A seborrheic keratosis is a type of skin growth.

The term keratosis refers to a knobby overgrowth of keratinocytes. The keratinocyte is the most common type of skin cell in the epidermis (the outer layer of the skin).

Older or less common names for this condition include:

  • barnacles of aging
  • basal cell papillomas
  • brown warts
  • seborrheic warts
  • senile warts
  • wisdom warts

The growths aren’t harmful. However, in some cases, a seborrheic keratosis can be difficult to distinguish from melanoma, a very serious type of skin cancer.

Seborrheic keratosis affects about 83 million people in the United States, according to a 2015 study.

According to the British Association of Dermatologists, 30 percent of people in the United Kingdom will have a seborrheic keratosis by age 40. By 70 years old, 75 percent of people will have one.

If your skin changes unexpectedly, you should always have it looked at by a doctor or dermatologist.

What does seborrheic keratosis look like?

A seborrheic keratosis is usually easily identified by appearance.

Location

Multiple lesions may appear, although at the beginning there might be just one. Growths can be found anywhere on the body except the soles of the feet, palms, and mucous membranes. Some places they may show up include the:

  • scalp
  • face
  • chest
  • shoulders
  • abdomen
  • back

A sudden increase in the number and size of seborrheic keratoses may indicate the presence of the Leser-Trélat sign, which is rare. The cause of the Leser-Trélat sign is unknown, but it may be associated with stomach, colon, or skin cancer. Experts are unclear on whether it’s a symptom of the cancer or a separate skin disorder.

Texture

Growths often start out as small, rough areas. Over time, they tend to develop a thick, wart-like surface. They’re frequently described as having a “stuck-on” appearance. They may also look waxy and have slightly raised surfaces.

Shape

Growths are usually round or oval-shaped.

Color

Growths are usually brown, but they can also be yellow, white, or black.

Seborrheic keratosis vs. actinic keratosis

Actinic keratosis, another type of skin growth, isn‘t the same as seborrheic keratosis. An actinic keratosis is a rough skin patch that usually develops in areas of the skin that receive a lot of sun exposure. Unlike a seborrheic keratosis, it‘s considered precancerous.

An actinic keratosis is also called a solar keratosis.

A seborrheic keratosis usually causes no symptoms. However, for some people it may:

  • be itchy
  • become irritated, although it usually isn‘t painful
  • catch on clothing, depending on its location

In many cases, a seborrheic keratosis doesn’t need treatment. However, a healthcare professional may decide to remove any growths that have a suspicious appearance or cause physical or emotional discomfort. A doctor, dermatologist, or — in some cases — a physician assistant will perform your procedure.

Treatment and removal methods for a seborrheic keratosis include the following:

  • Cryosurgery. Cryosurgery uses liquid nitrogen to freeze off the growth.
  • Electrosurgery. In electrosurgery, a healthcare professional uses an electrical current to scrape off the growth. The area is numbed before the procedure.
  • Curettage. In curettage, a healthcare professional scrapes off the growth with a curette, a scoop-like surgical instrument. Curettage is sometimes combined with electrosurgery.
  • Shave excision. Shave excision is similar to curettage. A healthcare professional may perform it if they want to send a sample of the growth to a lab for analysis.
  • Ablation. This procedure uses a special laser to vaporize the growth.
  • Hydrogen peroxide solution. The Food and Drug Administration (FDA) has approved a 40 percent hydrogen peroxide solution (Eskata) to destroy seborrheic keratosis cells. It’s only available by prescription. However, this method often causes skin irritation, according to a 2019 report.
  • Nitric acid-zinc solution. The topical solution Nitrizinc Complex contains nitric acids, zinc, copper salts, and organic acids. A small 2019 study found this method to be safe and effective at shrinking or completely eliminating most lesions within a 6-month period.

To prevent bleeding, inflammation, or infection, it’s important to not try to remove a seborrheic keratosis yourself by picking or scratching at it.

After the seborrheic keratosis is professionally removed, your skin may be lighter at the site of removal. The difference in skin color often becomes less noticeable over time.

Most of the time a seborrheic keratosis won’t return, but it’s possible to develop a new one on another part of your body.

Experts don’t know what causes a seborrheic keratosis to develop. They aren‘t bacterial, viral, or contagious.

The following risk factors may make you more likely to develop a seborrheic keratosis:

  • Older age. The condition often develops in those who are in their 30s or 40s, and risk increases with age. It isn‘t common in people younger than 20 years old.
  • Having family members with seborrheic keratosis. This skin condition appears to run in families, and it can often be inherited. Risk increases with the number of affected biological relatives.
  • Pregnancy or hormone therapy. Seborrheic keratoses may develop during pregnancy. These growths may also develop while a person undergoes estrogen replacement therapy.
  • Frequent sun exposure. Researchers in South Korea found that one subtype of seborrheic keratosis, the adenoid type, occurred more often in sun-exposed skin than protected skin. However, seborrheic keratoses can also appear on skin that’s usually covered up outdoors.
  • Having lighter skin. Seborrheic keratoses are generally more common in people with light skin, although people with darker skin can develop them too.
Did you know?

Some experts believe that dermatosis papulosa nigra, a skin condition that’s more common in people with darker skin, may be a subtype of seborrheic keratosis. Other experts think that dermatosis papulosa nigra is a distinct condition.

A dermatologist will often be able to diagnose seborrheic keratosis by eye. If there’s any uncertainty, they’ll likely remove part or all of the growth for testing in a laboratory. This is called a skin biopsy.

The sample from the biopsy will be examined under a microscope by a trained pathologist. This step can help a doctor or dermatologist diagnose the growth as either seborrheic keratosis or something else.

A seborrheic keratosis isn’t dangerous, but you shouldn’t ignore growths on your skin. It can be difficult to distinguish between harmless and dangerous growths. Something that looks like seborrheic keratosis could actually be melanoma.

Have a healthcare professional check your skin if:

  • There’s a new growth.
  • There’s a change in the appearance of an existing growth.
  • There’s only one growth (seborrheic keratosis usually exists as several).
  • A growth has an unusual color, such as purple, blue, or reddish-black.
  • A growth has borders that are blurred, jagged, or otherwise irregular.
  • A growth is irritated or painful.

If you’re worried about any growth, make an appointment with a doctor or dermatologist. It’s better to be too cautious than ignore a potentially serious problem.