Section Editor: Allison Osmond MD FRCPC
June 18, 2026
Seborrheic keratosis is a very common, noncancerous (benign) skin growth. It develops from squamous cells, the flat cells that make up the epidermis (the outer layer of the skin). Seborrheic keratoses become more common with age, and many people develop several over time.
This article explains what a seborrheic keratosis is, what the findings in your pathology report describe, and why this growth is considered harmless. A seborrheic keratosis is benign, does not turn into cancer, and in most cases needs no treatment at all.
What causes a seborrheic keratosis?
The exact cause is not fully understood, but seborrheic keratoses become more common as people get older, and a tendency to develop them often runs in families. The cells in a seborrheic keratosis carry harmless genetic changes (most often in genes called FGFR3 and PIK3CA) that cause the squamous cells to grow into a thickened patch but do not make the growth cancerous. Long-term sun exposure may also play a role. Seborrheic keratoses are not contagious and are not caused by poor hygiene.
Rarely does a person develop many new seborrheic keratoses quite suddenly. This is called the sign of Leser-Trélat, and because it has occasionally been linked to an internal illness, it is worth mentioning to a doctor if it happens.
What are the symptoms of a seborrheic keratosis?
A seborrheic keratosis usually appears as a raised, bumpy, or waxy patch of skin that can be light tan, brown, or black. It is often described as looking “stuck on” to the skin. These growths range from a few millimeters to a couple of centimeters across, and many people have more than one. A seborrheic keratosis can look similar to a wart, a liver spot, or a mole, and it is usually painless, although it may become itchy or irritated if it catches on clothing or jewelry.
How is the diagnosis made?
A seborrheic keratosis can often be recognized by a doctor based on its appearance. When the growth is removed, because it is irritated, changing, or being checked to rule out skin cancer, the tissue is examined under the microscope by a pathologist after a shave, excisional biopsy, or excision.
Under the microscope, a seborrheic keratosis is composed of a thickened epidermis containing small, uniform squamous cells that appear orderly and similar to one another. Small, round spaces filled with keratin (the tough protein that forms the outer layer of skin), called horn cysts, are a characteristic feature. The pathologist examines the tissue carefully to confirm that the growth is benign and to ensure there is no sign of skin cancer, since a seborrheic keratosis can resemble other growths.
What are the types of seborrheic keratosis?
Pathologists divide seborrheic keratosis into several types, called variants, based on how the cells look under the microscope. All of them are benign. The most common include:
- Acanthotic — The epidermis is much thicker than in a usual seborrheic keratosis.
- Papillomatous — The surface cells grow in tall, finger-like projections.
- Adenoid (reticulated) — Thin strands of squamous cells extend into the deeper layers of the skin.
- Clonal — The squamous cells look very similar, as if grown from a single cell.
- Inverted follicular keratosis — The cells grow downward toward the dermis instead of up from the surface.
- Irritated (inflammatory) — Many immune cells are mixed in with the squamous cells.
- Lichenoid — A band of immune cells called lymphocytes is seen just beneath the squamous cells.
- Desmoplastic — This type can look like squamous cell carcinoma under the microscope but is still benign.
Can a seborrheic keratosis become cancer?
A seborrheic keratosis is benign and does not turn into skin cancer. However, a skin cancer such as melanoma or squamous cell carcinoma can occasionally look like a seborrheic keratosis or grow right next to one. This is the main reason a growth that changes, bleeds, or looks unusual is sometimes removed and examined under the microscope, so the pathologist can confirm it is harmless.
What happens after this diagnosis?
In most cases, a seborrheic keratosis needs no treatment and can simply be left in place. When a seborrheic keratosis is removed, it is usually for one of the following reasons: it is irritated or catches on clothing or jewelry; it is itchy or bleeds; it is cosmetically bothersome; or it needs to be examined to ensure it is not skin cancer. Common ways to remove a seborrheic keratosis include cryotherapy (freezing), curettage (scraping), and shave removal. If a growth is only partly removed, it can sometimes return, but this is not harmful. Whether or not a seborrheic keratosis is removed, it is reasonable to keep an eye on your skin and see a doctor if a growth changes.
Questions to ask your doctor
- Is my growth definitely a benign seborrheic keratosis?
- Was there any sign of skin cancer in or near it?
- Does it need to be removed, or can it be left alone?
- If I would like it removed, what are the options?
- Could it come back after removal?
- I have many of these growths. Is that anything to worry about?
- I developed several new ones quite suddenly. Should that be checked?
- What changes in growth should prompt me to see a doctor?
- How can I tell a harmless growth from one that needs checking?
Related articles
We are proud to partner with:
