Skin Health More Skin Conditions An Overview of Seborrheic Keratosis By Heather L. Brannon, MD Updated on April 15, 2023 Medically reviewed by Susan Bard, MD Print Table of Contents View All Table of Contents What They Are Causes Diagnosis Treatment 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. Some call seborrheic keratosis growths "the barnacles of aging," as they're most common after age 50. 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 solesAppear on their own or within groupsRange in size from a pinpoint to over an inch in diameterRest flat against the skin or are raisedLight tan to dark brown but may also be white, black, yellow, or greyRound in shapeWaxy 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. 20 Types of Skin Lesions and What They Look Like This photo contains content that some people may find graphic or disturbing. See Photo DermNet / CC BY-NC-ND This photo contains content that some people may find graphic or disturbing. See Photo DermNet / CC BY-NC-ND 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)RednessBleeding on or around seborrheic keratoses Skin Cancer 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. Seborrheic keratosis can be mistaken for: Common wart Precancerous lesion called actinic keratosis This photo contains content that some people may find graphic or disturbing. See Photo Viral warts on hand. DermNet / CC BY-NC-ND This photo contains content that some people may find graphic or disturbing. See Photo Actinic keratosis. DermNet / CC BY-NC-ND 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. Bone Marrow Biopsy: Purpose and Results 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. 9 Sources Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. Braun RP, Ludwig S, Marghoob AA. Differential diagnosis of seborrheic keratosis: clinical and dermoscopic features. J Drugs Dermatol: JDD. 2017;16(9):835-42. American Academy of Dermatology Association. Seborrheic keratoses: overview. American Academy of Dermatology Association. Seborrheic keratoses: signs and symptoms. Conic RZ, Napekoski K, Schuetz H, Piliang M, Bergfeld W, Atanaskova Mesinkovska N. The role of immunosuppression in squamous cell carcinomas arising in seborrheic keratosis. J Am Acad Dermatol. 2017;76(6):1146-1150. doi:10.1016/j.jaad.2016.12.002 Cimpean I, Theate I, Vanhooteghem O. Seborrheic keratosis evolution into squamous cell carcinoma: a truly modified sun-related tumor? A case report and review of the literature. Dermatol Reports. 2019;11(1):7999. doi:10.4081/dr.2019.7999 American Academy of Dermatology Association. Seborrheic keratoses: who gets and causes. Del rosso JQ. A closer look at seborrheic keratoses: patient perspectives, clinical relevance, medical necessity, and implications for management. J Clin Aesthet Dermatol. 2017;10(3):16-25. Wollina U. Seborrheic keratoses - the most common benign skin tumor of humans. Clinical presentation and an update on pathogenesis and treatment options. Open Access Maced J Med Sci. 2018;6(11):2270-2275. doi:10.3889/oamjms.2018.460 Gurel MS, Aral BB. Effectiveness of erbium: YAG laser and cryosurgery in seborrheic keratoses: Randomized, prospective intraindividual comparison study. J Dermatolog Treat. 2015;26(5):477-80. doi:10.3109/09546634.2015.1024597 Additional Reading Bedir R, Yurdakul C, Gucer H, Sehitoglu I. Basal cell carcinoma arising within seborrheic keratosis. J Clin Diagn Res. 2014;8(7):YD06-YD07. doi:10.7860/JCDR/2014/8665.4604 Boyd A, Su P, Shyr Y, et al. Squamous cell carcinomas in situ arising in seborrheic keratoses: an association with concomitant immunosuppression? Int J Dermatol. 2014;53(11):1346-50. doi:10.1111/ijd.12086 By Heather L. Brannon, MD Heather L. Brannon, MD, is a family practice physician in Mauldin, South Carolina. She has been in practice for over 20 years. See Our Editorial Process Meet Our Medical Expert Board Share Feedback Was this page helpful? Thanks for your feedback! What is your feedback? Other Helpful Report an Error Submit