Seborrheic Keratosis: Patient Information

What is Seborrheic Keratosis?

Seborrheic keratosis (often abbreviated as SK) is a very common benign skin growth that typically appears in adults during mid-life or latermy.clevelandclinic.org. These growths are non-cancerous – they do not turn into skin cancer and are not “pre-cancerous” lesionsmy.clevelandclinic.org. Because they usually arise in middle-aged and older people, SKs are sometimes nicknamed “senile warts” or “barnacles of aging,” although they are not actual wartsaad.org. In fact, most people will develop at least one SK in their lifetime, especially after age 50. It has been estimated that over 90% of adults older than 60 have one or more of these harmless spots on their skindermnetnz.org. You might have just a single growth or dozens of them over time.

What does it look like?

A close-up of a seborrheic keratosis on the skin. These growths often have a stuck-on, bumpy appearance with a waxy or warty surface.

Seborrheic keratoses can vary in appearance, but they often have a characteristic look that helps distinguish them. Common features includedermnetnz.org my.clevelandclinic.org:

“Stuck-on” appearance: SKs often look like they were pasted or glued onto the surface of the skin, rather than growing from deeper layers. They can have a slightly raised, warty or waxy surface, sometimes likened to a drop of candle wax or a piece of tree bark stuck on the skinorg my.clevelandclinic.org.
Color: Most are tan or brown, but they can range from light flesh-colored or yellowish, to dark brown or nearly black. Some even appear gray or white. It’s also common for a single lesion to have a mix of colors (due to varying pigment).
Size and shape: They are usually round or oval. Sizes can range from a few millimeters to over 2 centimeters across. Some start as small, flat bumps and may thicken or expand over timeorg.
Texture: The surface may be smooth, waxy, or rough and wart-like. If you run a finger over it, an SK will usually feel slightly raised or rough (even flat ones often have a subtle texture you can feel)clevelandclinic.org. You might notice tiny round keratin plugs or milia-like cysts on the surface – these appear as small whitish or blackish “pepper spots” and are a hallmark of SKs (caused by keratin trapped in the growth).
Location: Seborrheic keratoses can appear almost anywhere on the skin. They do not occur on palms or soles, but they are commonly found on the torso (chest, back), neck, face, and scalporg. You might see just one or a cluster of many in one area.

There are also some specific variants of SKs. For example, dermatosis papulosa nigra is a form of SK that presents as multiple small black or dark-brown spots, typically on the face (especially around the eyes and cheeks) of people with darker skin tonesmy.clevelandclinic.org. These are the same type of benign growth, just appearing as numerous tiny dark papules. Another variant, stucco keratoses, are small white or gray SKs often found on the lower legs of older individualsdermnetnz.org. Regardless of the color or variant, all these lesions are benign seborrheic keratoses.

Who gets Seborrheic Keratoses?

Seborrheic keratoses are extremely common skin growths, especially in older age groups. They can affect men and women of all racesdermnetnz.org. Some key risk factors and associations include:

Age: Age is the strongest factor. SKs are rare in young people (uncommon before age 20)org, but very common after middle age. They typically begin to appear in one’s 30s or 40s, and the number of lesions tends to increase with each decade of lifedermnetnz.org. By the senior years, almost everyone has a few SKs. In one estimate, over 90% of people over 60 have at least one SKdermnetnz.org.
Family history (Genetics): There is often an inherited tendency to develop SKs. If your parents or siblings have multiple seborrheic keratoses, you might also develop many of them over timeorg. About half of people who have numerous SKs report other family members with the same conditionmy.clevelandclinic.org.
Skin type and ethnicity: People with lighter/fair skin often develop the classic large brown SK lesions. People with darker skin tones also get SKs, but they may tend to have smaller, dark papules (such as dermatosis papulosa nigra on the face) rather than big plaquesclevelandclinic.org aad.org. In darker-skinned individuals (e.g. those of African, Asian, or Hispanic descent), SKs often appear as multiple tiny dark bumps, particularly around the eyes and cheeksmy.clevelandclinic.org.
Hormonal changes: Sometimes SKs may pop up during periods of hormonal influence. Some women report new SKs developing during pregnancy or after starting estrogen replacement therapyorg. The hormonal connection isn’t fully understood, but it’s an observed association.
Sun exposure: Sunlight might play a role in the development of SKs, though it’s not the whole story. Studies have noted that SKs tend to appear on sun-exposed skin (like the face, arms, and back) and that sun-damaged skin can spur these growthsorg. There are even cases where a sunburn was followed by a crop of new SKs in that areadermnetnz.org. However, SKs also occur on skin that never sees the sun (like under clothing), so sun exposure is not the sole causeaad.org. Still, lifelong sun exposure might increase the likelihood or number of SK lesions.
Friction: SKs often develop in skin folds or areas of friction (under the breasts, in the groin, along the collar line). Chronic rubbing or friction might contribute to their appearance in these locationsorg.

Importantly, seborrheic keratoses are not contagious. You cannot “catch” them from someone else, and they don’t spread from one part of your body to another by touchaad.org. If it seems like they are “spreading,” it’s only because new ones may be developing as time goes on. Also, despite the name, they have nothing to do with seborrhea (oily skin or dandruff) – the term “seborrheic” in the name is a bit misleadingdermnetnz.org.

Multiple seborrheic keratoses on the back of an older individual. It’s common for people to develop many of these “stuck-on” brown spots as they age.

Because SKs are so common in older adults, you might hear them referred to humorously as “barnacles” or signs of wisdom/age. Some people have just a few, while others can have hundreds of lesions scattered over their skin. Having a lot of SKs does not mean anything is wrong internally – some individuals simply inherit the tendency to grow many of these benign spotsdermnetnz.org.

What causes these growths?

The exact cause of seborrheic keratoses is still not fully understooddermnetnz.org. Researchers consider them to be a degenerative change of the skin associated with aging, combined with genetic factorsdermnetnz.org. In other words, as the skin gets older, its cells may start growing in this irregular pattern, forming SKs – and some people are more prone to it than others due to their genesdermnetnz.org.

Some important points about causes and myths:

Not caused by a virus: Although SKs can look warty, studies suggest there is no viral cause (like human papillomavirus, which causes true warts)org. Unlike common warts, SKs are not triggered by an infection.
Genetic mutations: Scientists have found certain gene mutations within the cells of SKs – for example, changes in genes like FGFR3, PIK3CA, RAS, AKT1, EGFR, etc., have been identified in these growthsorg. These mutations likely drive the skin cells to grow into an SK. Many of the same mutations are found in other harmless skin lesions (like solar lentigines, or “age spots”), suggesting aging and UV exposure might induce these changesdermnetnz.org. Importantly, these are benign mutations – they do not make the lesion malignant.
Possible triggers: As mentioned, sun exposure or skin irritation might act as triggers in some cases. There have been reports of a sudden eruption of SKs after intense sun exposure (sunburn) or after eczema (dermatitis) in an areaorg. Chronic friction (such as under clothing or in folds) is also thought to possibly stimulate SKs in those spotsdermnetnz.org. Additionally, certain medications (like some chemotherapy drugs or biologic medications) can lead to an outbreak of SK-like lesions as a side effectdermnetnz.org.
Not related to sebaceous glands: Despite the name “seborrheic,” SKs do not come from oil glands or have anything to do with sebum (skin oil)org. The name probably came about because they often occur on trunk and face (areas that also have sebaceous glands), but that is just coincidence.
Not your fault: There’s nothing you did to cause seborrheic keratoses – they are not caused by any known lifestyle factor aside from possibly sun exposure. They are a natural occurrence in the skin for many people as they age. You cannot prevent them (there is no known way to stop SKs from forming)org.

Microscopic view (histology) of a seborrheic keratosis. The epidermis (outer skin layer) is thickened and shows clusters of basaloid cells and squamous cells, along with characteristic horn cysts (round keratin-filled cysts) within the lesioncommons.wikimedia.org.

Under the microscope, a seborrheic keratosis consists of a proliferation of normal epidermal cells that have piled up into a benign tumor. The histology typically shows thickened epidermis with both small basal-type cells and flatter squamous cells in the growthcommons.wikimedia.org. Horn cysts (tiny keratin-filled cystic spaces) are often seen – these appear as little round whitish cysts within the lesioncommons.wikimedia.org. These microscopic features help confirm that an SK is made of excess keratin and skin cells, consistent with a benign keratinocyte tumor. There is no invasive growth into deeper skin – SKs sit on the surface, which is why they look “stuck on.”

Do SKs cause any symptoms?

Most of the time, seborrheic keratoses are asymptomatic – meaning they usually don’t hurt or cause physical symptoms. Many people don’t even realize they have them until they notice the appearance. However, some minor symptoms or issues can occur:

Itching or irritation: SKs can sometimes itch, especially if they are dry or in an area that gets rubbed by clothing. Scratching an itchy SK may make it more irritated or even cause it to bleed a little.
Inflammation: An SK can get irritated or inflamed if it’s repeatedly traumatized (for example, one on a collar line might get rubbed by a shirt, or one under a bra strap might get irritated). An inflamed SK may become red, crusty, or tender – this is called an “irritated seborrheic keratosis.” It might be hard to distinguish from a scab or skin cancer when it’s inflamed, because it can turn reddish. The surrounding skin can even get a bit of eczema (red, dry patch) as a reaction to an irritated SKorg.
Snagging or bleeding: If an SK is thick or protruding, it might catch on jewelry or clothing. If it gets caught, the lesion can tear or bleed superficially. This is usually minor, but if a lesion is frequently snagging or bleeding, many patients choose to have that one removed for comfort.
Cosmetic concerns: The most common “symptom,” though not medical, is that people may find SKs unsightly. They can be cosmetically bothersome, especially if they occur on visible areas like the face or neck. Large or very dark lesions might cause someone to feel self-conscious. This often drives the decision to remove them, even though medically they do not need removal.

Are seborrheic keratoses dangerous?

No – seborrheic keratoses are benign and not dangerous. They do not turn into skin cancer, and having SKs does not increase your risk of skin cancermy.clevelandclinic.org. In fact, SKs are made up of normal skin cells, just growing in a greater number. They are often compared to moles or skin tags in that sense – a growth of your own cells that is not harmful.

That said, there are a couple of important caveats to be aware of:

Appearance can mimic skin cancer: Seborrheic keratoses can sometimes look similar to other skin lesions, including skin cancers like melanoma or squamous cell carcinoma. For example, a very dark SK with irregular shape might be mistaken for a melanoma at first glance. Dermatologists are usually able to tell the difference by close examination (often using a dermatoscope), because SKs have some distinctive patterns (like those keratin cysts or a waxy texture)org. However, if there is any doubt, a doctor will perform a biopsy (remove a piece or the whole lesion) to check it under the microscope and confirm it’s not cancerdermnetnz.org. Skin cancers can coincidentally occur near or even under an SK (though this is uncommon)dermnetnz.org, so suspicious features should always be evaluated. In short, if you have a “seborrheic keratosis” that is changing, bleeding a lot, or just doesn’t quite look like your others, have a doctor examine it to rule out a skin cancer.
“Sign of Leser-Trélat”: In very rare cases, a sudden explosion of numerous SKs all at once can (potentially) be a sign of an internal cancer. This is known as the Leser-Trélat signorg. For example, some patients with an internal malignancy (like a stomach or colon cancer) have reported dozens of SKs popping up rapidly. However, this is extremely uncommon and somewhat controversial – the link isn’t proven and might be a coincidence in many casesmy.clevelandclinic.org. Most of the time, people get new SKs simply as part of the aging process, not because of any internal problem. Doctors might investigate further if someone suddenly develops an unusually large number of SKs in a short time, but again, this scenario is rare. (When SKs appear gradually over years, it is not concerning.)
Not pre-cancerous: Unlike some other skin growths (for example, actinic keratoses are precancerous lesions caused by sun damage), seborrheic keratoses have no risk of turning into cancer. They are a “dead end” growth of the skin – once a lesion is an SK, it stays an SK (it might enlarge or get more raised, but it won’t transform into something malignant). Research has not found tumor-suppressor gene mutations in SKs, which supports the fact that they don’t progress to cancerorg dermnetnz.org.

The main risks from SKs are therefore not from the lesions themselves, but rather the chance of mistaking a skin cancer for an SK. This is why it’s a good idea to have new or unusual skin growths checked by a healthcare provider. If you have a long-standing SK that hasn’t changed, it’s fine. But if you notice a new “seborrheic keratosis” that appeared out of the blue, or if an existing one begins to change in appearance rapidly, bleed, or ulcerate, those are signs to get it evaluated (just to be safe that it isn’t something else).

When should I see a doctor?

You should consider seeing a doctor (usually a dermatologist) in the following situations:

Uncertain diagnosis: If you have a new skin growth and you are not 100% sure it’s a seborrheic keratosis, get it checked. As noted, SKs can resemble skin cancers and vice versa. Dermatologists can usually identify an SK by examination. If there’s any doubt, the doctor can perform a quick biopsy. This is the only way to know for sure that a suspicious growth isn’t cancerorg. When in doubt, check it out.
Changes in a lesion: If one of your existing SKs changes in size, color, or shape, or starts to have symptoms like a lot of bleeding or pain, have it examined. While SKs themselves don’t turn cancerous, it’s possible for a skin cancer to develop very close to or within an SK (though rare)org. A change could also mean it wasn’t an SK to begin with.
Sudden eruption of many lesions: If you somehow develop a shower of dozens of new SKs within a short period (say, a few months), bring this up with your doctor. They might investigate for internal causes (like checking general health or doing age-appropriate cancer screenings) just to rule out the exceedingly rare Leser-Trélat associationorg. It’s more likely a harmless idiopathic eruption or “pseudo-Leser-Trélat,” but it’s worth a mention to your physician.
Irritation or discomfort: If an SK is constantly irritated (itchy, inflamed, catching on things) and causing you discomfort, you can see a doctor to discuss removal. Even though benign, it may be worth removing if it’s in a bad spot that keeps getting traumatized.
Cosmetic or psychological concern: If you simply dislike the appearance of a seborrheic keratosis – for example, if it’s large and on your face or if you have many and it affects your confidence – you can consult a dermatologist about removal options. This is an elective reason, but it’s valid if it bothers you. Dermatologists remove SKs frequently for cosmetic reasons.

In summary, any time you are not completely sure a skin growth is a harmless SK, or if something about it changes, it’s wise to have a medical professional evaluate it. Once a diagnosis of seborrheic keratosis is confirmed, there is usually no medical need to treat it (unless you want it removed for comfort or cosmetic reasons).

How are seborrheic keratoses treated?

Because seborrheic keratoses are benign and generally harmless, treatment is optional. Many people choose to simply leave them alone, especially if the lesions are small or in inconspicuous areas. No treatment is required for your healthaad.org. However, there are several effective treatment methods to remove seborrheic keratoses if needed. Common reasons for removal include: the lesion is cosmetically undesired, is itching or gets irritated often, or there’s uncertainty about the diagnosis and a biopsy is warrantedaad.org. Removal of SKs is typically done in a doctor’s office with minimal downtime. Here are the typical treatment options:

Cryotherapy (Freezing): This is one of the most common methods. The doctor applies liquid nitrogen (an extremely cold spray or cotton swab) to freeze the SKorg. The frozen growth then typically falls off within days as the skin underneath healsaad.org. Sometimes a blister forms and then scabs over before falling off. Pros: Quick, no injections or cutting needed. Cons: It can cause temporary redness or a blister. Also, freezing can sometimes leave behind a lighter-colored patch of skin (loss of pigment) at the treatment sitemy.clevelandclinic.org. In most cases this fades over time, but it can be permanent in some individualsaad.org. The risk of a hypopigmented (light) spot or slight scar is higher on the face or neck and in people with darker skin tonesdermnetnz.org. For this reason, some dermatologists use cryotherapy cautiously (or not at all) on the face to avoid any noticeable discoloration.
Shave excision (tangential removal): In this method, the area is numbed with a small injection of local anesthetic, and the doctor uses a blade to shave off the lesion flush with the skin surfaceclevelandclinic.org. Often, they will then lightly cauterize or use a curette to gently scrape any remaining cells and stop bleedingmy.clevelandclinic.org. Stitches are usually not needed. This technique physically removes the SK and allows it to be sent to pathology for confirmation under the microscope (useful if there was any doubt about diagnosis)my.clevelandclinic.org. Pros: Immediate removal, and you get a tissue diagnosis if needed. Cons: Requires local anesthesia (a needle), and there will be a superficial scab that heals over about 1–2 weeks. There is a small risk of a mild scar, but generally this heals very well with minimal trace.
Curettage and Electrocautery: This is a minor surgical method where, after numbing the skin, the doctor uses a curette (a sharp, spoon-like instrument) to scrape off the lesion and an electrocautery device to burn or cauterize the baseclevelandclinic.org. Electrocautery helps destroy any remaining cells and stops bleeding. This method is often used for thicker or more stubborn SKs, or for those that might not fall off easily with freezing. Pros: Very effective, and bleeding is controlled. Cons: Like shave removal, it involves a small procedure with local anesthesia. There will be a little wound that heals in 1–2 weeks. It could leave a slight mark or lighter spot, but usually low risk of significant scarringmy.clevelandclinic.org.
Laser ablation: Various laser treatments (such as CO₂ laser or Erbium:YAG laser) can vaporize the SK tissue. The dermatologist targets the lesion with a laser, which burns away the growth layer by layerclevelandclinic.org. This is often done with local anesthetic as well. Pros: Lasers can remove the lesion with precision and tend to have good cosmetic results, often leaving very little trace once healedmy.clevelandclinic.org. It’s a relatively quick procedure. Cons: It may be a bit more expensive (special equipment) and the treated area will be like a superficial burn that needs to heal over about 1–2 weeks. There can be temporary redness as it heals, and standard wound care is needed.
Chemical treatment: For very small or flat SKs, sometimes doctors use a chemical peel or solution. A common example is applying a bit of trichloroacetic acid (TCA) to the spot to cause it to peel offorg. This essentially “burns” the lesion chemically. Another newer option is a 40% hydrogen peroxide solution that has been FDA-approved specifically for treating seborrheic keratosesmy.clevelandclinic.org. This high-strength hydrogen peroxide (much stronger than household peroxide) is applied in the office with a special applicator pen, usually repeated several times in one sessionmy.clevelandclinic.org. It causes the lesion to crust and fall off. Pros: No cutting or freezing, useful for patients who can’t tolerate other methods. Cons: These may not work as well for larger SKs and might require multiple treatments. They can cause temporary irritation like redness or stinging at the application sitemy.clevelandclinic.org.
Topical creams (experimental): Generally, topical home treatments are not very effective for SKs, but there is some research into creams that may shrink or lighten For instance, prescription strength tazarotene cream (a retinoid) or strong alpha-hydroxy acid creams/peels have shown some ability to flatten SKs over timemy.clevelandclinic.org. Vitamin D3 cream has also been triedmy.clevelandclinic.org. These treatments would take weeks of daily use and might only partially improve the lesions. Currently, there is no reliably effective at-home cream to make SKs go away completely, so most people end up having bothersome lesions removed by a procedure instead.

All of the removal methods have potential advantages and drawbacks. No method is guaranteed to leave zero trace, so discuss with your doctor which option might give the best cosmetic result for your particular lesion(s). A small lighter or darker patch can remain after removal, but in many cases it fades with timeaad.org. People with darker skin need to be especially careful, as treatments like freezing or laser can cause post-inflammatory hypopigmentation or hyperpigmentation (skin lightening or darkening) at the spotdermnetnz.org. Make sure to follow any wound care instructions after removal to help it heal well. The good news is that most removed seborrheic keratoses do not come back in the same spotaad.org. Once gone, that individual lesion is usually gone for good. However, removing one does not prevent new ones from appearing elsewhere – you might get others over the years in different locations, since the underlying tendency remainsmy.clevelandclinic.org.

Note: Never attempt to pick, scrape, or burn off a suspected seborrheic keratosis yourself at home. Not only could this lead to infection or scarring, but there’s also the risk that you misidentify the lesion – if it were actually a skin cancer, you’d be delaying proper care. It’s always safest to have a doctor evaluate and remove these growths using sterile technique.

What is the outlook for someone with SKs?

The overall outlook is excellent, because seborrheic keratoses are benign. They usually just persist as a cosmetic issue. Here are a few final points on what to expect:

Persistence: Once an SK appears, it tends to stick around. Some SKs may grow thicker or darker slowly over time. On occasion, a small SK might even fall off on its own or go away (especially if it undergoes inflammation or a process called lichenoid dermatitis)org, but this is not very common. Most will remain until removed.
More lesions over time: You will likely develop more SKs as you get older. There is no set number – some people might only ever get a handful, while others continue to get new ones periodically. There is no known prevention for new SKsorg. Keeping sun-safe (using sunscreen, etc.) is good for your skin health in general and may possibly slow down some sun-related skin changes, but it won’t guarantee prevention of SKs (since they also occur on non-sun-exposed skin).
No health impact: Remember that SKs are simply a nuisance, not a threat. They won’t affect your longevity or general health. Many people end up with lots of “barnacles” on their skin as they age and live perfectly healthy lives with them. They are essentially a benign sign of skin aging.
Managing as needed: If your SKs don’t bother you, you can ignore them. If they do bother you (or new ones appear that cause concern), you can always have them evaluated and removed. There is no harm in removing SKs if that’s your preference; just be aware that new ones might pop up elsewhere later. Think of it like weeds in a garden – you can pluck the ones you see, but new seeds may sprout over time.

In summary, seborrheic keratoses are a normal and common part of getting older for many people. They are benign growths that can be left alone safely. If needed, they can be removed with minor procedures. If you have any doubt about a skin lesion, get it checked – otherwise, you can generally relax knowing that these “stuck-on” spots are harmless.

Sources

Cleveland Clinic – Seborrheic Keratosis: Causes, Symptoms, and Treatment. A comprehensive patient health library article confirming that seborrheic keratoses are common benign skin growths that appear in middle age and increase with age. It notes that about 75% of people have at least one by age 70, and that they are harmless (not pre-cancerous)my.clevelandclinic.org my.clevelandclinic.org. The article also describes the clinical appearance (“stuck on,” waxy, brown), risk factors (age, family history, lighter skin vs. dermatosis papulosa nigra in darker skin), and management options including cryotherapy, curettage, shave excision, lasers, and a 40% hydrogen peroxide solutionmy.clevelandclinic.org my.clevelandclinic.org my.clevelandclinic.org my.clevelandclinic.org. It explains that removal is elective and post-treatment skin lightening can occurmy.clevelandclinic.org. (Reviewed 08/27/2021)
DermNet NZ – Seborrhoeic Keratosis. An educational resource by dermatologists detailing SKs. Confirms that over 90% of adults over 60 have at least one SKdermnetnz.org. Explains that the cause is not fully known but is associated with aging and genetic factors; notes that a viral cause is unlikely and mentions identified mutations in FGFR3, PIK3CA, and other genes in SK cellsdermnetnz.org. Describes the clinical features: they can be flat or raised, 1 mm to several cm, various colors (yellow, brown, black), with a waxy or warty surface and a “stuck on” appearancedermnetnz.org. Also outlines treatment methods (cryotherapy, curettage, laser, etc.) and warns that post-treatment loss of pigmentation can be an issue, especially for dark-skinned patientsdermnetnz.org. The page also notes that SKs are not premalignant but can occasionally be hard to distinguish from skin cancer, and it mentions the rare sign of Leser-Trélat (eruptive SKs associated with internal malignancy)dermnetnz.org. (DermNet, updated Jan 2016)
American Academy of Dermatology (AAD) – Seborrheic Keratoses: Overview, Causes, and Treatment. AAD’s patient info emphasizes that seborrheic keratoses are common, harmless growths that can look like warts or even skin cancer, but are non-cancerousaad.org. It mentions they’re often called the “barnacles of aging” and usually appear in middle age or lateraad.org. The AAD notes that people with fair skin and a family history are more prone, but that SKs also appear in those with medium to dark skin (often as small dark papules in the eye area)aad.org. It states the cause is unknown but possibly related to sun exposure and genetics, and definitively notes they are not contagiousaad.org. In terms of treatment, AAD describes cryosurgery (freezing) as a common method and cautions that after removal the skin may be lighter than surrounding skin – usually fading with time but sometimes permanentaad.org. It reinforces that most SKs don’t need treatment unless they are cosmetically unwanted or suspicious for canceraad.org. (AAD Public Information, last updated 2023)
DermNet NZ – Seborrhoeic Keratosis Pathology & Variants. (Supplementary) Provides insight into the histology of SKs, describing features like basaloid and squamous proliferation and horn cystscommons.wikimedia.org. Also discusses variants such as dermatosis papulosa nigra and stucco keratosisdermnetnz.org. This source was used for details on microscopic characteristics and the existence of different subtypes, confirming that SKs are composed of proliferating epidermal keratinocytes and are confined to the epidermis.