A dark ring around the neck can be a symptom of insulin resistance, warns the National Institute of Health. Known as acanthosis nigricans, the dark patches of skin can also appear on the back of the neck, armpits, elbows, knees and knuckles.
Acanthosis nigricans appears most often in people who are obese or have type 2 diabetes, says Mayo Clinic. It afflicts Native Americans, Hispanics and African-Americans most. The skin becomes thicker and velvety in texture, and may produce a strong odor. Some patients have reported that the area itches. The changes are very gradual, developing over the course of months or years. Rarely, acanthosis nigricans is a symptom of cancer. The darkened skin folds indicate a cancerous tumor growing in an organ, usually the stomach, liver or colon. Acanthosis nigricans can also be hereditary.
While insulin resistance has few symptoms, when the condition becomes severe people are more likely to develop acanthosis nigricans, warns the National Institute of Health. It is known as one of the physical risk factors that the American Diabetes Association recommends testing for.
To treat acanthosis nigricans, Mayo Clinic recommends losing weight, taking medications, removing any cancerous tumors, and using a topical antibiotic or soap to remove odor. Laser therapy may also help reduce the skin's thickness, improving the appearance.