Seborrheic keratosis is the most common benign skin tumor, affecting over 80 million Americans. These noncancerous growths are made up of immature skin cells called keratinocytes and are covered in keratin, the same fibrous protein that makes up your fingernails. They’re slow-growing, harmless, and almost never require treatment for medical reasons. An estimated 90% of adults over age 60 have at least one.
What They Look and Feel Like
Seborrheic keratoses have a distinctive appearance that, once you’ve seen one, becomes easy to recognize. They look like waxy, slightly raised bumps that seem “pasted on” to the skin, as if a drop of candle wax landed and hardened there. They’re usually round or oval, with a rough or scaly surface, and they range in color from light tan to brown to black. Some are flat, while others are noticeably raised and bumpy.
They show up most often on the face, chest, shoulders, and back, though they can appear nearly anywhere except the palms of your hands and soles of your feet. You might develop just one or dozens over time. They don’t hurt, but they can become irritated if clothing or jewelry rubs against them, and some people find them itchy.
Causes and Risk Factors
Aging is the biggest risk factor. Seborrheic keratoses rarely appear before age 30, and they become increasingly common with each decade of life. Sun exposure plays a role too. Genetic studies show that the mutations driving these growths carry a UV signature, meaning the DNA changes match the pattern caused by ultraviolet radiation. That said, seborrheic keratoses also develop on skin that rarely sees the sun, so UV light isn’t the whole story.
Each growth starts from a single mutated skin cell that begins copying itself. Nearly half of seborrheic keratoses carry a mutation in a gene called FGFR3, which promotes cell growth. Other growth-related genes are frequently mutated as well. What keeps these growths benign, despite having mutations in genes also seen in cancers, is a built-in feedback loop that keeps the cells well-differentiated. They proliferate more than normal skin cells, but they don’t become disorganized or invasive the way cancer cells do. There’s also a hereditary component: if your parents developed many of them, you’re more likely to as well.
How Doctors Tell Them Apart From Skin Cancer
Most seborrheic keratoses are easy for a dermatologist to identify on sight. When a growth is darker, irregularly shaped, or otherwise ambiguous, a dermatologist will use a handheld magnifying tool called a dermatoscope. Under magnification, seborrheic keratoses show characteristic patterns: tiny white cysts embedded in the surface, small dark plug-like openings, and a pattern of ridges and fissures. One large study found these plug-like openings in 71% of pigmented seborrheic keratoses and white cysts in 66%.
The challenge is that some melanomas can mimic seborrheic keratoses. Research published in JAMA Dermatology found that certain features visible under a dermatoscope, particularly a blue-black coloring pattern, are the strongest clue that a growth thought to be a seborrheic keratosis is actually melanoma. If there’s any doubt, a dermatologist will take a small skin sample and send it for lab analysis. This is why any growth that changes rapidly, bleeds without clear cause, or looks different from your other spots is worth getting checked.
When and Why People Get Them Removed
Because seborrheic keratoses are benign, removal is entirely optional. People choose to have them removed for cosmetic reasons, because they’re in a spot that gets irritated by clothing, or because a growth is catching on things. Insurance typically doesn’t cover removal when it’s purely cosmetic.
The three most common removal methods are:
- Cryotherapy: The growth is frozen with liquid nitrogen. This works well for thinner, flatter growths. The area may blister afterward and typically lightens or darkens slightly compared to surrounding skin.
- Curettage (scraping): After numbing the area, the doctor uses a blade to scrape the growth off the skin’s surface. This is sometimes combined with cryotherapy for flatter growths.
- Electrocautery (burning): The area is numbed and the growth is destroyed with an electric current. This method works well for thicker, more raised growths, often combined with scraping.
A prescription topical treatment containing a high concentration of hydrogen peroxide is also available. It’s applied in a doctor’s office, not at home, and a second treatment may be needed after three weeks if the growth doesn’t fully resolve.
What to Expect After Removal
All removal methods carry a small risk of leaving a lighter or darker patch of skin where the growth was. This color change is more noticeable in people with darker skin tones. Scarring is possible but uncommon with standard techniques, since these growths sit on the skin’s surface rather than extending deep into it. The treated area typically heals within a few weeks, forming a scab that falls off on its own.
A removed seborrheic keratosis generally doesn’t grow back in the same spot. However, removal doesn’t prevent new growths from developing elsewhere. If you’re prone to developing them, new ones will likely continue to appear over time, and there is no known way to prevent that.