What Causes Warts on Dogs? (Canine Papillomavirus)

When to call the vet. Most warts are not emergencies, but some situations need prompt attention. Call your veterinarian the same day if a growth is bleeding and will not stop, sits on an eyelid and rubs the eye, or is on a paw and causing limping, and if your dog is squinting, pawing at the face, drooling heavily or struggling to eat because of growths in the mouth. Go to an emergency vet if your dog cannot eat or drink at all, is gagging, choking, breathing noisily or having trouble breathing, if bleeding is heavy or will not stop with gentle pressure, or if your dog is lethargic, feverish or collapsing. Any new lump should be checked by a vet, and only a needle sample or biopsy looked at under a microscope can tell you what it actually is.

Most true warts on dogs are caused by canine papillomavirus, a family of viruses that infects skin and mucous membrane cells and makes them multiply into a raised, rough growth. The virus spreads by direct contact with an infected dog or with something an infected dog touched, and it usually needs a small break in the skin to get in. Dogs with immature or suppressed immune systems are the most likely to develop visible growths. Plenty of other bumps that owners call warts are not viral at all, but ordinary age-related skin growths that look similar from a metre away.

That distinction matters, because the cause changes what happens next. Here is how to tell what you are actually looking at.

The virus behind true warts, and why it takes hold

The medical name for a wart on a dog is a papilloma, and the viral kind is a viral papilloma or, when there are many in the mouth, canine oral papillomatosis. Several distinct canine papillomaviruses have been identified, and different types favour different tissue: the lips and mouth, the eyelids, the skin of the body, the footpads, the spaces between the toes.

The virus is transmitted dog to dog. Nose-to-nose greetings, shared water bowls, shared toys, communal chews, grooming tables, boarding kennels and daycare floors are all plausible routes. Papillomavirus is a hardy, non-enveloped virus that can persist in the environment on objects, so a dog does not have to meet an infected dog directly to be exposed. Growths typically appear weeks to a couple of months after exposure rather than immediately, which is why the source of infection is often impossible to pin down.

Exposure alone is not enough. The immune system is the deciding factor, and that explains the two groups of dogs who get viral warts most often:

• Young dogs. Puppies and adolescents have an immune system still learning the catalogue of threats. Oral papillomatosis in a socially active young dog is a recognised, well-described pattern, and in otherwise healthy dogs the growths commonly regress on their own once immunity catches up.
• Dogs with suppressed immunity. Dogs on long-term immune-suppressing or steroid medication, and dogs with systemic illness, are more prone to papillomas and to papillomas that persist. If your dog is on any such medication, keep giving it as prescribed and raise the new growths with your veterinarian rather than changing anything yourself.

So when owners ask what causes warts on a dog's skin as opposed to the mouth, the short answer is the same virus family acting on a different tissue, usually where the skin is thin, damp or scraped: the muzzle, the eyelids, the groin, the armpits, between the toes.

What warts on dogs look like, site by site

People search for pictures of warts on dogs because the descriptions never quite match what is on the dog in front of them. A written description still gets you closer than a stock photo, because photos flatten texture and hide the detail that matters most.

A classic viral papilloma is a small, firm, raised growth with an irregular surface, often described as cauliflower-like, frond-like or like a tiny sea anemone. Colour ranges from pale pink to grey-white to the same shade as the surrounding skin. Size is usually modest, and they frequently appear in clusters rather than singly.

By location:

• Mouth, lips and gums. Pale, soft, cauliflower-textured clusters on the gums, inner lips, tongue or roof of the mouth. In a young dog, this is the textbook presentation. Heavy clusters can make eating messy or cause drooling and bad breath.
• Eyelid margins. Small stalked or frond-like growths on the lid edge. These can rub the surface of the eye, which is a reason to have them looked at promptly rather than waiting.
• Body skin. Firmer, drier, often darker growths that look more like a hard bump with a rough top than a cauliflower.
• Paws and between the toes. Firm, sometimes inward-growing lesions that can be sore to walk on and are easy to confuse with an interdigital cyst or a foreign body reaction.

The other half of the answer is that many lumps owners call warts are not papillomas. In middle-aged and older dogs especially, the most common wart-lookalike is a sebaceous adenoma: a benign growth of an oil gland that sits on the skin like a small pink cauliflower, bleeds when nicked by clippers, and has nothing to do with any virus. Skin tags, follicular cysts and histiocytomas round out the list.

Wart or something else? How the common lumps compare

Growth	Typical appearance	Typical age	Contagious to other dogs	Usual concern level
Viral papilloma	Cauliflower or frond-like, pale, often in clusters, mouth and face common	Young dogs, or any dog on immune-suppressing medication	Yes, dog to dog	Low in healthy dogs, but worth a vet exam
Sebaceous adenoma	Small pink or greasy cauliflower-like bump, often on the trunk or head, bleeds easily	Middle-aged to senior	No	Benign, monitor, remove if irritated
Skin tag	Soft, flattened or stalked flap of skin, smooth rather than rough	Any adult age	No	Benign, cosmetic
Histiocytoma	Raised, red, hairless button-shaped lump, appears fast	Young dogs	No	Usually benign, often self-limiting
Mast cell tumour	Highly variable, can mimic almost anything, may change size or redden	Any age, more often adult	No	Needs prompt veterinary diagnosis
Squamous cell carcinoma	Ulcerated, crusted or non-healing raised lesion, often on paws, nail beds or thinly haired skin	Older dogs	No	Needs prompt veterinary diagnosis

Any lump that bleeds, ulcerates, grows quickly, changes colour, bothers your dog or sits on the body for more than a few weeks deserves a veterinary look, because the only reliable way to separate a harmless wart from something serious is a sample under a microscope. A fine needle aspirate or a biopsy takes minutes in a consultation room and ends the guessing.

Are they dangerous, contagious or painful?

Are warts on dogs normal? Common, yes. Normal in the sense of expected in a young, social dog or an ageing dog with changing skin, also yes. Normal in the sense of ignorable, no. A growth is a finding, not a diagnosis.

Are warts on dogs dangerous? Most viral papillomas in healthy dogs are not. The complications that do occur are mechanical and secondary: a wart on an eyelid rubbing the cornea, a wart between the toes making a dog limp, a wart in the mouth getting chewed and infected, or a heavy cluster interfering with eating.

Can warts on dogs be cancerous? A true viral papilloma is a benign growth. The real risk is misidentification. Squamous cell carcinoma and mast cell tumours can both present as a raised, rough, wart-like lesion, and no owner, and no honest practitioner, can tell them apart by eye with certainty. Rarely, long-standing papillomas have been described as undergoing malignant transformation. Both facts point the same direction: get it sampled.

Can warts on dogs spread to humans? No. Papillomaviruses are highly species-specific, and canine papillomavirus is not considered a risk to people or to cats. Your dog can pass it to another dog. He cannot pass it to you.

Do warts on dogs itch or hurt? Many are neither itchy nor painful and the dog ignores them entirely. But warts in high-traffic locations do cause trouble: ones between the toes or on a pad can be painful to walk on, ones in the mouth can be sore if chewed, and any wart that gets licked, scratched, caught on a collar or nicked by clippers can become inflamed, infected and genuinely uncomfortable. Persistent licking or chewing at one spot is a reason to call the clinic, not a reason to wait.

What to watch at home, and what to tell your vet

A growth you can describe precisely is far easier for a veterinarian to work with than one you noticed at some point recently. Keep a simple record from the day you first see it.

Watch and note:

• Where it is. Lip, gum, eyelid margin, between which toes, left or right side. Map every growth you can find, not just the obvious one.
• How many there are, and whether new ones are appearing.
• Size and shape over time. Photograph each growth in good light beside a familiar object for scale, and repeat the photo on the same background at intervals so changes are obvious.
• Surface changes: bleeding, crusting, ulceration, colour change, a smell, discharge.
• Your dog's behaviour: licking or chewing at one spot, rubbing the face, squinting or watery eyes, limping or holding up a paw, dropping food, drooling, reluctance to chew, bad breath, weight loss, low energy.
• Background information your vet will ask for: your dog's age, any current medication, any recent illness, recent daycare, boarding, grooming or dog park visits, and whether other dogs in the household or social circle have similar growths.

What not to do at home: do not cut, pick, squeeze, burn, tie off or band a growth, and do not apply human wart treatments, essential oils or other home remedies. These can cause pain, bleeding and infection, and they can destroy the tissue a veterinarian needs for an accurate diagnosis. Keep nails trimmed so scratching does less damage, use a recovery collar if your dog keeps licking a spot, and tell your groomer where growths are so clippers do not catch them. While visible growths are present, it is sensible to avoid sharing bowls, toys and chews, and to let daycare or boarding staff know.

What happens next belongs to your veterinarian. Many viral papillomas in otherwise healthy young dogs regress as immunity develops, and results vary from dog to dog. If a growth persists, sits somewhere it causes damage, keeps getting traumatised or becomes infected, your vet may recommend sampling, removal or another approach, and your vet may prescribe medication. Surgical removal is often the standard of care for growths that cause problems, and that decision belongs to your vet or surgeon after examining your dog.

Treat it as an emergency, rather than a next-available appointment, if bleeding will not stop, if your dog cannot eat or drink, if breathing is noisy or laboured, if the eye is painful, cloudy or closed shut, or if your dog is dull, feverish or collapsing.

Key Takeaways

• True warts on dogs are papillomas caused by canine papillomavirus, spread by direct contact with infected dogs or contaminated objects, usually entering through a small break in the skin.
• Young dogs and dogs on immune-suppressing medication are the most susceptible, because immune status, not exposure alone, decides whether growths appear.
• Classic viral papillomas look like pale cauliflower-textured clusters, most often around the mouth, lips, eyelids, paws and thinly haired skin.
• Many wart-like lumps on older dogs are sebaceous adenomas or skin tags, which are not viral and not contagious.
• Canine papillomavirus does not infect humans or cats, but it does pass between dogs.
• Most papillomas are benign, but squamous cell carcinoma and mast cell tumours can mimic them, so any persistent, bleeding, fast-growing or bothersome lump needs sampling.
• Warts between the toes, on eyelids or in the mouth cause the most discomfort and the most complications.

Your veterinarian owns this: the examination, the aspirate or biopsy, the decision to remove a growth or monitor it, and the plan for any dog whose immune system is the underlying story. Nothing on this page replaces that. Nothing here treats, cures or prevents any condition; every decision about your dog's care belongs with your veterinarian.

Related guides: What Does It Mean If Your Dog Has Skin Tags? (Explained) and Why Is My Older Dog Getting Lumps? (What's Normal).