Dog Allergies: The Complete Guide — Part 1: Why Your Dog Won't Stop Itching & What's Really Going On

Rachelle Gosnell
5 hours ago
9 min read

Cocker Spaniel portrait Alt text: “Cocker Spaniel portrait for dog allergy awareness — Part 1 of the Dog Allergies Complete Guide by Hendricks and Maple, hendricksandmaple.com

A note from Rachelle

I’m not a vet. I’m a retired breeder and an everyday dog mum who researches obsessively and refuses to accept “just manage it” as a final answer. I went down this rabbit hole so you don’t have to.

If you’re reading this, your dog is probably still itching, still suffering, and you’ve probably already spent more money than you want to think about on vet visits, prescription medications and special shampoos — and it’s still not fixed. Maybe it got better for a while. Maybe it’s getting worse.

Here’s something important to understand about the medications commonly prescribed for allergies — Apoquel, Cytopoint, steroids: they are symptom management. They suppress the immune response that’s causing the itch, but they don’t address the reason the immune system is overreacting in the first place. And over time, they can become less effective — because the underlying cause is still there.

This four-part series is my deep dive into what is actually going on, what is actually causing it, and what you can actually do to fix it. Not manage it — fix it.

The information is detailed and comprehensive, with references at the end of each section, so you can understand exactly what is happening and feel genuinely empowered to help your dog heal — instead of feeling helpless.

The real causes are usually one or more of these: what your dog is eating, the chemicals going on their body or into their environment, a damaged gut that is no longer doing its job properly, or a broken-down skin barrier letting in everything it should be keeping out. All of these are addressable. Many of the solutions are cheaper than what you’re currently spending. Some of them are already in your kitchen.

I also want to say this clearly: dogs are being euthanased and surrendered to shelters because their owners have run out of money trying to manage this. That breaks my heart — and it doesn’t have to happen. There are answers. Not quick fixes, but real ones.

This research was done in June 2026. Products and research move on, so if you’re reading this later, it’s worth checking whether newer options are available — but the fundamentals here don’t change so you can always research any products to see if it meets the requirements needed to be beneficial.

Knowledge is power. Start here.

Nothing in this blog series constitutes veterinary advice. Always consult your vet before changing your dog’s treatment plan — especially for parasite prevention such as flea and tick medications, where stopping treatment without veterinary guidance can be dangerous or fatal.

This is Part 1 of 4 in our extensive deep-dive series: Dog Allergies: The Complete Guide. This topic is too important — and too often misunderstood — to cover in a single post.

Your dog is itching constantly. Ears red, paws chewed raw, belly rashy. You take them to the vet and walk out with a prescription for Apoquel — sometimes within minutes. No elimination diet. No discussion of gut health. No mention of what might actually be causing it.

Sound familiar?

Millions of dogs worldwide are living with chronic allergies. The standard veterinary approach addresses the symptoms with powerful drugs — but often not the underlying cause. Here’s what’s actually going on.

chocolate Labradoodle licking itchy paw from dog allergies — Part 1 of the Dog Allergies Complete Guide by Hendricks and Maple, hendricksandmaple.com

Dog Allergies: Does Any of This Sound Like Your Dog?

Dog allergies can show up very differently in different dogs — the same root cause can produce completely different symptoms. Run through this list. Recurring symptoms, even just one or two, are worth investigating.

On the skin: - Constant scratching, biting, licking, or rubbing against furniture - Red, inflamed patches — particularly on the belly, inner thighs, armpits, and around the face - Hair loss from over-scratching or over-grooming - Dandruff, dry or flaky skin - Hot spots — raw, wet, matted patches that appear quickly, often overnight - Yellow or honey-coloured crusting on the skin — this is pyoderma, a secondary bacterial skin infection that develops in the broken skin of a scratching dog. It is caused by Staphylococcus bacteria colonising the damaged skin surface and is one of the most commonly missed signs that an allergy has been going on, untreated, for too long.³⁰ - Skin darkening — brown, grey, or black patches, especially in the groin and armpits (chronic cases) - Leathery, thickened skin (long-term chronic inflammation) - A persistent musty or corn chip smell — not just from paws, but from the coat generally (yeast overgrowth — covered in detail in Part 2)

On the ears: - Recurring ear infections — treated, cleared, then back again - Head shaking, scratching at ears - Dark, waxy discharge with an unpleasant smell - Redness inside the ear flap

On the eyes: - Watery, red, or goopy eyes — discharge, weeping, or persistent wetness - Rubbing the face along the carpet or on furniture - Swollen or irritated tissue around the eyes - Tear staining (the reddish-brown staining below the inner eye corners)

On the paws: - Licking and chewing at the paws — particularly between the toes - Brown or rust-coloured staining between the toes (from saliva, a sign of chronic licking) - Inter-digital redness, swelling, or cysts - Sore, inflamed paw pads

Digestive symptoms: - Vomiting — particularly after meals, or after eating a specific type of food - Loose stools, diarrhoea, or mucus in the stool - Excessive flatulence - Gurgling stomach sounds - Grass eating (a common signal of nausea or gut discomfort)

Respiratory symptoms: - A dry, hacking cough — particularly triggered by exercise, excitement, or pulling on a collar - Wheezing or noisy breathing - Reverse sneezing (a rapid, repetitive snorting inhalation — alarming to witness, but often allergy-related) - Runny nose, nasal discharge - Snoring that is new or has worsened

These respiratory symptoms are recognised as allergic bronchitis in dogs — an overreaction of the airways to inhaled allergens such as pollen, dust mites, mould, and household aerosols. VCA Animal Hospitals specifically notes that synthetic laundry fragrances can trigger allergic bronchitis in dogs.³¹

Urinary symptoms: - Recurring urinary tract infections (UTIs) — treated with antibiotics, then returning - Accidents in a previously house-trained dog, without an obvious cause - Frequent urination

This one surprises most people. While the research on a direct dietary allergy-to-UTI pathway is still developing, veterinary nutritionists note that food sensitivities affect urinary pH, hydration status, and immune function — all of which influence susceptibility to UTI pathogens. When the dietary trigger is removed and the immune system is no longer under constant inflammatory load, some dogs see their UTI pattern resolve. The connection is real, even if the mechanism is not yet fully mapped.³¹

General wellbeing signs: - Lethargy or low energy during flare-up periods - Reduced appetite during flares - Seeming generally “off” or uncomfortable without an obvious reason

The critical thing to understand: one dog may scratch constantly and never have an ear infection; another may have recurring ear infections and perfect skin. The same root cause expresses differently in every dog — and that is exactly why it gets missed. If any of these recur after treatment, something underlying is driving them.

German Shepherd at vet consultation for dog skin allergies — Part 1 of the Dog Allergies Complete Guide by Hendricks and Maple, hendricksandmaple.com

The Drugs Your Vet Will Likely Reach For

There is now a whole category of prescription allergy drugs for dogs — and vets are reaching for them faster than ever. Here is what they are, what they actually do, and what they don’t tell you in the consult room. Your vet may also reach for corticosteroids (prednisone or prednisolone) for acute flare-ups — fast and effective short-term, but we cover what repeated steroid courses do to your dog’s gut in Part 2.

Apoquel (oclacitinib) — made by Zoetis

Apoquel is a JAK inhibitor — it works by blocking the immune signalling pathways that trigger itching and inflammation. It can provide fast relief and is widely prescribed. But here’s what the drug’s own clinical data shows:

Reported side effects include: - Vomiting, diarrhoea, and loss of appetite - New skin lumps (reported in 2.6% of trial dogs) - Lethargy - Increased susceptibility to bacterial and fungal infections - Demodicosis (mite overgrowth) due to immune suppression - Worsening of pre-existing tumours - Bone marrow suppression with long-term use - Neurological effects including seizures, particularly in dogs with pre-existing seizure conditions¹

Long-term use carries sustained immune suppression. The drug can stop working over time as the underlying cause remains unaddressed, and some dogs require escalating doses for the same effect.

Zenrelia (ilunocitinib) — made by Elanco

Zenrelia is the newer once-daily oral tablet in the same JAK inhibitor family as Apoquel. It is a non-selective JAK inhibitor, meaning it blocks a broader range of immune signalling pathways. Approved for dogs 12 months and older.

Reported side effects include: - Vomiting, diarrhoea, soft stools, and low appetite - Lethargy - Neutropenia (low white blood cell count) - Elevated liver enzymes - Fever - Abdominal discomfort - Coughing and wheezing - Increased susceptibility to infections due to immune suppression²

Numelvi (atinvicitinib) — made by Merck Animal Health

Numelvi is the newest entry in this category — FDA-approved and marketed as the “first and only second-generation JAK inhibitor” for dogs. It is more selective for JAK1 than its predecessors, which Merck claims results in a better safety profile. It has been available from spring 2026.

What the label and prescribing information disclose: - Increased susceptibility to opportunistic infections, including demodicosis and interdigital furunculosis (deep paw infections) - New benign and malignant neoplastic conditions (tumours) have been reported with JAK inhibitors as a drug class - Field safety has only been evaluated beyond 28 days in limited studies — the long-term picture is still being written³

All three — Apoquel, Zenrelia, and Numelvi — work by suppressing the immune response that causes itching. None of them address why the immune system is overreacting in the first place.

Cytopoint (lokivetmab) — made by Zoetis

Cytopoint is a monthly injection rather than a daily tablet — a monoclonal antibody that neutralises IL-31, the specific molecule that signals the brain to itch. It is more targeted than JAK inhibitors and generally has fewer systemic side effects. It works well for 60–75% of dogs.⁴

The concerns: - It does not work for all dogs - Some dogs develop antibodies against lokivetmab over time, reducing its effectiveness - Long-term safety data is still limited - Like the JAK inhibitors, it suppresses the symptom rather than resolving the cause

All four drugs have their place in acute or severe cases. The problem is when they become the only and permanent solution — because not one of them is fixing anything. They are turning down the alarm while the fire keeps burning.

What About Over-the-Counter Antihistamines?

Before the prescription drug conversation, many owners reach for the human medicine cabinet — Zyrtec (cetirizine), Claratyne or Claritin (loratadine), or Phenergan/Benadryl (diphenhydramine). Vets sometimes recommend these as a first step.

A few things worth knowing:

• They work for roughly 30% of atopic dogs. Antihistamines are more effective for immediate allergic reactions (like a bee sting response) than for chronic atopic dermatitis, where the immune cycle driving the itch is already well established. Don’t expect the same relief you’d see in a hay fever sufferer.

• Dosing is completely different from humans — and must be calculated by weight. Never assume a human dose is safe or sufficient.

• Critical warning: check every label for xylitol — and for ‘birch sugar’. Some human antihistamine syrup formulations — particularly liquid children’s versions — contain xylitol as a sweetener. Xylitol is acutely toxic to dogs, causing rapid hypoglycaemia, liver failure, and seizures that can be fatal within hours. Important: xylitol is increasingly being labelled on products as birch sugar, wood sugar, or birch bark sugar — it is the same compound, with identical toxicity. The Colorado State University Veterinary Teaching Hospital and the FDA both confirm that birch sugar and xylitol are the same substance and carry the same acute danger to dogs. This rebranding is a marketing decision, not a safety reclassification. Always read the full ingredient list before giving your dog any human medication — and if you see birch sugar on a label, treat it exactly as you would xylitol.

• They don’t address the root cause. Like the prescription drugs above, antihistamines suppress the symptom. The immune overreaction driving the itch continues underneath.

If you use antihistamines short-term while investigating root causes, discuss dosing with your vet for your dog’s specific weight and condition.

What’s Actually Behind Dog Allergies?

We’ve covered what the drugs do — and what they don’t do. The next question is the one most consult rooms don’t get to: why is your dog’s immune system overreacting in the first place?

That’s what Part 2 covers in detail — the gut connection, the skin barrier problem, stress as a hidden driver, environmental triggers, the flea medications nobody discusses, breed predispositions, contact allergies, yeast and ear infections, and how to get a proper diagnosis. It’s the piece that makes everything in Parts 3 and Part 4 make sense.

blue English Staffordshire Bull Terrier in full sploot on wooden floor — Part 1 of the Dog Allergies Complete Guide by Hendricks and Maple, hendricksandmaple.com

This is Part 1 of 4 in the Dog Allergies: The Complete Guide series.

▶ Continue reading: Part 2 of 4 — Dog Allergies: The Complete Guide — Part 2: What Is Actually Causing It? Gut, Skin Barrier & Hidden Triggers →

About the author

This series was written by Rachelle Gosnell, founder of Hendricks & Maple — dog lover, obsessive researcher, and owner of four labradoodles who inspire everything she does. For more information on the author see the end of Part 4.

This post is for educational purposes only and should never be followed over or in place of professional veterinary advice. Always consult your vet before making changes to your dog’s diet, supplements, medication, or treatment plan.