You're scratching your dog behind the ears or along the back and your fingers stop on something new: a small, round bump that wasn't there last month. Maybe it's white. Maybe it has a dark center like a blackhead.
There's a good chance it's what most people call a sebaceous cyst, a benign pocket of skin debris trapped in a blocked hair follicle. But "good chance" is the catch. Several other lumps, including some that need prompt treatment, look and feel the same, and no one can tell them apart by touch alone. So the plan is simple: don't squeeze it, and have your vet check it, usually with a quick needle sample.
What Is a Sebaceous Cyst on a Dog?
Your dog's skin is packed with tiny sebaceous glands. Each one opens into a hair follicle and releases sebum, the oily substance that keeps the skin supple and gives a healthy coat its shine.
A cyst is a closed sac under or within the skin, lined by its own layer of cells and filled with whatever those cells produce. When the opening of a hair follicle gets blocked, the follicle can swell into one of these sacs. The lining keeps shedding material into it, so the sac slowly fills.
The name is a little misleading, though. Most lumps nicknamed "sebaceous cysts" aren't really full of sebum. According to the Merck Veterinary Manual, the most common skin cyst in dogs is the infundibular follicular cyst (also called an epidermoid or epidermal inclusion cyst), which is "erroneously called" a sebaceous cyst. It's filled mainly with keratin, the same tough protein that makes up the outer layer of skin. So if your dog's lab report says "follicular cyst" or "keratin cyst", it's describing the same kind of bump.
Blackheads (comedones) are close relatives. They're plugged follicles with a wider opening at the surface, which is where the dark dot comes from. They're common on the chest and pressure points of lean, thin-coated dogs. If you're curious about the smaller version, see our guide on whether dogs can get pimples.
What Does a Sebaceous Cyst Look Like?
A typical one is:
- A single, round, raised bump in or just under the skin
- White, slightly blue, or dark at the center
- Smooth and usually movable when you gently push it
- Anywhere from a few millimeters to more than 5 centimeters (2 inches) across
The contents are thick and cheesy: gray, brown, yellowish or white. If a cyst bursts on its own, you may see that material ooze out, sometimes looking like cottage cheese. An infected cyst can turn red, sore and smelly. If the bump you found doesn't match this description, our photo guide to common dog skin problems covers other lumps and rashes.
They show up most often on the head, neck, trunk and upper legs, but they can appear anywhere, including the feet.
The Types of Canine Cysts
"Cyst" covers several different things. Your vet or the pathology lab may use one of these names:
- Follicular cysts (infundibular, epidermoid): The most common type in dogs. A plugged, dilated hair follicle filled with keratin.
- Sebaceous cysts: Cysts that form in and around the sebaceous glands. They can pick up a secondary bacterial infection.
- Apocrine cysts: Smooth, round, fluid-filled lumps from the sweat glands, often on the head. The fluid is usually clear.
- Dermoid cysts: Rare, and present from birth. They form along the midline of the back or head and contain fully formed hairs. Rhodesian Ridgebacks, Kerry Blue Terriers and Boxers are the breeds most often affected.
- False cysts: Fluid-filled pockets without a true lining. They usually follow trauma or bleeding into the tissue and are common on the flank.
Causes of Sebaceous Cysts on Dogs
The common thread is a blocked or damaged hair follicle. Things that can set that off include:
- Injury or pressure on the follicle, especially at pressure points like the elbows
- A blocked pore or follicle opening
- Sun damage
- Rubbing or other mechanical damage to the skin
- Inactive follicles in hairless breeds such as the Chinese Crested and Mexican Hairless Dog
Genetics plays a part, too. Boxers, Shih Tzus, Schnauzers and Basset Hounds are predisposed to follicular cysts, and young dogs sometimes get several on the head. Hairless breeds tend to keep forming new ones.
Once blocked, the follicle keeps producing material with nowhere to go, so the sac grows. A dog that has had one cyst may get others elsewhere later.
Should You Pop a Cyst on Your Dog?
No. Those pimple-popping videos make it look satisfying, but squeezing a cyst is one of the worst things you can do to it.
The Merck Veterinary Manual is direct about this: squeezing can push the keratin out of the sac and into the surrounding tissue. Your dog's body treats that keratin as a foreign substance, and the result can be severe inflammation, a far bigger, sorer problem than the quiet bump you started with.
Breaking the skin also lets bacteria from the skin surface, or from your fingers, into the wound. And you can't be sure it's a cyst in the first place. Some tumors, including mast cell tumors, can look just like one.
The same goes for lancing, draining, or trying home remedies. If a cyst bursts on its own, call your vet. They'll tell you what to do until they can see your dog.
Licking and chewing make things worse. Your vet may recommend an Elizabethan collar, the cone-shaped collar, to keep your dog's mouth away from the spot.
Cyst or Something Else?
This is why every new lump needs a vet visit. The Merck Veterinary Manual lists several common skin lumps in dogs that can look like a cyst, including:
- Sebaceous gland hyperplasia and adenomas: Benign oil gland growths, common in older dogs and often several at once.
- Lipomas: Soft, benign fatty lumps under the skin.
- Histiocytomas: Raised, often hairless lumps, mostly in young dogs. Usually benign.
- Mast cell tumors: A skin cancer that can look like almost anything, including a harmless lump. Merck notes that visual signs alone can't establish the diagnosis.
- Trichoepitheliomas: Hair follicle tumors that can form cyst-like lumps.
Veterinary oncologist Dr. Sue Ettinger put it bluntly in Today's Veterinary Practice: even an experienced cancer specialist can't look at or feel a mass and know what it is. Her "See Something, Do Something" rule is a useful yardstick: a lump the size of a pea (1 centimeter) that has been there for a month should be sampled with a needle or biopsied.
Identifying a Canine Sebaceous Cyst
At the appointment, point out every lump and bump you've found, not just the one that worried you. Your vet will ask when you first noticed it and whether it has changed, then examine and measure it so there's a baseline to compare against later.
From there, the usual steps are:
- Fine needle aspiration (FNA): Your vet slides a thin needle into the lump to collect cells and contents. The sample goes on a slide for cytology, a look at the cells under the microscope. Keratin and debris point toward a cyst. Merck notes that needle cytology can spare pets unnecessary surgery.
- Biopsy and histopathology: If the needle sample isn't clear, or the lump is coming off anyway, the tissue goes to a veterinary pathologist. This confirms exactly what it is, rules out cancer, and shows whether the whole cyst was removed.
Dog Sebaceous Cyst Treatment
Treatment depends on what the sample shows and how the cyst is behaving. Your vet will talk you through the options, which may include:
- Watching it. Once a cyst is confirmed and it isn't bothering your dog, your vet may suggest measuring it and rechecking it rather than removing it.
- Surgical removal. Merck calls excision the treatment of choice for these cysts. Taking out the entire sac, lining included, usually cures that cyst. Leave lining behind and it can refill.
- Laser removal, an option for some cysts depending on their type and number.
- Treating infection or inflammation. An infected or ruptured cyst may need medication your vet prescribes, such as antibiotics.
Cysts that develop after an injury sometimes shrink on their own over time. Dogs that keep getting new cysts, or get many at once, may need a work-up for an underlying cause.
When to Call Your Vet About a Lump
Use this as a rough guide, not a substitute for your vet's advice:
- Mention it at your next visit: a lump your vet has already checked and diagnosed that hasn't changed at all.
- See your vet soon: any new lump, a lump that's changed in size, shape or color, or a pea-sized lump that has been there for a month.
- Call now: a lump that is bleeding, has burst open, is growing fast, feels hot, looks red or smells bad, seems painful, or that your dog won't stop licking or chewing.
Preventing Sebaceous Cysts on Your Dog
There's no proven way to prevent them, especially in breeds that are prone to them. What you can control is how early they're found.
- Run your hands over your dog regularly, nose to tail, during cuddles or grooming.
- Note each lump's location, size, shape and the date you found it, so your vet can tell whether it has changed.
- Tell your groomer about any bumps so they can work around them with the clippers.
Most of the bumps you find this way will turn out to be harmless. The point of checking is to catch the ones that aren't while they're still small.
Originally written by Jaclyn. Updated by the I Love Veterinary editorial team.
Sources
- Merck Veterinary Manual: Epidermal and Hair Follicle Tumors in Animals (Keratinized Cutaneous Cysts)
- Merck Veterinary Manual: Tumors of the Skin in Dogs
- Merck Veterinary Manual: Overview of Tumors of the Skin and Soft Tissues in Animals
- VCA Animal Hospitals: Cysts
- Today's Veterinary Practice: Tumor Detection in Dogs and Cats (Sue Ettinger, DVM, DACVIM)
- Canadian Veterinary Journal: Successful control of disseminated follicular cysts in a dog (Szczepanik et al., 2018)
This article is for general information and is not a substitute for advice from your veterinarian.
