Seborrheic keratosis

Also called SK, seborrheic wart

The benign barnacle of ageing skin: waxy, warty, sharply demarcated 'stuck-on' plaques with keratin-plugged surfaces, usually many, usually on the trunk. Their job in your education is to be told apart from melanoma.

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How it looks

Multiple sharply demarcated, waxy, verrucous brown plaques with a stuck-on appearance and keratin-filled surface pits scattered over the back.

Plaque Papule Hyperpigmentation Discrete Truncal

Rose is the lesion, grey the pattern the lesions make, green where on the body it lives.

Across skin tones

Dermatosis papulosa nigra, multiple small dark facial SK-like papules, is a common, benign, often familial variant in deeply pigmented skin.

Symptoms & course

Asymptomatic; may catch on clothing and inflame

Diagnostic approach

Dermoscopy: milia-like cysts and comedo-like openings
Biopsy only when melanoma cannot be excluded

Differential, and how to separate them

Melanoma
Favours it: Flat-ish, colour chaos, evolution, the ugly duckling
Against it: SKs are waxy, stuck-on, keratin-pitted, and come in crowds

Management principles

Reassurance; removal only for irritation or cosmesis

Clinical pearl: A lesion that looks like you could flick it off with a fingernail is usually an SK, but the one that stands out from the crowd still earns dermoscopy.

Keep going

Try the case: Stuck on, not grown in Compare with Melanoma Back to the Atlas