In dermatology, SK stands for seborrheic keratosis, one of the most common benign skin growths in adults. These are noncancerous raised spots that typically appear after age 30 and become increasingly common with age. By age 50, virtually everyone has at least one. They’re harmless in the vast majority of cases, but their appearance can mimic more serious skin conditions, which is why they get so much attention in dermatology offices.
What Seborrheic Keratoses Look and Feel Like
SKs have a distinctive “pasted on” or “stuck on” look, as if someone dripped candle wax onto the skin and let it harden. They’re usually round or oval, range from light tan to dark brown or black, and can feel waxy, rough, or scaly to the touch. Some are flat with a textured surface, while others are noticeably raised. They range in size from a few millimeters to over an inch across.
They show up most often on the face, chest, shoulders, and back, though they can appear nearly anywhere except the palms and soles. Most people develop multiple SKs over time, and it’s common to have dozens by older age. They don’t hurt, though they can become irritated if clothing or jewelry rubs against them. Occasionally an SK will itch, especially if it’s in a friction-prone area.
What Causes Them
SKs develop when skin cells called keratinocytes start multiplying faster than normal in a localized spot. Research shows these growths are driven by specific genetic mutations within individual skin cells. The most common mutations affect a gene called FGFR3, found in roughly 40 to 85 percent of SKs, along with mutations in PIK3CA, present in about 40 percent. Both of these drive cell growth, but a built-in feedback mechanism keeps the growth well-differentiated and prevents it from turning malignant. This is why SKs, despite carrying mutations found in some cancers, remain benign.
Sun exposure, aging, and genetics all play a role in who gets more SKs and how early they appear. They tend to run in families, and people with lighter skin often develop more of them. They are not contagious and are not caused by a virus (unlike warts, which they sometimes resemble).
How Dermatologists Identify SKs
Most SKs are diagnosed by appearance alone. An experienced dermatologist can usually recognize one at a glance based on that characteristic stuck-on look, waxy texture, and location. When there’s any uncertainty, a dermatologist will use a dermatoscope, a handheld magnifying device with a built-in light, to examine the growth more closely.
Under dermatoscopy, SKs show specific features that help distinguish them from other growths. The most recognizable are milia-like cysts: tiny white or yellowish round structures embedded in the lesion that look like bright stars against a darker background. Comedo-like openings, which resemble small dark plugs similar to blackheads, are another hallmark. Together, these features give dermatologists high confidence in the diagnosis without needing a biopsy.
The tricky part is that some melanomas can mimic the appearance of an SK, even under a dermatoscope. Features like a blue-black color within the growth, irregular dots or streaks, or a blue-white veil are red flags that suggest the lesion might not be a simple SK. If any of these are present, or if a growth is changing rapidly, a biopsy is typically performed to rule out melanoma or another skin cancer.
When SKs Signal Something Else
A single SK is meaningless from a health standpoint. However, a sudden eruption of many seborrheic keratoses over a short period is known as the sign of Leser-Trélat, and it can occasionally point to an internal cancer. This is rare, but when it occurs, the associated malignancy is most often an adenocarcinoma of the colon, breast, or stomach. About 20 percent of cases involve a lymphoma or leukemia instead. The key distinction is the rapid, explosive onset of numerous new SKs, not the presence of a few that developed gradually over years.
Removal Options
Because SKs are benign, removal is considered cosmetic in most cases and isn’t medically necessary. That said, many people want them removed because they’re unsightly, irritating, or in a spot that catches on clothing. Several options exist, and the choice usually comes down to location, size, and personal preference.
Cryotherapy (freezing with liquid nitrogen) and electrodesiccation (using a small electrical current to destroy the tissue) are the two most common in-office procedures. Both are quick, performed with local numbing, and have similar success rates. In one comparative study, both methods effectively removed about 81 percent of treated lesions at eight weeks, with no significant difference in outcomes. Cryotherapy tends to cause more pain during the procedure, while electrodesiccation may offer slightly more precision for smaller lesions.
Laser ablation is another option, particularly for facial SKs where cosmetic outcome matters most. Er:YAG laser treatment achieved complete clearance in 80 percent of cases in one study, typically in a single session. The tradeoff is a longer healing time of about 10 days, and roughly 14 percent of treated patients experienced mild scarring. Post-treatment redness is common but usually temporary.
For people who want to avoid procedures entirely, a topical 40 percent hydrogen peroxide solution was approved by the FDA in 2017 specifically for treating SKs. It’s applied in a clinical setting, not at home. Results are modest compared to procedural options: in the two large clinical trials that led to approval, complete clearance of all treated lesions occurred in only 4 to 8 percent of patients. It works better for thinner, flatter SKs and may require multiple applications.
What to Expect After Removal
After any removal procedure, the treated area typically forms a small scab that falls off within one to three weeks. Some temporary redness or discoloration at the site is normal, especially on darker skin tones, where post-inflammatory hyperpigmentation can linger for weeks to months. SKs do not recur in the exact same spot once fully removed, but new ones can and often do develop nearby or elsewhere on the body over time. There’s no way to prevent new SKs from forming.