What Causes Seborrheic Keratosis? A Dermatologist Explains How to Tell It Apart from Moles, Small Dark Spots and Skin Cancer, and How to Remove It Smoothly Without Scarring
Seborrheic keratosis is one of the most common benign skin growths to appear with age. It looks like a raised bump or a rough, raised patch that seems "stuck on" the skin. It is not cancer and not contagious. In everyday practice, though, it is the lesion people ask about most often, because "it cannot always be told apart from skin cancer by eye alone", especially darker ones or ones that have been scratched until inflamed. In this article, a dermatologist explains how it forms, the subtypes most often seen in Thai patients, the features doctors use to diagnose it including skin scope examination (dermoscopy), how to tell it from look-alike lesions, the warning signs that need prompt attention, and how to choose a removal method suited to Asian skin to reduce the chance of dark marks and scarring.
What causes seborrheic keratosis?
Seborrheic keratosis comes from an increase in the number of epidermal skin cells (keratinocytes), which thicken into a growth. Biologically, it is linked to non-dangerous mutations in certain genes in skin cells, such as FGFR3 and PIK3CA. It is therefore a local change: not an infection, and it does not progress into cancer. Things worth understanding correctly:
It is not caused by clogged oil or poor hygiene. Although the name contains the word seborrheic, it is not directly related to the oil glands.
It is not caused by a virus. This differs from warts, which are caused by HPV, and it does not spread to other people or by scratching.
It is mainly related to age and genetics. It usually starts in middle age and increases in number with age. People with a family history often have several spots.
Accumulated sun exposure contributes in some locations, especially the face and neck.
There are several subtypes of seborrheic keratosis
Lumping everything together as "seborrheic keratosis" gives the impression of a single kind of mark, but there are actually several subtypes whose appearance and care differ.
Common seborrheic keratosis (common / acanthotic type)
A raised bump or patch, light brown to black, with a rough surface that may be shiny or scaly, looking stuck on the skin. It can appear anywhere on the body, especially the trunk, back and face.
Small dark bumps on the cheeks (Dermatosis papulosa nigra – DPN)
Very common in people with darker skin, including Thai people. These are many small dark brown to black bumps over the cheekbones and around the eyes. It is considered a type of seborrheic keratosis. It often begins in the late teens and increases in number with age. This is the group of patients most concerned about appearance.
Stucco keratosis
Small, dry, whitish-gray bumps on the shins and ankles that can be rubbed off like dried plaster. Common in older adults.
Irritated seborrheic keratosis
A seborrheic keratosis that is rubbed by clothing or a bra strap, or scratched, becomes swollen, red, itchy and scaly, and may bleed. Its appearance changes until it looks like skin cancer, which is an important reason to have it examined by a doctor.
How doctors diagnose seborrheic keratosis, and the role of dermoscopy
A dermatologist does not rely on the naked eye alone but uses a skin scope (dermoscope), which helps distinguish seborrheic keratosis from cancer far more accurately. Features of seborrheic keratosis under the scope that doctors look for include:
Small pearl-like white cysts (milia-like cysts) scattered through the lesion
Openings resembling blackheads (comedo-like openings) in brown-black
Grooves and ridges like the surface of the brain or a fingerprint (cerebriform / gyri and sulci)
A sharply defined edge as if nibbled by insects (moth-eaten border) in the flat type
If the features under the scope do not clearly fit seborrheic keratosis, or there are clues pointing to cancer, the doctor will take a tissue sample (biopsy) for pathology examination, which is the standard that gives the most definite answer. Our principle is "diagnose correctly first, then remove": we do not burn or laser a mark that is not yet certain to be non-cancerous, because destroying the lesion makes it impossible to diagnose afterward.
Telling seborrheic keratosis apart from moles, small dark spots and skin cancer
Several kinds of brown marks on the skin look alike but carry very different risks.
Moles and small dark spots (melanocytic nevus) arise from pigment cells. They are usually smoother, evenly colored, and lack the stuck-on look or the blackhead-like openings of seborrheic keratosis.
Sun spots (solar lentigo) are purely flat patches, not thick or raised. In some people they are the starting point before developing into seborrheic keratosis.
Warts (viral wart) have a similarly rough surface but are caused by HPV, are contagious, and often have tiny bleeding dots under the surface.
Melanoma skin cancer is what needs the most caution. A seborrheic keratosis with uneven dark color can be hard to tell apart and requires dermoscopy and sometimes a biopsy.
Pigmented BCC and SCC sometimes disguise themselves as a rough mark resembling an irritated seborrheic keratosis, especially marks with a chronic sore or that bleed easily.
Warning signs: when to see a doctor promptly
A mark that grows unusually fast or clearly changes in size or shape
Uneven color, with several shades, unusually deep black, or color spreading beyond the edge
An asymmetric, irregular edge that is uneven
Bleeds easily, forms a sore, itches, or stays inflamed and never heals
Many new seborrheic keratoses appearing rapidly with itching. This is uncommon but is called the Leser-Trélat sign, and is sometimes associated with internal cancers (for example of the digestive system), so it should be evaluated thoroughly.
How to remove seborrheic keratosis in a way suited to Asian skin
Seborrheic keratosis does not need treatment because it is not dangerous. Removal is done for cosmetic reasons, to reduce friction and irritation, or when it may not be seborrheic keratosis. The doctor chooses a method according to the type, location, thickness and skin tone of the patient.
Freezing with liquid nitrogen (cryotherapy) suits thin, shallow marks, but care is needed in Asian skin because white patches (hypopigmentation) can become permanent if the freezing is too deep or too long.
Electrocautery and scraping (electrodesiccation and curettage) suits raised growths. It is done with local anesthetic, and depth can be well controlled.
Shave excision with biopsy (shave excision + biopsy) is used when pathology confirmation is wanted at the same time.
Resurfacing lasers (CO2 or Erbium laser) allow fine adjustment of depth and suit the face and large numbers of marks where a smooth finish is wanted.
Treating DPN commonly uses gentle electrocautery or laser, with a small test spot first to see how the skin color responds before treating everything, because the face in darker skin is at risk of dark marks.
What needs to be understood honestly is that every method carries a chance of post-inflammatory hyperpigmentation (PIH) in Asian skin, especially if done too deeply or aftercare is poor. Getting the depth right, strict sun protection, and applying medication as the doctor prescribes after the procedure are therefore very important. Even after complete removal, new seborrheic keratoses can still appear with age, so it is not a once-and-for-all treatment for life.
What not to do with seborrheic keratosis
Do not pick, peel or shave it off yourself, because of the risk of bleeding, infection and scarring, and if it is actually cancer the diagnosis will be missed.
Do not apply wart-removing solutions or strong acids yourself, especially on the face, because they burn the skin into sores and permanent dark marks.
Do not have it burned at places that are not medical facilities, because there is no diagnosis to rule out cancer and there is a risk of scarring from treating too deeply.
Aftercare and prevention
Apply sunscreen regularly. This helps slow new ones from forming and reduces dark marks after treatment.
Care for the wound as advised, avoid picking at scabs, and avoid strong sun while the wound heals.
Check your own skin from time to time, watch for marks that change, and have a doctor examine any mark you are unsure about before deciding to remove it.
Frequently asked questions (FAQ)
What causes seborrheic keratosis?
Seborrheic keratosis comes from an age-related increase in the number of epidermal skin cells, together with genetics and accumulated sun exposure. It is linked to non-dangerous mutations of genes in skin cells. It is not caused by clogged oil, poor hygiene or a virus, and it is not contagious.
Is seborrheic keratosis dangerous? Is it cancer?
Seborrheic keratosis is a benign growth and does not turn into cancer. However, some skin cancers, especially melanoma and pigmented BCC, can look similar. If a mark grows quickly, has uneven color, bleeds, or many new ones appear rapidly with itching, see a doctor to be sure.
How does seborrheic keratosis differ from a mole or small dark spot?
Seborrheic keratosis comes from cells in the upper layer of the skin. Its surface is rough and looks stuck on, and under the scope it often shows pearl-like cysts and blackhead-like openings. Moles and small dark spots come from pigment cells, and are smoother with even color. Skin scope examination helps tell them apart clearly.
Are small dark bumps on the cheeks (DPN) seborrheic keratosis? How are they treated?
Yes. DPN is a type of seborrheic keratosis that is common in people with darker skin, including Thai people. It is treated with gentle electrocautery or laser, and doctors usually try a small test spot first to see how the skin color responds, because the face in darker skin can develop dark marks after treatment.
Will removing seborrheic keratosis leave a scar or white patch?
When done by a doctor with appropriate depth control, the chance of scarring is low, but Asian skin may develop temporary dark marks, and freezing that is too deep can cause permanent white patches. The method therefore has to suit the skin tone, with good aftercare.
Will seborrheic keratosis come back after removal?
A mark that has been completely removed usually does not return in the same spot, but because seborrheic keratosis is related to age and genetics, new ones can keep appearing in other areas with age.
Written by Dr. Patara Voravutinon, Dermatologist · Last reviewed August 3, 2026
Comments