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Seborrhoeic keratosis is a common, benign skin growth associated with aging that can resemble skin cancer. An overview of its causes, appearance, and treatment.
A seborrhoeic keratosis is a benign, non-cancerous growth that appears on the skin with advancing age. Often abbreviated to SK, these warty, sharply defined lesions are among the most common skin growths encountered in adult dermatology, and they affect people of every skin type and background. Although a seborrhoeic keratosis is entirely harmless, its colour, surface texture, and occasionally irregular outline can closely resemble a skin cancer, which is a frequent source of patient concern and a common reason for dermatological assessment.
Understanding what a seborrhoeic keratosis is, how it differs from more serious lesions, and which treatment options exist can help patients distinguish ordinary age-related changes from growths that genuinely warrant evaluation. The overview below summarizes the current understanding of these lesions, from their underlying biology to the methods used to remove them when removal is desired.
Seborrhoeic keratoses are remarkably prevalent, particularly among older adults. Population studies indicate that more than 90% of people over the age of 60 have at least one such lesion, and the number of growths tends to increase with advancing age [1][2]. Although individual lesions can begin to appear in the third or fourth decade of life, seborrhoeic keratoses are uncommon before the age of 20.
The condition is recognized under several historical names, including basal cell papilloma, senile wart, wisdom wart, and barnacle. A seborrhoeic keratosis belongs to a broader family of benign keratoses, a category that also includes the flat, pigmented patch known as a solar lentigo and the inflamed variant called a lichen planus-like keratosis. These related lesions share a non-cancerous nature and a comparable association with skin aging.
The precise cause of seborrhoeic keratoses is not fully understood. Despite the name, these growths are not related to sebum, sebaceous gland activity, or seborrhoeic dermatitis; the shared terminology reflects an outdated assumption rather than a genuine biological link. Seborrhoeic keratoses are instead regarded as a degenerative change within the epidermis that becomes more frequent over time.
A genetic tendency appears to play a substantial role. Some individuals inherit a predisposition to develop large numbers of lesions, and stable, non-inherited mutations are commonly found within the growths themselves. Activating mutations in the fibroblast growth factor receptor 3 gene, known as FGFR3, are frequently detected in seborrhoeic keratoses and are present even in early, flat lesions [3]. Mutations in the PIK3CA gene, which helps regulate cell growth and survival, are identified in a smaller proportion of lesions [4]. Because such mutations accumulate with age and sun exposure, ultraviolet radiation and cumulative skin trauma, such as friction within body folds, are considered contributing factors.
In the overwhelming majority of cases, seborrhoeic keratoses remain isolated and benign. Rarely, the sudden eruption of numerous new lesions over a short period, often accompanied by itching, has been associated with an underlying internal cancer. This uncommon association is referred to as the sign of Leser-Trelat, and when it is suspected, a thorough evaluation for an occult malignancy is warranted [5].
Seborrhoeic keratoses vary widely in size, colour, and texture, which is part of what makes them visually distinctive. A classic lesion has a sharply demarcated border and a surface that appears to sit on top of the skin, an effect frequently compared to a barnacle attached to the hull of a ship. Lesions may occur singly or in large numbers and can develop almost anywhere on the body, with the notable exception of the palms, soles, and mucous membranes.
Although most seborrhoeic keratoses cause no symptoms, lesions in areas of friction can become irritated, inflamed, itchy, or crusted, particularly when caught on clothing or jewellery. An irritated lesion may appear redder and more swollen than usual, which can occasionally heighten concern about its nature.
Dermatologists recognize several clinical and microscopic variants of seborrhoeic keratosis, each with characteristic features.
Solar lentigo. A flat, uniformly pigmented patch that develops in sun-exposed areas such as the face, hands, and shoulders. It is considered an early or closely related lesion that can gradually thicken into a raised seborrhoeic keratosis over time.
Stucco keratosis. Small, dry, greyish-white papules that typically appear on the lower legs, ankles, and the tops of the feet, often in clusters.
Dermatosis papulosa nigra. Numerous small, darkly pigmented papules that arise on the cheeks and upper trunk, most commonly in individuals with richly pigmented skin and frequently following a familial pattern.
Lichen planus-like keratosis. An inflamed variant in which the immune system reacts against the lesion. This inflammatory process can cause the growth to become red and irritated and may ultimately lead to its spontaneous disappearance.
Melanoacanthoma. A heavily pigmented form that contains an increased number of pigment-producing cells, giving it a particularly dark appearance that can mimic a melanocytic lesion.
In most situations, a seborrhoeic keratosis can be identified by visual examination alone, based on its characteristic stuck-on appearance and sharply defined border. When the diagnosis is less certain, a dermatologist may use dermoscopy, a non-invasive technique that magnifies the skin surface and reveals internal structures not visible to the naked eye.
Under dermoscopy, seborrhoeic keratoses commonly display distinctive features, including multiple round, whitish structures called milia-like cysts, dark plugs known as comedo-like openings, and a network of ridges and furrows that produces a brain-like, or cerebriform, pattern [6]. These clues help separate a benign growth from a malignancy.
Because pigmented or irritated lesions can occasionally resemble skin cancers such as basal cell carcinoma, squamous cell carcinoma, or melanoma, careful assessment is important. If uncertainty remains after clinical and dermoscopic examination, a skin biopsy, such as a shave, punch, or excisional sample, may be taken so that the tissue can be examined under a microscope to confirm the diagnosis [2].
Because seborrhoeic keratoses are benign, treatment is not medically necessary in most cases. Removal is generally considered when a lesion is cosmetically bothersome, repeatedly catches on clothing, or becomes persistently itchy or irritated, and occasionally to allow microscopic confirmation when the diagnosis is uncertain. Several effective removal methods are available, and the most appropriate option depends on the size, location, and number of lesions [2].
Cryotherapy. The application of liquid nitrogen freezes and destroys the lesion. This approach works well for thinner growths but may require more than one session and can occasionally cause temporary lightening or darkening of the treated skin.
Curettage and electrocautery. The growth is scraped away with a curette, and electrosurgery is then used to apply heat that controls bleeding and removes any remaining tissue. This combination is well suited to raised lesions. In a randomized comparison, curettage and cryotherapy were both effective, with similar cosmetic outcomes [7].
Laser treatment. Ablative lasers can vaporize a lesion with a high degree of precision, which is useful for growths in cosmetically sensitive areas.
Shave excision. The lesion is removed at the level of the surrounding skin with a surgical blade, a technique that also yields a tissue sample for examination when needed.
Chemical peel. A focused application of trichloroacetic acid, sometimes performed as part of chemical resurfacing, can remove selected superficial lesions.
Topical hydrogen peroxide. A high-concentration hydrogen peroxide solution, applied in a controlled clinical setting, has been approved specifically for raised seborrhoeic keratoses. Randomized controlled trials have shown that this non-invasive treatment can clear lesions, although more than one application is often required [8].
Every removal method carries potential drawbacks, the most notable being a change in skin pigmentation at the treated site, which is more likely in individuals with darker skin tones. No single technique can efficiently remove a large number of lesions in a single session, so a treatment plan is usually tailored to the individual.
Once they appear, seborrhoeic keratoses tend to persist indefinitely, and new lesions may continue to develop with age. Some growths, particularly those that become inflamed through the lichen planus-like process, may regress on their own, but spontaneous disappearance cannot be relied upon. Because the underlying cause is not fully understood, no proven method exists to prevent these lesions from forming, although consistent sun protection supports overall skin health and may reduce the development of related sun-induced growths.
The most important consideration is accurate diagnosis. Any growth that changes in size, shape, or colour, bleeds without clear cause, or simply looks different from a person's other lesions should be assessed by a physician, because these features can also occur in skin cancer. A dermatological evaluation, which may include dermoscopy or skin cancer screening, can confirm that a lesion is a harmless seborrhoeic keratosis and guide appropriate management. Patients who are uncertain about a new or changing skin growth are encouraged to arrange a consultation for professional assessment.
This article is intended for educational purposes and does not replace professional medical advice. Please consult your dermatologist for personalized recommendations.
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