Seborrheic keratosis is the most common type of benign skin lesion. About 80 million Americans have one or more of these non-cancerous growths on their skin.

Seborrheic keratosis growths can appear anywhere on your body, but they most commonly arise on sun-exposed areas of your skin, such as the face, head, neck, chest, back, arms, or legs. These spots can vary in size, from about the size of a pencil eraser to the size of a quarter (about an inch) or even larger.

Although they can affect teenagers or young adults, the growths are most common among adults aged 50 and older. They occur more frequently with age; more than 90% of adults aged 65 and older are believed to have at least one seborrheic keratosis. Men and women are affected equally.

Importantly, seborrheic keratosis is a benign condition; the growths do not become cancerous and therefore do not require treatment. However, some people opt to have the spots removed for cosmetic reasons or if the spots become irritated or inflamed because of their location and/or trauma.

Seborrheic keratosis is a type of benign (non-cancerous) skin tumor or growth. These slow-growing spots are typically raised and sometimes have a rough texture. Some look similar to warts. They also vary in number; some people have a single seborrheic keratosis, while others have several, dozens, or even hundreds of spots on their skin. These growths are neither viral or bacterial and, therefore, cannot spread.

Seborrheic keratosis occurs when skin cells, known as keratinocytes, multiply rapidly, resulting in a non-cancerous growth. This can occur in people with a family history of the condition, or it may affect people who have spent a significant amount of time in the sun.

In rare instances, a person can suddenly develop a significant number of seborrheic keratosis growths. Although exceedingly rare, this may signal what’s known as the “Leser-Trélat sign,” which indicates that a person might have gastrointestinal cancer, lung cancer, lymphoma, or leukemia. Anyone thought to have the Leser-Trélat sign should see a specialist who can diagnose cancer. However, it’s important to know that the Leser-Trélat sign is very uncommon and the vast majority of seborrheic keratosis growths are slow-growing and benign.

Doctors aren’t sure what causes seborrheic keratosis, but there is very likely a genetic component—certain genetic mutations have been linked to the condition. Sun exposure and changes in estrogen levels have also been linked to seborrheic keratosis.

Possible causes of seborrheic keratosis include:

• A family history of seborrheic keratosis
• Fibroblast growth factor receptor 3 (FGFR3) genetic mutation
• PIK3CA genetic mutation
• Pregnancy
• Hormone therapy

People with seborrheic keratosis may notice a spot or spots on their skin that:

• Look white, flesh-colored, yellow, pink, tan, brown, gray, or black
• Are round or oval-shaped
• Have a raised surface
• Have a velvety- or waxy-looking surface
• Have a rough- or crusty-looking texture
• Have a surface texture similar to that of a wart
• Appear in groups or clusters
• Have a uniform appearance

Sometimes, the spots on the skin can also:

• Feel itchy
• Become irritated
• Appear red or inflamed
  
• Bleed

People are more likely to develop seborrheic keratosis if they:

• Are age 50 or older
• Have spent a significant amount of time sunbathing or with the skin exposed to the sun
• Have a family history of seborrheic keratosis
• Have an FGFR3 genetic mutation
• Have a PIK3CA genetic mutation
• Are pregnant
• Have taken hormone therapy

Although these growths appear most often on people with fair skin, those with darker skin can also develop the condition. In people with darker skin, growths often appear on the upper cheeks, just beneath the eyes in what is often referred to as “dermatosis papulosa nigra.”

A dermatologist typically diagnoses seborrheic keratosis. The growths are usually discovered during a physical examination, then confirmed with a biopsy when needed. Doctors will use information from your medical history to make a diagnosis.

During a discussion of your medical history, tell your doctor if seborrheic keratosis runs in your family, if you’ve spent a considerable amount of time in the sun, and if you are pregnant or taking hormone therapy.

During a physical exam, your doctor will look for seborrheic keratosis by using a dermatoscope. This tool provides magnification and a glare-free light source, which allows for a more precise view of an area of skin.

Some cancerous conditions, including basal cell carcinoma and melanoma, can appear similar to certain seborrheic keratosis growths. For this reason, a growth may be biopsied to rule out a more serious condition. (Biopsy is the standard diagnostic test used to confirm the presence of seborrheic keratosis. Doctors will shave or scrape off skin cells from the growth and send them to a lab for analysis.)

In most cases, no treatment is necessary for seborrheic keratosis. Sometimes, the growths are removed because their location leads to chronic irritation or bleeding. Other times, people choose to have them removed for cosmetic reasons.

When a seborrheic keratosis is removed, options include:

• Cryotherapy, in which a growth is “frozen off” the body
• Electrosurgery, in which an electrical current is applied to the growth to remove it
• Curettage, in which a special surgical tool is used to scrape the growth off the skin; Electrosurgery plus curettage is used in some cases
• Laser treatment, in which light from a laser destroys the growth
• Dermabrasion, in which a skin-resurfacing tool is applied to the skin to smooth away growths
• Shaving or snipping off the growth with special tools

Seborrheic keratosis should not affect a person’s overall health, unless it is identified as seborrheic keratosis due to the Leser-Trélat sign. In that case, the person may need treatment for non-skin cancer, such as lymphoma or cancer of the gastrointestinal tract. However, the skin growths themselves should not affect an individual’s prognosis.

“Yale Dermatology faculty are well-trained experts in recognizing seborrheic keratosis, and guiding patients through the decision-making process, whether or not a seborrheic keratosis needs further treatment,” says Yale Medicine dermatologist Christopher Bunick, MD, PhD. “In general, if a seborrheic keratosis is symptomatic to the patient in any way, it might need treatment. Importantly, an expert skin exam from a dermatologist can alleviate patient concerns about whether a particular lesion is cancerous or not. Early recognition and treatment, if needed, can provide patients with an optimal health outcome.”