Mole vs Seborrheic Keratosis: Telling the Two Apart

A seborrheic keratosis is a benign overgrowth of keratinocytes (the main cells of the epidermis). It's not a mole, not a precancer, and not related to melanoma. The growth pattern is in the upper layer of skin, sitting on top.

Classic features:

Waxy, 'stuck-on' appearance — looks like it could be peeled off (it can't, but appearance suggests it).

Colour ranging from skin-tone to tan, brown, or near-black.

Rough, warty surface texture (can feel like a clump of crumbled wax).

Well-defined borders, often with a 'shoulder' between the lesion and surrounding skin.

Size from a few millimetres to several centimetres.

Location anywhere on the body except palms, soles, and mucosa — most common on face, chest, back, and shoulders.

Usually multiple in middle-aged and older adults.

Gradual development over years; no acute appearance.

SKs do not bleed spontaneously, do not ulcerate (though they can be irritated and bleed if scratched), and don't cause symptoms beyond cosmetic concern. They are entirely benign and never transform into cancer.

True moles (melanocytic nevi) and SKs are different lesions with different cell types. Distinguishing features:

SKs: - Appear later in life (40+) and accumulate with age - 'Stuck-on' waxy appearance, sometimes pearly or matte - Colour can be very dark but often has uniform tone or a 'speckled' pattern of small dark dots within the tan - Surface texture rough, warty, or scaly - Can be picked or scratched off (though this isn't recommended) - Multiple, often clustered

Moles: - Usually present from childhood or early adulthood - Smooth or slightly raised, integrated into the skin - Colour usually uniform brown, may darken with sun exposure - Surface smooth or only slightly rough - Don't peel off; firmly part of the skin - Some scattered, some grouped, but rarely as densely clustered as SKs in older adults

The distinction can be challenging by naked-eye examination, especially for darker SKs. Dermoscopy reveals characteristic SK features (milia-like cysts, comedo-like openings, fingerprint-like patterns) that are absent in moles. Dermatologists can usually distinguish them in seconds with dermoscopy.

Several SK features mimic melanoma:

Dark colour. Some SKs are very dark — almost black — and look like pigmented lesions of concern.

Irregular borders. SK borders can be jagged or 'geographic.'

Multiple colours within one lesion. Some SKs have varying shades from tan to black within a single growth.

Asymmetric shape. Many SKs are asymmetric.

Larger than 6mm. Many SKs are several centimetres.

Apply ABCDE to a typical pigmented SK and several criteria might 'flag' it as concerning. The result: SKs are one of the most commonly biopsied lesions in dermatology, even though most are obvious to experienced eyes.

The distinguishing features that point toward SK rather than melanoma:

'Stuck-on' waxy appearance — this is highly characteristic of SK.

Multiple similar lesions in middle-aged or older patient.

Gradual development over years rather than recent appearance.

Classic dermoscopic features visible to a dermatologist.

No bleeding without trauma, no ulceration, no symptoms.

When in doubt, dermatology evaluation is the right step. A dermatologist's dermoscopic examination resolves most SK vs melanoma questions in a single visit.

Most SKs need no treatment beyond reassurance. Reasons to seek evaluation:

Uncertainty whether a lesion is SK or melanoma. Dermatology dermoscopy clarifies.

Cosmetic concern about location (face, scalp, hands).

Irritation from clothing, jewelry, or grooming activities.

Sudden appearance of multiple SKs (the Leser-Trélat sign — rare association with internal malignancy that warrants medical evaluation, though most cases are coincidental).

A 'SK' that has changed in a way that doesn't fit normal SK behaviour — bleeding without trauma, rapid growth, ulceration. This raises possibility that it's not actually a SK.

For cosmetic removal:

Cryotherapy (liquid nitrogen freezing). Quick, 1-2 minute treatment. Lesion turns dark, may blister, then peels off over 1-2 weeks. May leave a slightly lighter spot.

Electrodessication. Small electrical current burns off the lesion. Local anaesthetic for larger lesions.

Curettage. Scraping off with a curette under local anaesthetic.

Shave excision with pathology. Used when there's any clinical doubt about the diagnosis.

Most cosmetic SK removals are not covered by insurance because they're not medically necessary. Multiple-lesion treatment sessions can be cost-effective if you have many to address.

The Leser-Trélat sign is the sudden eruption of multiple seborrheic keratoses, sometimes with itching, sometimes associated with an underlying internal malignancy (most commonly gastrointestinal or hematologic cancer).

Classic presentation:

Multiple new SKs appearing in a relatively short period (months) on someone who didn't previously have many.

Often associated with itching of the new lesions.

Often in adults over 50.

The association with cancer is debated in dermatology literature. Some cases clearly involve underlying malignancy; many cases turn out to be just an unusual pattern of normal age-related SK development.

If you experience sudden eruption of multiple SKs over weeks to months, especially with itching, see a dermatologist for evaluation and consideration of internal evaluation. Most cases are benign. The minority that involve underlying malignancy benefit from earlier diagnosis.

Within 4-8 weeks if any:

Uncertainty whether a lesion is SK, mole, or melanoma.

Multiple new SKs appearing over months (rule out Leser-Trélat).

Cosmetic concern about specific SKs.

Irritation from clothing, jewelry, or grooming on a SK.

Within 2-4 weeks if any:

A 'SK' that bleeds without trauma.

A 'SK' that has rapidly grown or changed.

A 'SK' that doesn't fit normal SK behaviour — your dermatologist will assess whether it's actually a SK.

For most SKs, no appointment is needed. Reassurance about benign nature is the right management. Annual full-body skin check during routine dermatology visits will identify SKs and confirm they're benign.

The overall posture: SKs are extremely common, almost always benign, and confused with melanoma only because of imperfect feature recognition. Dermatology evaluation resolves uncertainty quickly.