Seborrheic Keratosis

Seborrheic keratosis (SK) is the single most common benign skin tumor, affecting nearly all adults over 60. They appear as waxy, raised, brown or tan growths that look as though they have been pasted or stuck onto the skin surface.

The stuck-on appearance is the hallmark feature. SKs have a well-defined border, a waxy or greasy surface texture, and often show a crumbly, rough surface when examined closely. They can range from a few millimeters to several centimeters and vary in color from light tan to dark brown or even black.

SKs are a leading cause of unnecessary dermatologist referrals because dark-colored variants can closely mimic melanoma. The key differences: SKs have a stuck-on, waxy appearance and can often be felt to sit on top of the skin, while melanoma tends to be flatter and more integrated with the surrounding skin. SKs have a uniform waxy texture throughout, while melanoma shows color variation.

SKs are completely benign and require no treatment. They do not progress to cancer. However, they are sometimes removed for cosmetic reasons, if they are irritated by clothing, or if there is diagnostic uncertainty. Methods include cryotherapy, curettage, and electrodesiccation.

The sudden appearance of numerous SKs (the sign of Leser-Trelat) has historically been associated with internal malignancy, though the clinical significance of this association is debated.