A sebaceous cyst on a dog looks like a small, raised, round bump sitting on or just beneath the skin’s surface. It typically feels firm but slightly squishy, and the skin over it may look normal or have a slightly bluish tint. These cysts grow slowly, usually ranging from pea-sized to about the size of a marble, though some can grow larger over time.
What a Sebaceous Cyst Looks Like Up Close
Sebaceous cysts form when oil-producing glands in the skin become blocked. The gland keeps producing its thick, oily material (called sebum) with nowhere for it to go, so a small sac fills up beneath the surface. The result is a raised, dome-shaped lump that you can usually feel rolling slightly under your fingertip.
The cyst itself is typically skin-colored or slightly pale. If it ruptures, it releases a white, paste-like discharge that can look like thick toothpaste. Some cysts ooze a yellow or brown material instead, especially if they’ve been present for a while. The discharge may have an unpleasant smell. An intact cyst that hasn’t ruptured will simply look like a smooth, round bump with no visible opening.
Where They Usually Appear
These cysts most commonly show up on the head, neck, torso, or upper legs. You might spot one while petting your dog or during a bath. They can appear anywhere there are oil glands, but these four areas account for the majority of cases. Dogs can develop a single cyst or several at once, and older dogs tend to accumulate more of them over time.
Breeds More Likely to Get Them
Any dog can develop a sebaceous cyst, but certain breeds are more prone. Basset Hounds, Boxers, English Springer Spaniels, Schnauzers, and Golden Retrievers all have a higher predisposition. Terrier breeds and hairless breeds are particularly susceptible to follicular cysts, a closely related type. Chinese Crested dogs, for example, are prone to blocked skin ducts that resemble blackheads, because their skin pigment doesn’t activate strongly and their pores clog easily.
How to Tell It Apart From Other Lumps
Not every bump on your dog is a sebaceous cyst, and several other growths can look similar at first glance. Knowing the key differences can help you gauge how urgently your dog needs to be seen.
Sebaceous Cyst vs. Lipoma
Lipomas are benign fatty tumors that are soft, rounded, and usually movable under the skin. They feel like a squishy ball that slides around when you press on it. Sebaceous cysts tend to feel firmer and sit closer to the skin’s surface, while lipomas are deeper and more rubbery. Lipomas are most common in older or overweight dogs and almost never discharge any material. If the lump oozes a thick, pasty substance, it’s more likely a cyst than a lipoma.
Sebaceous Cyst vs. Mast Cell Tumor
This is the comparison that matters most. Mast cell tumors are the most common malignant skin tumor in dogs, and they can sometimes mimic the appearance of a harmless cyst. A key visual difference: mast cell tumors and other round cell tumors commonly appear as red, raised, hairless masses. They may change size rapidly, sometimes swelling and shrinking within days. A sebaceous cyst, by contrast, grows very slowly, keeps its hair covering, and stays roughly the same color as the surrounding skin. But appearance alone is not reliable enough to rule out cancer, which is why any new lump deserves a veterinary check.
Signs a Cyst Has Become Infected
Sebaceous cysts are benign and often cause no problems at all. But they can become infected, and when they do, the signs are fairly obvious. The area around the cyst turns red, swollen, and warm to the touch. Your dog may lick or scratch at it because it becomes itchy or painful. The cyst may start oozing thick white, yellow, or brown material. If the surrounding skin looks angry or your dog seems bothered by it, a vet can take a sample to identify the bacteria involved and prescribe the right antibiotic.
An infected cyst can also burst on its own, leaving an open wound that’s vulnerable to further infection. Keeping the area clean and preventing your dog from licking it are the immediate priorities if this happens.
How Vets Confirm the Diagnosis
No one can confirm a sebaceous cyst just by looking at it. Even experienced veterinarians cannot reliably distinguish a benign growth from something more concerning based on appearance alone. The standard approach is to insert a small needle into the lump and withdraw a sample of cells, a quick procedure your dog barely feels. The cells are examined under a microscope to confirm what the lump actually is.
A sebaceous cyst will yield thick, oily debris. Follicular cysts, a closely related type, contain a crumbly, cheese-like material made of skin protein. If the sample raises any questions about the type of growth, a biopsy of the removed tissue provides a definitive answer.
When Removal Makes Sense
Many sebaceous cysts are harmless enough to leave alone. A small, stable cyst that doesn’t bother your dog and isn’t in a spot where it gets irritated by a collar or harness can simply be monitored. You’ll want to check it periodically for changes in size, shape, color, or texture.
Removal becomes the better option when a cyst keeps getting infected, grows large enough to cause discomfort, or sits in a location where it’s constantly being rubbed or bumped. There’s also a practical argument for removing any sebaceous growth rather than watching it indefinitely. Because it’s not possible to distinguish a low-grade malignant growth from a benign one without examining the tissue under a microscope, surgical removal eliminates the uncertainty. The procedure is straightforward, typically done under local or general anesthesia, and most dogs recover within a week or two with minimal fuss.
If your dog develops multiple cysts or new ones appear frequently, your vet may recommend a broader skin health evaluation to look for underlying causes like hormonal imbalances or chronic skin conditions that are driving the blockages.