Itchy Spots That Start Like Flea Bites and Turn Into Pimples

What you describe, a red spot that becomes a pustule, pops and leaves a peeling ring that changes color, is the typical pattern of a superficial bacterial skin infection (pyoderma). In dogs it is almost always triggered by something underneath, most often an allergy. The impetigo you saw is one form, mostly seen on the belly of young dogs.

The key is to treat both the infection and the cause. Ask your vet about skin cytology to confirm bacteria, and a culture if the spots keep coming back, so the right antibiotic or medicated shampoo can be chosen. Then look for the trigger: strict flea control on every pet in the home, and a proper food trial or allergy work-up. A diet trial needs a single new protein or a prescription hydrolyzed diet with nothing else by mouth for at least 8 weeks, and fish is a common ingredient, so it may not be a new protein for him.

Antihistamines alone often don't help much. If the newer anti-itch medicine worked but cost was the problem, ask your vet about other options, including medicated bathing, which can reduce both itch and infection. See skin infections in dogs, staph infections in dogs and dog allergies.

This is general information, not a diagnosis. Please follow your own vet's advice.