Seborrheic keratoses are noncancerous growths on the skin. They can vary in color and typically appear on the back, shoulders, chest, or face.

Seborrheic keratoses can appear anywhere on the skin except the palms, soles, and mucous membranes. They are also known as basal cell papillomas or seborrheic warts.

Seborrheic keratoses can look like warts but are not warts. Warts result from a virus, such as the human papillomavirus (HPV). Seborrheic keratoses are unlikely to stem from HPV or another virus. They are not contagious.

They often appear on the scalp, trunk, neck, arms, and legs and sometimes occur on the face. Some look black but are actually very dark brown.

Some individuals may have just one, but it’s common for several to develop.

Seborrheic keratoses are very common. More than 80 million people in the United States have seborrheic keratoses. They can occur at any age but are most common after 50 years.

Seborrheic keratoses may look like warts, moles, or skin cancer.

They can have the following features:

  • Color: Tan, brown, yellow, gray, or skin-colored; some are very dark brown but may appear black.
  • Location: Commonly on the trunk, scalp, neck, limbs, and sometimes the face. They do not affect the soles or palms.
  • Texture: Can be “waxy” in appearance or rough and crusty.
  • Raised or not: Can look as if “stuck onto” the skin, but some are flat.
  • Size: Ranging from 1 millimeter (mm) to several centimeters in diameter.
  • Shape: Usually round or oval.
  • Sensation: Not painful but may itch or become irritated.
  • Number: Ranging from one to hundreds of lesions.
  • Growth: Lesions usually start as small, rough bumps and gradually get thicker and develop a warty surface. They grow slowly.

Some lesions can be light-colored and flat, like a solar lentigo, which is also known as a sunspot or “liver” spot.

On dark skin, seborrheic keratoses present similarly but are more likely to be the darker brown type.

Seborrheic keratosis lesions are rarely painful but can be annoying, depending on their position. It is important not to pick or scratch them as this can lead to bleeding, swelling, and, potentially, infection.

There are many types and subtypes of seborrheic keratoses, including stucco keratoses and dermatosis papulosa nigra.

Stucco keratoses are multiple small, light tan papules or bumps with a rough texture, specifically around the lower legs and ankles.

Dermatosis papulosa nigra appears as multiple small, dark-pigmented papules or bumps. Lesions often appear on the face. They tend to affect people with medium or dark skin.

Other subtypes include hyperkeratotic keratosis, which causes the skin to thicken.

It can be difficult to distinguish between seborrheic keratoses and skin cancer lesions. For this reason, anyone who notices new lesions or skin changes should visit a doctor.

If a person already has a diagnosis of seborrheic keratoses, they should request an appointment if the following occurs:

  • a large number of growths grow in a short space of time
  • the borders around the growths are irregular or blurred
  • the growths are irritated by clothes or regularly bleed (removal may be an option)
  • growths or sores develop and do not heal
  • the growths are an unusual color, such as purple, reddish black, or blue
  • there is itching or irritation

People with multiple seborrheic keratoses may wish to make a yearly appointment with a dermatologist to check for changes that could be cancerous.

How do you know if a lesion is cancerous?

In most cases of seborrheic keratosis, no treatment is necessary.

However, a doctor may recommend removing the growth in the following cases:

  • It is hard to distinguish from skin cancer or the diagnosis is uncertain.
  • The individual does not like it and wants to remove it.
  • It causes itching or irritation, or clothing and jewelry rub against it.

If a dermatologist carries out a biopsy, they will usually remove the seborrheic keratosis at the same time.

There are several ways to remove seborrheic keratoses.

Cryosurgery

A doctor applies liquid nitrogen to the growth with a spray gun or cotton swab. The lesion freezes and falls off in a few days. A blister may form that eventually dries into a crust and falls off.

However, the lesion can grow back, and changes in pigmentation can also occur.

How can cryosurgery treat a wart?

Skin shaving (shave excision)

A doctor shaves off the lesion with a scalpel without touching the layers beneath the skin’s surface. The collected cells can then go to a laboratory for a biopsy.

Electrocautery, curettage, or both

In electrocautery, also known as electrosurgery, a surgeon uses an electric current to burn (cauterize) the growth. They administer a local anesthetic to limit any pain.

In curettage, a doctor uses a curette, a scoop-shaped surgical instrument, to scrape off the growth. A local anesthetic to numb the area is typically applied as well.

Some people need only electrocautery, some need curettage, and others need both.

Laser therapy

A doctor uses a laser to remove the lesion.

Laser treatment can be ablative or nonablative.

Ablative surgery removes the epidermal and superficial layers of skin and heats the underlying layer to stimulate the growth of new collagen fibers.

Nonablative surgery is less invasive. It works by creating heat in the skin without injuring the surface of the skin and stimulates the growth of new collagen.

Topical treatments

Researchers are currently looking into options for topical applications to remove seborrheic keratoses.

The Food and Drug Administration (FDA) has approved a 40% hydrogen peroxide solution for raised keratoses that appears safe and effective. Minor adverse effects may occur, such as scaling, inflammation, and changes in skin color.

Chemical peels are also available. A doctor applies a peel containing trichloroacetic acid to the lesion.

All these methods have disadvantages, such as:

  • irritation and discomfort in the area during recovery time
  • changes in pigmentation, where the skin becomes lighter or darker
  • the need for several sessions, as a doctor may be unable to remove all lesions in one session
  • recurrence of growths or lesions continue to appear in other areas

There are no proven home remedies for seborrheic keratoses.

Lemon juice or vinegar can irritate the skin, possibly causing the lesion to dry and crumble. However, there is no evidence that this is safe or effective.

Some substances, such as tea tree oil, can trigger allergic contact dermatitis. This is an immune system reaction that causes itching and inflammation around the site.

Anyone with concerns about a lesion should talk with a doctor. They can check that it is not melanoma and advise on treatment, if appropriate.

Dermatologists are not certain why seborrheic keratoses develop.

Possible causes and risk factors include:

  • Skin damage: Some types of seborrheic keratoses appear after dermatitis or sunburn.
  • Genetic factors: A genetic mutation could be responsible when people develop a high number of seborrheic keratoses or when the condition runs in families.
  • Age: They are more common in people 50 years old and older.
  • Exposure to UV light: Similarities with solar lentigo suggest UV light may play a role.
  • Medication: People who use epidermal growth factor receptor inhibitors to treat cancer may have a higher risk of warty growths.
  • Skin friction: This may increase the risk and explain why they often appear in skin folds.

To diagnose seborrheic keratosis, a primary care doctor or dermatologist:

  • asks about symptoms and family and medical history
  • does a visual and physical examination
  • may recommend a biopsy to rule out skin cancer and remove a growth at the same time
  • may recommend further tests to rule out other conditions

Seborrheic keratoses are not cancerous, but they can share some features with malignant lesions.

Since it can be hard to distinguish between skin cancer and seborrheic keratoses, it is best to check with a doctor, especially if multiple lesions appear in a short time or if lesions change.

If the doctor suspects melanoma or is unsure, they may recommend a biopsy for examination under a microscope.

Anyone with a large number of seborrheic keratoses requires careful screening, as there is an increased chance of missing any cancerous lesions.

Researchers believe the gene process used by the lesions could help scientists learn more about certain types of cancer.

Here are some answers to questions people often ask about seborrheic keratoses.

How do you get rid of seborrheic keratoses?

In most cases, seborrheic keratoses do not need treatment, but a person may opt to remove them if they snag on clothing or jewelry, or they simply want them removed.

A doctor may remove one while taking a biopsy for skin cancer. Options include minor surgery, laser therapy, and cryotherapy. A doctor can advise on the best approach.

What do seborrheic keratoses look like?

Seborrheic keratoses can be skin-colored, tan, brown, yellow, gray, or very dark brown that may appear black. They can look waxy or rough, like a wart. Some are raised, as if stuck onto the skin, while others are flat.

Seborrheic keratoses can range from 1 mm to several centimeters across. They usually grow slowly.

Are seborrheic keratoses serious?

Seborrheic keratoses are not cancerous but can share some features with malignant lesions. They can be hard to tell apart from skin cancer, so it is essential to visit a doctor about any new or unexplained lesions.

Seborrheic keratoses are harmless lesions that appear on the skin, especially as people get older. They can occur anywhere on the body except the soles and palms.

They may be yellow, brown, tan, or skin-colored. Some look black but are actually dark brown. They may be raised, as if stuck onto the skin, but some are flat.

It can be hard to tell the difference between seborrheic keratoses and skin cancer. For this reason, a person should visit a doctor if they notice a new lesion or if a lesion changes in any way.