Seborrheic keratoses are raised growths on the skin. Seborrheic means greasy and keratosis means thickening of the skin. There may be just one or clusters of dozens. They are usually start off light tan, and then may darken to dark brown or nearly black. They may be oval spots a fraction of an inch across, or form long Christmas tree like patterns on the torso inches long.
The consistent feature of seborrheic keratoses is their waxy, pasted-on or stuck-on look. The look is often compared to brown candle wax that was dropped onto the skin. They may be unsightly, especially if they begin to appear on the face.
These are not contagious and do not spread. They have no relationship to skin cancer and do not pose a risk to health. They get darker after sunless tanning creams have been used. Unlike moles (Nevi), they never turn into melanoma. As people age they may simply develop more, and some people grow more than others. Sometimes seborrheic keratoses may erupt during pregnancy, following hormone replacement therapy or as a result of other medical problems.
They are mostly hereditary and not caused by sun exposure. One often inherit the pattern and favored locations they grow on. They often are found on the trunk and where the face meets the scalp. A different type of seborrheic keratosis may grow in liver or age spots (solar lentigines), but there are usually only a few of these. Some rough, brown keratoses on the face are actually actinic keratosis from sun damage.
Clothing rubbing against can get them irritated and make them grow. Alpha-hydroxy lotions and mild topical steroid creams may help this. If they get very itchy, irritated and bleed easily they should be removed. When a seborrheic keratosis turns black it may be difficult to distinguish from a skin cancer without a biopsy.
Because the keratoses are superficial, their removal shouldn't result in much scarring. Local anesthetics can be used to make the treatment painless. There may be a little discomfort as the treated area heals. Most often liquid nitrogen (cryosurgery) is sprayed on the spots, and produces blisters that lift up the seborrheic keratosis. These form into scab-like crusts that fall off within a few weeks. Occasionally there may be a small dark or light spot or a scar. These will fade over time. Sometimes part of the growth will eventually return.
Another treatment often done is scraping off with a curette (ED&C). This is more useful when only a few need to be done, and one really wants them not to come back. It is also used when one spot needs a biopsy, since the scrapings can be sent to a lab. Healing is slower and scarring is more common. Sometimes seborrheic keratoses are burnt off with an electric needle or laser, especially if they are small.
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