There are numerous things that will cause a dog to itch. The most common are fleas, dry skin, food hypersensitivity, and allergies. There are also many uncommon conditions that will cause dogs to itch such as mange mites, chemical burns, auto-immune diseases, ringworm, etc.
Every animal has an itch triangle.
The triangle is made up of the things that cause a dog or cat to itch. Each pet's triangle is composed of different combinations of the above causative agents. The first thing your veterinarian will do is to rule-out the common causes of itching. He or she will perform a thorough physical examination that may include skin scrapings, fungal cultures, impression smears, or looking at the skin through a magnifying lens. Many times shaving the hair from the affected sites will reveal the cause of the problem.