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Seborrheic Keratosis
A seborrheic keratosis is a very common, completely benign skin growth that tends to appear with age. It looks tan to dark, sits slightly raised on the skin with a waxy, rough surface, and has a typical “stuck-on” appearance.
What Happens in the Skin
A seborrheic keratosis is a benign overgrowth of keratinocytes, the cells of the skin’s surface layer. These cells pile up and thicken in one spot while staying fully contained within the epidermis. That containment is the key contrast with cancer, which grows down into deeper layers of the skin.
What causes seborrheic keratosis?
Seborrheic keratoses form when surface skin cells multiply and accumulate outward, rather than spreading into the skin. They are not viral and not contagious. Several factors influence who develops them and how many appear, though the growths themselves stay harmless throughout.
Age and Cell Accumulation
Age is the main factor. Over time, keratinocytes can proliferate and build up in localized areas, forming raised, waxy growths. They are sometimes informally called “age spots” or “wisdom warts,” but they are neither true warts nor a sign of anything dangerous developing in the skin.
A Genetic Predisposition
Seborrheic keratoses often run in families and appear in multiple spots across the body. This genetic predisposition helps explain why some people develop just one or two while others accumulate many over the years, often in similar locations to those seen in close relatives.
The Outward, “Stuck-On” Growth Pattern
These growths develop outward, sitting on the surface with neat, well-defined borders, which gives them their characteristic pasted-on look. This pattern differs from melanoma, which tends to grow into the skin with irregular, blurred edges. The contrast is “resting on” versus “growing into” the skin.
A Role for Sun Exposure
Cumulative sun exposure can contribute to where seborrheic keratoses appear, as they are often found on areas that have seen years of sunlight. Even so, they remain benign growths and behave very differently from sun-related lesions that require medical attention.
