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Dark skin patches

A ring of dark skin at the back of the neck may look like it's crying out for a good scrubbing. But in reality, it may be acanthosis nigricans, a condition in which the skin appears darker and thicker—even velvety—along body creases.

People with insulin resistance, diabetes, obesity or, in rare cases, cancer, can develop these dark patches. Although not a definitive sign of diabetes, “It makes you think twice and do more workup,” says Heather Jones, a nurse practitioner at Oregon Health & Science University, in Portland, and a member of the Dermatology Nurses Association board of directors.

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