies, choose a nutritious diet. The vet may recommend purchasing a specific commercial product or may prescribe a detailed diet for you to make for your dog. If you do decide to make your own food, you'll need to consult a certified nutritionist or dietitian who has spoken to your vet about your dog's dietary needs. A specialized diet is important for your dog since dogs have different mineral and vitamin requirements than humans. Most dogs do well on a diet made up of 40 percent meat, 50 percent vegetables and 10 percent carbohydrates.

Summary:
Have your dog examined for a food allergy. Consider an elimination diet. Choose a food sensitivity diet to try. Work with the veterinarian to create a balanced diet.