Quick answer: The most common causes of excessive scratching in dogs are environmental allergies, food allergies, fleas, and dry skin — each with distinct patterns that help identify the right cause.
Even if you don't see fleas, flea allergy dermatitis causes intense scratching especially at the base of the tail, belly, and thighs. Check for flea dirt (black specks that turn red on wet paper towel). A single flea can cause significant scratching in allergic dogs — treat for fleas even if you're not sure.
Environmental allergies (pollen, dust mites, mold) tend to be seasonal or year-round and affect paws, face, belly, and armpits. Food allergies are usually year-round and often include digestive symptoms alongside skin issues. Both require vet diagnosis for effective long-term management.
Low humidity, over-bathing, or poor nutrition causes dry flaky skin and itching. Look for dandruff and a dull coat alongside scratching. Omega-3 fatty acid supplements and a higher-quality diet often improve dry skin noticeably within a few weeks.
Start with flea prevention even without seeing fleas — it's the easiest fix. If scratching continues after ruling out fleas, a vet visit to identify the allergy type is the next step.