Growths on dogs can look like almost anything: small, firm bumps under the skin, soft fatty lumps, dangling flaps of skin, cauliflower-textured warts, or flat discolored patches. About 65% of skin masses removed from dogs turn out to be benign, but appearance alone is not a reliable way to tell harmless from dangerous. Here’s what to look for and what different types of growths typically look like.
Soft Lumps Under the Skin
The most common soft lump you’ll feel on a dog is a lipoma, a fatty tumor that sits just beneath the skin. Lipomas feel squishy and moveable when you press on them. They’re usually round or oval, can range from marble-sized to grapefruit-sized, and the skin over them looks completely normal. They grow slowly over months or years and are almost always benign. Older dogs and overweight dogs get them more often, and some dogs develop several at once.
Another possibility is a sebaceous cyst, which forms when an oil gland gets blocked. These tend to be round, firm, and closer to the skin’s surface than lipomas. They sometimes develop a visible opening or pore at the center and may ooze a thick, whitish or grayish material. Sebaceous cysts can become red and tender if they rupture or get infected.
Bumpy or Cauliflower-Like Growths
Sebaceous gland tumors are extremely common in dogs, particularly on the head and eyelids. They often have a round, cauliflower-like texture, and some secrete a crusty material on the surface. Occasionally they bleed. On larger breeds, these growths sometimes darken to a black color, which can look alarming but is typically just pigmentation rather than a sign of cancer. To the naked eye, several types of sebaceous tumors look identical, so a vet needs to examine cells under a microscope to tell them apart.
Viral warts (papillomas) also have that rough, irregular cauliflower shape. They tend to appear in clusters, especially around the mouth, lips, and eyes of younger dogs. Warts sit on a thick base attached to the skin and are often lighter or darker than the surrounding skin. They’re caused by a virus and usually resolve on their own within a few months.
Skin Tags and Dangling Growths
Skin tags are tear-shaped flaps that dangle away from the body on a thin stalk, unlike warts which sit flat on a broad base. They’re the same color as your dog’s surrounding skin, which is one of the easiest ways to distinguish them from warts. Skin tags are harmless and common in older dogs, though they can catch on things and bleed if they’re in a spot that gets a lot of friction.
Growths That Change Size or Shape
Mast cell tumors are called “the great pretenders” because they can mimic nearly any other type of growth. They may look like an insect bite, a wart, an allergic reaction, or a harmless bump. They can appear as a raised lump on or just under the skin and may be red, ulcerated, or swollen. What makes them distinctive is their unpredictable behavior: some sit unchanged for months, then suddenly grow rapidly. Others fluctuate in size from day to day, appearing larger one morning and smaller the next. This size fluctuation happens because mast cells release histamine, which causes localized swelling that comes and goes.
Certain breeds face higher risk for mast cell tumors. Boxers, bulldogs, bullmastiffs, Boston terriers, and Staffordshire bull terriers all show increased rates, likely due to shared ancestry. Rhodesian ridgebacks, pugs, weimaraners, Labrador retrievers, beagles, and golden retrievers are also at elevated risk.
Mouth and Gum Growths
If you notice a growth inside your dog’s mouth, the most common type is an epulis, a benign mass that develops on the gums near the teeth. Epulides (the plural) account for the majority of oral tumors in dogs and usually appear as smooth, pink, firm lumps attached to the gum line. They grow slowly and can eventually interfere with eating if they get large enough.
Oral melanomas are a more serious possibility. These typically show up as brown or black masses on the gums, lips, tongue, or roof of the mouth, though some have no pigment at all and appear pink or flesh-colored. They can be flat, raised, or wrinkled in texture and often become ulcerated, meaning the surface breaks down into an open sore. Signs that a mouth growth needs urgent attention include bleeding from the mouth, drooling, bad breath that wasn’t there before, or difficulty eating.
Visual Red Flags Worth Noting
No growth can be diagnosed by appearance alone, but certain features are more common in malignant tumors. Ulceration, where the surface of the growth breaks open into a raw, wound-like area, is a warning sign. Rapid growth over days or weeks rather than months is concerning. Irregular borders, where the edges of the mass blend unevenly into surrounding tissue rather than forming a clean circle, raise suspicion. Growths that are firmly attached to deeper structures and don’t move freely when you push on them deserve prompt attention.
Color can offer clues but isn’t definitive. Dark black or mottled growths with areas of different colors (some dark, some pink) can indicate melanoma. However, some melanomas are completely unpigmented, and plenty of benign sebaceous tumors turn black. This is exactly why visual identification has limits.
How Vets Identify a Growth
The most common first step is a fine needle aspirate, where a vet inserts a small needle into the growth, withdraws some cells, and examines them under a microscope. It takes just seconds, requires no sedation in most cases, and can often provide a preliminary answer the same day. Studies show excellent accuracy when comparing fine needle aspirate results to full surgical biopsies, making it a reliable and minimally invasive starting point.
If the aspirate results are unclear or suggest something that needs a closer look, a biopsy removes a piece (or all) of the growth for more detailed analysis. This requires sedation or anesthesia but provides a definitive diagnosis, including the specific type and grade of tumor.
Tracking Growths at Home
Pick one day each week to run your hands over your dog’s entire body, checking for new lumps or changes to existing ones. When you find something, note three things: where it is, how big it is, and the date. Placing a coin or pencil eraser next to the growth and taking a photo gives you a consistent size reference over time. Some veterinary resources offer printable body maps where you can mark each lump’s location, which is especially helpful for dogs that develop multiple growths as they age.
A growth that stays the same size for months is less urgent than one that doubles in a week, but “less urgent” doesn’t mean “ignore it.” Since roughly one in three skin masses in dogs turns out to be malignant, any new lump is worth mentioning at your dog’s next vet visit, and anything that’s fast-growing, ulcerated, or changing shape warrants a sooner appointment.