Picture of Congenital Nevi
Congenital nevi are moles that are present at birth. These birthmarks have a slightly increased risk of becoming skin cancer depending on their size. Larger congenital nevi have a greater risk of developing skin cancer than do smaller congenital nevi. All congenital nevi should be examined by a health care provider and any change in the birthmark should be reported.
If a dermatologist believes a mole needs to be evaluated further or removed entirely, he or she will either remove the entire mole, or first take just a small tissue sample of the mole to examine thin sections of the tissue under a microscope (a biopsy). This is a simple procedure. (If the dermatologist thinks the mole might be cancerous, cutting through the mole will not cause the cancer to spread.)
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Text: "Skin Conditions: Pigmented Birthmarks", WebMD Medical Reference, "Skin Conditions: Moles, Freckles and Skin Tags", WebMD Medical Reference provided in collaboration with the Cleveland Clinic