Neck, armpits and groin
Dark, velvety patches found in your armpits and on your neck and groin are likely acanthosis nigricans. This slow-developing skin condition, which is more common in overweight and obese adults, can be a sign of type 2 diabetes. Researchers believe that insulin resistance (which causes high blood sugar and can lead to type 2 diabetes) can send some skin cells into overdrive, increasing skin thickness and darkening pigment.
Protect Yourself: To help prevent diabetes, pay particular attention to your diet. Filling up on high-fiber foods (think oatmeal, beans, and broccoli) can slow the body's absorption of sugar and, as a result, may keep blood sugar within a healthy range. One study found that prediabetics who consumed the most fiber were 62 percent less likely to develop full-blown diabetes than those who consumed the least.