Pet Itching & Skin Rashes: Allergies, Parasites & What Your Vet Looks For

Skin disease is probably what we manage most chronically at this clinic. A dog scratching constantly could have fleas, a food allergy, a mite infestation, or a fungal infection. Each one requires a completely different treatment. Grabbing something off the shelf delays the right diagnosis and often allows secondary infections to develop that sit on top of the original problem and make it harder to sort out.

Why skin problems don't just resolve on their own

By the time most owners bring a pet in, the itching has been going on "for a while." And by then the pet has usually scratched and licked itself into a secondary bacterial infection that now sits on top of whatever originally started it. That layering is what makes skin cases take more than one visit to resolve. We are not going to keep treating the surface problem without identifying what's underneath it. Treating the infection without addressing what drove it leads to recurrence within weeks. Every time.

Environmental allergies — atopic dermatitis

One of the most common dermatological diagnoses we make in dogs, and we see it in cats too. The immune system overreacts to environmental allergens — pollens, dust mites, mold spores. In the San Gabriel Valley, multiple pollen seasons overlap year-round. There is no real "off season" for allergies here, which is why so many families manage this as a chronic issue rather than a once-a-year flare.

In dogs, atopy typically causes recurrent itching of the paws (licking, chewing), ears, face, belly, and armpits. Skin in those areas gets red, thickened, or darkened from chronic self-trauma. Ear infections in dogs with allergies are almost always a symptom of the underlying allergy — not a standalone problem you treat separately and never revisit.

Cats look different. Miliary dermatitis (small crusted bumps along the back), symmetrical hair loss from over-grooming, eosinophilic plaques on the belly. Cats groom at night and out of sight — owners notice the hair loss but don't realize the cat is causing it.

There's no cure for atopy — but allergen immunotherapy, veterinary anti-itch medications, medicated shampoos, and omega-3 supplementation make a real difference in daily comfort. Well-managed atopy isn't something the pet has to suffer through.

Food allergies

Real, but also one of the most over-suspected diagnoses in veterinary dermatology. A true food allergy is an immune-mediated reaction to a dietary protein — usually beef, chicken, dairy, or wheat, though any protein can be the culprit. The distinguishing feature: symptoms don't follow a seasonal pattern. Year-round itching around the face, ears, paws, and perianal area — sometimes with concurrent loose stool. That profile is worth investigating.

The only reliable diagnostic is a strict elimination diet trial: 8–12 weeks on a novel protein or hydrolyzed diet, with absolutely nothing else. No treats, no flavored medications, no dental chews. Blood and skin allergy tests for food exist but their accuracy in veterinary medicine is poor. We don't rely on them. The elimination trial — followed by reintroduction of the original diet to confirm recurrence — is still the gold standard.

Parasites — fleas, sarcoptic mange, demodex

Flea allergy dermatitis is the most common skin condition we see in Southern California. Fleas survive year-round in warm temperatures, and flea allergy isn't caused by fleas themselves — it's a reaction to flea saliva. In an allergic dog, a single bite triggers days of intense itching. Classic pattern: itching and hair loss at the base of the tail, lower back, and inner thighs, sometimes with hot spots developing. You may never see a live flea because allergic animals groom them off aggressively. Look for flea dirt — dark pepper-like specks that turn red on wet white paper. Treatment is year-round flea control on every pet in the household. One untreated pet reinfests the whole house. Over-the-counter products vary widely in efficacy — prescription preventives are worth using.

Sarcoptic mange is caused by Sarcoptes scabiei burrowing into the skin. The itch is intense and relentless in a way owners describe as unlike anything they've seen in their pet — focused on the ear margins, elbows, hocks, and belly. Highly contagious to other dogs; humans can get a temporary self-limiting rash. Skin scrapings are often negative even in active infections — we frequently treat empirically based on the clinical picture, and a treatment response confirms the diagnosis.

Demodex mites live in small numbers in hair follicles of all normal dogs. They only cause disease when immune function is compromised. Localized demodicosis — patchy hair loss around the eyes and muzzle — is common in puppies and often resolves on its own. Generalized demodicosis covers larger areas and in adult dogs warrants investigation for an underlying immune-suppressing cause.

Other things we see often

Ringworm — despite the name, it's a fungal infection, no worm involved. Circular, scaly patches with hair loss, sometimes with a slightly raised edge. Contagious to other animals and to humans. Fungal culture or Wood's lamp exam for diagnosis. Topical antifungals and sometimes systemic treatment for widespread cases. Housemates should be checked.

Foxtails — worth a specific mention for our area. Wild barley awns that embed in paws, ears, nostrils, and skin from spring through early summer. They drill inward and keep going. A sudden lump or draining tract on a pet with outdoor access should be examined promptly.

How we work through a skin case

Flea comb first. Every time. If there's any sign of fleas, we treat immediately — you can't reliably evaluate for food allergy in a flea-allergic animal because flea allergy dermatitis confounds everything else. Skin cytology identifies yeast and bacterial infections quickly. Skin scrapings look for mites. Fungal culture rules out ringworm. For complicated or recurrent cases, allergy testing and dietary trials are the next layer.

Bloodwork isn't usually the starting point for skin disease — unless we're looking for hormonal causes like hypothyroidism or Cushing's in older pets. Those drive secondary skin problems in ways that don't resolve until the underlying condition is managed.

Frequently Asked Questions