An Overview of Seborrheic Keratosis

Skin barnacles, medically known as seborrheic keratoses, are wart-like growths that may appear anywhere on the skin except for the palms and soles. These growths are harmless, but you may want to have them removed for aesthetic reasons or because they are a source of irritation.

This article looks at seborrheic keratoses, what they are, and how they are diagnosed and treated.

What Are Skin Barnacles?

Seborrheic keratoses are harmless, noncancerous growths that usually appear during adulthood. These growths can vary in appearance but typically:

• Start off as small, round bumps that thicken and develop a waxy or wart-like appearance (although in some cases, the surface is smooth)
• Develop anywhere on the skin (e.g., chest, back, face, and neck), but not on the palms and soles
• Appear on their own or within groups
• Range in size from a pinpoint to over an inch in diameter
• Rest flat against the skin or are raised
• Light tan to dark brown but may also be white, black, yellow, or grey
• Round in shape
• Waxy or warty

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 you age.

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

Skin barnacles don't usually need to be treated, but some people have them removed for aesthetic purposes or because they can become irritated or get caught on clothes and jewelry.

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This photo contains content that some people may find graphic or disturbing.

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Presence of Other Symptoms

Seborrheic keratoses develop in a type of skin cell called a keratinocyte on the outermost layer of skin (epidermis). While most dermatologists can diagnose them by appearance alone, they may perform a skin biopsy to rule out worrisome conditions like skin cancer.

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 within a seborrheic keratosis.

Research suggests that people with a suppressed immune system may have an increased risk of 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

What Causes Skin Barnacles?

The precise cause of seborrheic keratosis remains unknown. Experts believe genes play a role, as these growths tend to run in families. Other factors that may increase your chances of developing them include:

• Sunlight exposure
• Chronic friction (such as inside skin folds)
• Exposure to viruses, specifically the human papillomavirus (HPV), although this theory has lost a lot of favor over the years

Diagnosis

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's any doubt about what they are, a skin biopsy can confirm a diagnosis.

This photo contains content that some people may find graphic or disturbing.

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This photo contains content that some people may find graphic or disturbing.

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

• Shave biopsy: The lesion is shaved to remove a tissue sample.
• Punch biopsy: A hole-punch-type device removes a narrow cylinder of tissue.
• Excisional biopsy: The entire lesion is removed with a scalpel.

A pathologist then examines the skin samples under a microscope. If they find cancer cells, you'll need additional testing to determine the stage of the cancer, which will guide treatment.

Treatment

Seborrheic keratosis doesn't typically need treatment unless you consider it cosmetically undesirable, it's uncomfortably itchy, or it's easily irritated.

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

• Cryotherapy with liquid nitrogen: The growth is frozen off with liquid nitrogen (an extremely cold liquid)
• Shave excision: It's removed with a sterile razor
• Curettage: It's scooped out with an instrument called a curette
• Electrocautery: The tissue is burned with an electrical current
• Chemical peel: A solution such as trichloroacetic acid causes the growth to slough off
• Ablative laser treatment: A laser removes the layer of skin

Research suggests that laser therapy is a better alternative than cryotherapy, as it's less likely to cause hyperpigmentation (when removal of the growth causes darkening of the skin).

Summary

Seborrheic keratoses are also called "skin barnacles." They tend to form during adulthood and are typically brown in color with a "stuck-on" appearance. These lesions are usually harmless, but you may want to have them removed for aesthetic reasons.

Because skin barnacles can sometimes look suspicious, your dermatologist may want to perform a biopsy to make sure the lesion is not cancerous. 

If you decide to have your seborrheic keratosis removed, your dermatologist can use a number of techniques including cryotherapy, a chemical peel, or laser treatment.

A Word From Verywell

A seborrheic keratosis can sometimes be difficult to distinguish from skin cancer, especially when it first appears. It's important to not make assumptions about any new spots, patches, or growths that develop on your skin. Be proactive and see a dermatologist for a proper diagnosis and treatment plan.