Telling the difference between precancerous skin lesions and normal age spots

Q. How do precancerous skin lesions differ from normal age spots?

A. Not all marks or growths that develop on skin are worrisome, though they may look alarming. Dr. Joseph Merola, a dermatologist at Brigham and Women’s Hospital, says that skin lesions that can develop into cancers look different from the normal changes with age. The most common precancerous skin lesion is actinic keratosis, a red scaly bump or patch of skin that may form a scab and fall off, but never seems to heal. It usually appears in areas of the body with high sun exposure.

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A small percentage of these lesions develop into a cancer called squamous cell carcinoma. Merola says that lesions on certain body parts — such as the earlobes and lips — are more likely to spread if they become cancerous. On the lips, the condition is called actinic cheilitis, and usually involves a chronically cracked, chapped, and inflamed lip. Actinic keratosis is often treated by killing off the affected cells with liquid nitrogen or a topical cream.

Large or abnormal moles can turn into melanoma, though most do not. Changes in moles are a warning sign to see a doctor.

Patients often worry about growths or discolorations of age, Merola says. A common one is seborrheic keratosis — benign, wart-like growths with the appearance of brownish candle wax. “They’re like the barnacles of aging,” Merola says. “They’re not cosmetically appealing but they cause no harm.” A lentigo, an irregular brownish spot on the skin sometimes called a liver spot, also usually poses no concern, though doctors may monitor it for any changes.