An Overview of Seborrheic Keratosis

Seborrheic keratosis is a dermatologic condition characterized by wart-like growths that may appear anywhere on the skin, except a person's palms and soles. Seborrheic keratoses can vary in appearance, but are typically light tan to dark brown, round, and have a waxy or warty stuck-on-the-skin appearance. While they are harmless, some seek treatment for aesthetic purposes and because the growths can become irritated or get caught on clothes and jewelry.

The growths develop in a type of skin cell known as a keratinocyte, which is on the outermost layer of skin (epidermis). While most dermatologists are able to diagnose seborrheic keratosis by appearance alone, a skin biopsy may be performed to rule out worrisome mimicking skin conditions like skin cancer.

Seborrheic keratosis is a non-cancerous skin growth that has the following typical characteristics:

• Rests flat against the skin or is raised
• Starts off as a small, round bump that then thickens and develops a waxy or wart-like appearance (although in some cases, the surface is smooth)
• Brown in color, but may also be white, black, yellow, or grey
• Develops anywhere on the skin (e.g., chest, back, face, and neck), but not on the palms and soles
• Appears on its own or within groups
• Ranges in size from a pinpoint to over an inch in diameter

Because only the top skin layer is involved, seborrheic keratosis often has a "pasted-on" appearance, similar to a barnacle. The number of growths typically increases as a person ages.

Seborrheic keratoses are not painful but may itch, especially as a person gets older. If scratched or picked at, the growths can become irritated.

While seborrheic keratosis is considered a benign skin condition, in rare cases, skin cancer (e.g., squamous cell carcinoma or basal cell carcinoma) can arise from cells that are contained with seborrheic keratosis.

Research suggests that people with a suppressed immune system may be at a more increased risk for this phenomenon, which is called a malignant or cancerous transformation of a seborrheic keratosis.

This is why careful observation of these growths by a dermatologist is important, especially if atypical signs are present, such as:

• Ulceration (sores)
• Excoriations (scratch marks)
• Redness
• Bleeding on or around seborrheic keratoses

The precise cause of seborrheic keratosis remains unknown. Experts believe genes play a role, as these growths tend to run in families.

Besides genetics, other factors that may increase a person's chances for developing seborrheic keratoses include:

• Sunlight exposure
• Chronic friction (this may be why seborrheic keratoses develop in skin folds)
• Exposure to viruses, specifically the human papillomavirus (HPV), although this theory has lost a lot of favor over the years

A dermatologist can usually diagnose seborrheic keratosis simply by its outright appearance or by using a lighted instrument called a dermatoscope.

However, in some instances, if the growth looks suspicious for skin cancer (or there is really any doubt about what the growths are), a skin biopsy will be performed to confirm a diagnosis.

The different types of skin biopsies that may be performed include:

• Shave biopsy, in which the lesion is shaved to remove a tissue sample
• Punch biopsy: A hole-punch-type device removes a narrow cylinder of tissue
• Excisional biopsy (using a scalpel and sutures)

Skin samples are examined under a microscope by a doctor called a pathologist.

If cancer cells are found, additional testing will be needed to determine the stage of the cancer, which will guide treatment.

Seborrheic keratosis is typically not treated unless a person considers the growth to be cosmetically undesirable, uncomfortably itchy, or easily irritated.

The good news is that there are several different treatment options available:

• Cryotherapy with liquid nitrogen: A procedure in which a dermatologist applies liquid nitrogen (an extremely cold liquid) to freeze off the growth.
• Shave excision: A procedure that involves using a sterile razor and a local anesthetic (a numbing agent) to shave off the growth.
• Curettage: A procedure in which an instrument called a curette is used to scoop out the growth from the skin.
• Electrocautery: A procedure in which tissue is burned with an electrical current after a local anesthetic is applied. Sometimes electrocautery is combined with curettage or shave excision.
• Chemical peel: A therapy that involves applying a solution such as trichloroacetic acid to the seborrheic keratosis so that it peels off on its own (chemical peels work by removing the outer layers of the skin).
• Ablative laser treatment: A laser is directed toward the affected skin to remove the seborrheic keratoses.

Seborrheic keratosis can sometimes be difficult to distinguish from skin cancer, especially when it first appears. This is why it's important to not make assumptions about any new spots, patches, or growths that develop on your skin. Instead, be proactive by seeing a dermatologist for a proper diagnosis and treatment plan.