I recommend taking your dog to your veterinarian for examination and treatment. The most common reasons for itchy skin in dogs include skin infections, microscopic skin parasites such as fleas, scabies or demodex mites, food allergy, or pollen/dust allergies. Dogs with fleas or allergies commonly scratch and traumatize themselves, creating secondary bacterial skin infections/rash and hotspots that make the itch worse. From your description, your dog likely has infected hotspots, which is something that needs veterinary care. If skin infection is present, it is treated with antibiotics for 3-4 weeks and mild antibacterial shampoos. Although Frontline is a good flea preventative, it would be worth trial treating your dog for scabies with Revolution; this product kills fleas as well as the hard to find microcopic skin mites that can mimic allergies. The itch can be treated symptomatically with mild oatmeal shampoos, fatty acids, antihistamines or a short course of oral steroids prescribed by your veterinarian, but steroids are not a good choice for long term treatment due to their many side effects. If your dog's itch persists or recurs despite antibiotics, parasite control and symptomatic medications, then I would suggest talking to your veterinarian about a prescription hypoallergenic diet. There is no accurate skin or blood test for food allergy; the test and the treatment are the strict hypoallergenic diet trial for 6-8 weeks with no other treats or foods. Lastly, if your dogs' symptoms persist despite all of the above, or if the symptoms only occur during certain seasons, then talk to your veterinarian about referral to a veterinary dermatologist for possible allergy skin testing and desensitization injections for pollen/dust allergies to identify and treat the underlying cause of the itch and recurrent infections, rather than just treating symptoms with medications (veterinary dermatologists can be found in your area by going to www.acvd.org and clicking on the "find a dermatologist" button). Hope that helps!
Kimberly Coyner, DVM
Diplomate, American College of Veterinary Dermatology