Skin & Allergies

Everyone Blames Allergies. Check the Parasites First.

When a dog scratches nonstop, most owners jump straight to allergies. Vets work an itch in a specific order, and it starts somewhere else. Here's the diagnostic sequence, and the newer drugs that changed relief.

By Dr. Nina Kohl, Veterinary Dentist

July 29, 2026 · 7 min read

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For some dogs, scratching stops being an occasional itch and becomes a full-time job. Every waking minute goes to chewing a paw, gnawing a flank, or dragging a side along the carpet. When owners land on my exam table with a dog like this, most of them have already decided it is allergies. Sometimes they are right. But “it’s allergies” is a conclusion, and a lot of dogs get there without anyone doing the ruling-out first. There is an order to working an itch, and jumping to the end of it is how dogs stay itchy for months.

Here is the sequence I actually use, roughly cheapest-and-most-common to most-involved. Follow it and you skip a lot of wasted time and money.

First, rule out the things crawling on the skin

Before anyone says the word “allergy,” the parasites have to be off the table, because they are common, they are treatable, and they mimic everything else.

Fleas and ticks. Obvious in theory, missed constantly in practice, because a dog can be miserable with very few fleas on board. Some dogs are allergic to flea saliva — a condition called flea-allergy dermatitis — and for those dogs a single bite sets off an outsized, burning itch. You may never see the flea. This is exactly why year-round flea and tick prevention is the first thing I check: not because every itchy dog has fleas, but because it is the one major cause you can eliminate with certainty and cheaply.

Mites. Less famous than fleas, and sneakier, because certain mites burrow into the skin rather than crawl on top of it, driving intense inflammation and itch. You cannot see them. A vet diagnoses them with a skin scraping under the microscope, and most infestations clear with anti-parasite treatment. This is a big reason a real exam beats guessing at home — mange does not announce itself.

“Owners walk in certain it’s allergies, and half the time the very first skin scraping or a proper flea check reroutes the whole plan,” says Dr. Nina Kohl, DVM. “Parasites are cheap to rule out and miserable to miss. I’d rather spend ten dollars confirming there are no mites than three months chasing a food allergy that was never the problem.”

Then the skin barrier itself

Skin infections. The skin is armor, and when that armor is damaged or the immune system is run down, bacteria or fungi can overgrow and create an infection that is itchy, smelly, and angry-looking — sometimes moist and oozing, sometimes dry and flaky. Most clear with the right cleaning and medication. But an infection is often a passenger, not the driver: if your dog keeps getting them, something underneath is letting them start, and that is worth chasing.

Dry skin. Notice more scratching when the weather turns cold? As indoor heating dries the air, it dries skin, dog skin included. This tends to be minor, and a humidifier plus a vet-recommended moisturizing shampoo often settles it. It is the mildest item on this list, which is exactly why it is worth confirming before you assume something bigger.

Only now do allergies enter

Allergies are real and common, and once parasites, mites, and infection are handled, they are frequently what is left. Dogs react to seasonal triggers like grass, tree pollens, and molds, and to non-seasonal ones like household cleaners, yard chemicals, and food. The catch is that pinning down the specific allergen usually takes trial and error, sometimes including allergy testing or a strict elimination diet for suspected food allergies. Treatment ranges from removing the trigger where you can, to antihistamines and anti-inflammatories, up to corticosteroids or immunotherapy for tougher cases. This is a longer road, which is another reason not to start here before the quick wins are ruled out.

And sometimes it’s the brain, not the skin

Occasionally the itch really is in the head. Stress, anxiety, boredom, and compulsive disorders can all show up as relentless licking, chewing, and scratching with no primary skin cause. Often, a solid routine with real exercise, mental enrichment, and one-on-one time takes the edge off. Other times it needs a vet or a trainer. Behavioral itch is a diagnosis of exclusion, though, so it sits near the end of the list for a reason: you earn it by ruling out the physical causes first.

How to help your vet help your dog

You do not have to diagnose anything, but sharp observation shortens the whole process. Before your visit, note: Is the scratching worse at certain times of day or seasons? Is it getting worse over time? Where exactly — and is there redness, flaking, or hair loss there? Are other pets, or you, itching too? Answers to those questions genuinely change what a vet reaches for first.

At the visit, expect a thorough exam and likely some samples — skin scrapings, impressions, sometimes a biopsy. With luck the fix is as simple as parasite prevention or a medicated bath. Sometimes it is a longer partnership involving allergy testing, an elimination diet, or behavior work. Either way, the fastest path runs through your vet, not through the internet.

What newer research adds

The relief side of this story has genuinely improved. For itch driven by allergic skin disease, dogs are no longer stuck choosing between steroids and older antihistamines. Two targeted options now anchor treatment: Cytopoint, an injectable monoclonal antibody that neutralizes a key itch signal, and oral JAK-inhibitor tablets that dial down the inflammation behind the itch. Apoquel (oclacitinib) was the first of those tablets, and in September 2024 the FDA approved a second, Zenrelia (ilunocitinib), a once-daily tablet shown in a head-to-head study to be at least as effective as Apoquel; more than half a million dogs have now been treated with it, and the FDA further updated its label in 2025 as more safety data came in.

None of these are a cure, and they do not replace finding the underlying trigger. But they mean a dog does not have to suffer through the diagnostic process, and they have made long-term allergic itch far more manageable than it was even a few years ago. If your dog is on an older, sedating antihistamine and still miserable, that conversation with your vet is worth having.