Found a new lump on your dog? Here’s what it means and costs

You’re patting your dog and your fingers snag on something that wasn’t there last week. Most lumps aren’t cancer, but you can’t tell that from the couch. Late spring and summer also bring a rise in grass-seed injuries, which Pet Insurance Australia says shows up in its claims every year (Pet Insurance Australia), because dogs are out in longer grass, chasing balls through paddocks and picking up grass seeds that can turn into nasty abscesses. Here’s what’s actually going on under your dog’s skin, and what it might cost to find out.

What owners usually find first

Lumps get noticed in a handful of ways. Sometimes it’s a visible swelling. Sometimes it’s a spot that’s suddenly wet or smelly. Sometimes your dog won’t stop licking one paw or one spot on their side, and that’s what leads you to the lump, not the other way around.

• A firm, round lump under the skin that moves freely when pushed
• A soft, fluid-filled swelling, sometimes warm to touch
• A red, angry lump with a small hole oozing pus or blood
• A raised, dark or pigmented growth on the skin surface
• A lump between the toes, often with limping
• Sudden swelling on the face or muzzle

Location matters. Lumps between the toes, around the ears, or under the collar line in spring are far more likely to be grass seed related than lumps that have been slowly growing on the trunk or legs for months.

Grass seed abscesses versus tumours

These two get mixed up constantly because both start as “a lump appeared.” The history and the speed of change usually tell them apart.

Grass seed abscesses

Grass seeds (from barley grass, spear grass and similar) have a barbed shape that lets them burrow into skin but not come back out. Once inside they keep migrating, and the body reacts with inflammation and often infection or an abscess (Pet Insurance Australia). Common signs:

• Appears within a day or two, often after a walk in long grass
• Hot, painful, sometimes with a visible small entry wound
• Frequently between the toes, in the armpit, groin, ears or nostrils
• Dog is often chewing, licking or sneezing at the area
• May burst and discharge pus, then reduce, then flare again if the seed is still inside

Tumours

Most skin tumours in dogs are benign (MSD Veterinary Manual). Tumours, benign or malignant, usually behave differently from abscesses:

• Grows slowly over weeks to months (though some, like mast cell tumours, can change size overnight)
• Often not painful when first found
• Doesn’t come and go the way an abscess does
• More common in older dogs, though young dogs get them too
• Breeds including Boxers, Pugs, bulldogs, Golden Retrievers and Labradors are more prone to mast cell tumours (VCA Animal Hospitals)

The catch is that mast cell tumours can look like an insect bite, wart or allergic reaction, and can swell or change size suddenly (VCA Animal Hospitals), and some abscesses feel firm enough to worry you unnecessarily. You genuinely cannot tell by eye alone in a lot of cases. That’s not a cop-out, it’s just how skin lumps work.

How vets actually work it out

A vet doesn’t guess. There’s a fairly standard process, and it’s worth knowing what to expect so a routine visit doesn’t feel alarming.

Step 1: history and physical exam

The vet will ask when you noticed it, whether it’s changed size, and whether your dog has been off lead in grassland recently. They’ll check your dog’s temperature (normal for dogs is about 37.5 to 39.2°C, according to the Merck Veterinary Manual) because a fever points towards infection rather than a tumour.

Step 2: fine needle aspirate (FNA)

This is the standard first test (MSD Veterinary Manual). A small needle is inserted into the lump and cells are drawn out onto a slide, no sedation needed in most cases. It takes seconds, but it is usually charged on top of the consult, so ask your clinic for the price when you book. The vet can often look at it under the microscope in-house or send it to an external pathology lab for a definitive read.

Step 3: pathology or biopsy

If the FNA is inconclusive, or shows something concerning, the next step is a biopsy (removing part or all of the lump under sedation or general anaesthetic) and sending the tissue to a lab such as IDEXX or Vetnostics. Turnaround is usually 3 to 7 business days. This adds anaesthetic and surgical costs on top of the lab fee.

Step 4: imaging if needed

For lumps that might involve deeper structures, or if cancer is suspected and the vet wants to check whether it has spread, an ultrasound or x-ray may be recommended. This is more common with lumps on the trunk near organs, or in older dogs with a known tumour history.

What it costs

Costs vary by state and by clinic, so treat these as rough guide figures only and ask your clinic for a written estimate.

Prices are indicative ranges from the sources linked above (checked October 2026) and vary by clinic, location and your pet’s size and condition.

If a lump turns out to be a mast cell tumour or another malignant growth, ongoing costs (further surgery, oncology referral, chemotherapy) can run into several thousand dollars: Knose puts typical cancer or tumour treatment at $2,000 to $4,000, with severe cases reaching $30,000. If your dog is insured, check whether the policy covers pre-existing conditions and lump-related claims before you assume it’s covered, older lumps noted at a prior vet visit are sometimes excluded.

What you can check at home first

You don’t need to panic before the vet visit, but a bit of information helps the appointment go faster.

• Note the exact date you first noticed it
• Take a photo with something for scale, like a coin next to it
• Check if it’s painful (does your dog flinch or pull away when you touch it)
• Note whether it’s grown, shrunk, or stayed the same
• Check for a small hole or discharge, which points towards a foreign body like a grass seed
• Feel whether it moves freely under the skin or feels fixed to deeper tissue

Do not try to squeeze, lance or dig at a lump yourself. Grass seeds sit deeper than they look and squeezing can push infection further into the tissue.

When to call a vet

Any new lump on a dog should be checked by a vet, because the only reliable way to tell an abscess from a tumour is testing, not looking. That said, some situations need attention sooner rather than “book in next week.”

• The lump appeared suddenly and is red, hot or clearly painful, get seen within 24 to 48 hours
• Your dog has a fever (temperature above 39.2°C), is lethargic, or has gone off food
• The lump is between the toes and your dog is limping
• There’s an open wound, discharge, or a bad smell coming from the area
• The lump is growing quickly, changing colour, or has changed size within hours
• Your dog is repeatedly licking or biting at one spot
• Any lump on an older dog (over 8 years) should be checked promptly, since age raises the odds of it being significant

A lump that’s small, painless and unchanged for a week can usually wait for a routine appointment, but it should still go on the list. Skin lumps can have several causes, from harmless fatty deposits to infections to tumours, and there’s no shortcut around a physical exam and, in most cases, a needle test to know which one you’re dealing with.

Related reading

• Grass Seeds in Dogs: The Spring Hazard Aussie Owners Should Check For Now
• Why your dog won’t stop licking its paws this spring
• Why spring is prime time for ear infections in dogs and cats