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# Seborrheic keratosis

Seborrheic keratoses are very common, harmless brown 'stuck-on' skin growths that appear with age. They are not cancer and are not contagious.

Updated 2026-11-01

## Structures involved

Tap one to see what it is and open it in 3D.

- [Skin](https://durgical.com/en/anatomy/skin/)
- [Stomach](https://durgical.com/en/anatomy/stomach/)

## Why it happens

- [Benign vs malignant tumours: the comparison table](https://durgical.com/en/general-pathology/benign-vs-malignant-tumours-the-comparison-table/)
- [Paraneoplastic syndromes: the table to know](https://durgical.com/en/general-pathology/paraneoplastic-syndromes-the-table-to-know/)
- [Skin: epidermis layers, dermis, hypodermis](https://durgical.com/en/histology/skin-epidermis-layers-dermis-hypodermis/)

## What it is

The most common benign epidermal tumour: a proliferation of keratinocytes that forms a well-defined, waxy, 'stuck-on' papule or plaque, tan to black, usually on the trunk, face or neck of middle-aged and older adults.

## Who gets it

Extremely common after age 40–50; most older adults have at least one, and numbers increase with age. Found in all skin types; in darker skin (frequent in Colombia) small dark facial papules called dermatosis papulosa nigra are a variant.

## Causes

- Benign clonal proliferation of epidermal keratinocytes
- Activating mutations in genes such as FGFR3 and PIK3CA in many lesions
- Ageing and family tendency; sun exposure may contribute to some types

## Risk factors

- Age over 40 years
- Family history of many seborrheic keratoses
- Sun-exposed skin for some variants
- Darker skin type for dermatosis papulosa nigra

## Pathophysiology

Somatic activating mutations in growth signalling pathways cause basaloid keratinocytes to proliferate within the epidermis, lifting the lesion above the skin surface. Keratin trapped in the lesion forms horn cysts and plugs that give a waxy, 'stuck-on' look. Lesions do not become malignant. The sudden eruption of many lesions (Leser-Trélat sign) is thought to reflect growth factors released by an internal cancer.

## Classification

- Common seborrheic keratosis (waxy, verrucous, stuck-on)
- Dermatosis papulosa nigra (small dark facial papules in darker skin)
- Stucco keratosis (small grey-white papules on the lower legs and feet)
- Irritated or inflamed seborrheic keratosis

## Symptoms and signs

- Sharply defined, round or oval papules or plaques, tan, brown or black
- Waxy, warty or greasy surface that looks 'stuck on' the skin
- Most often on the [chest](https://durgical.com/en/anatomy/region/chest/), back, face and neck; never on palms or soles
- Usually painless; may itch or bleed when rubbed by clothes
- Number increases slowly over years

## Red flags

- Sudden appearance of many seborrheic keratoses, often with itch: Leser-Trélat sign, look for an internal cancer (mostly gastrointestinal adenocarcinoma, especially gastric)
- A lesion that changes quickly in size, colour or shape, bleeds without trauma or ulcerates: biopsy to exclude melanoma or carcinoma
- A single pigmented lesion that looks different from the patient's other lesions ('ugly duckling')

## Diagnosis

**Clinical**
Clinical diagnosis by its stuck-on, waxy, verrucous appearance in an older adult. Dermoscopy shows milia-like cysts, comedo-like openings, fissures and ridges ('brain-like' pattern) and a sharp border.

**Tests**
Shave or excisional biopsy with histology when the diagnosis is uncertain or melanoma cannot be excluded. With an eruptive presentation (Leser-Trélat), age-appropriate cancer screening, including upper endoscopy and colonoscopy, is guided by symptoms.

**Imaging**
None for the lesion; imaging only as part of a cancer search in the Leser-Trélat sign.

## Differential diagnosis

- Melanoma (the most important to exclude)
- Pigmented basal cell carcinoma
- Melanocytic naevus
- Actinic keratosis and squamous cell carcinoma
- Viral warts and solar lentigo

## Goal of treatment

Confirm that the lesion is benign; remove it only when it is irritated, symptomatic, cosmetically troublesome or diagnostically uncertain.

## Treatment

**Conservative**
No treatment is needed for typical, asymptomatic lesions; explain that they are benign and not contagious.

**Procedure**
Cryotherapy with liquid nitrogen, curettage, shave excision or electrodesiccation; lasers in selected cases. Send tissue for histology when there is doubt.

**Follow-up**
Teach the patient to recognise a lesion that changes or looks different from the rest; whole- [skin](https://durgical.com/en/anatomy/skin/) examination in people with many pigmented lesions.

## Complications

- Irritation, itch, inflammation or bleeding from friction
- Pigment change or scarring after removal, especially in darker skin
- Misdiagnosis: a melanoma mistaken for seborrheic keratosis

## Prognosis

Benign, with no malignant potential. Lesions persist and new ones appear with age; removed lesions rarely recur, but others develop.

## Test yourself

Think of the answer, then tap the question to see it.

## What is the classic description of a seborrheic keratosis?

A waxy, well-defined, tan to black papule or plaque that looks 'stuck on' the skin.

## What is the Leser-Trélat sign?

The sudden eruption of many seborrheic keratoses, a paraneoplastic sign mostly of gastrointestinal (especially gastric) adenocarcinoma.

## Which dermoscopic features suggest seborrheic keratosis?

Milia-like cysts, comedo-like openings and a brain-like pattern of fissures and ridges.

## When should a seborrheic keratosis be biopsied?

When the diagnosis is uncertain, especially if melanoma cannot be excluded (rapid change, bleeding, an 'ugly duckling' lesion).

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## Related conditions

- [Melanoma](https://durgical.com/en/conditions/melanoma/)
- [Melanocytic nevi and dysplastic nevus](https://durgical.com/en/conditions/melanocytic-nevi-and-dysplastic-nevus/)
- [Actinic keratosis](https://durgical.com/en/conditions/actinic-keratosis/)
- [Basal cell carcinoma](https://durgical.com/en/conditions/basal-cell-carcinoma/)
- [Cutaneous squamous cell carcinoma](https://durgical.com/en/conditions/cutaneous-squamous-cell-carcinoma/)
- [Viral warts (verruca)](https://durgical.com/en/conditions/viral-warts/)
- [Gastric cancer](https://durgical.com/en/conditions/gastric-cancer/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Seborrheic keratoses: Overview](https://www.aad.org/public/diseases/a-z/seborrheic-keratoses-overview) (American Academy of Dermatology, 2026).

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/seborrheic-keratosis/