11 Endocrine Disorder Symptoms You Should Not Ignore

8. Darkened skin patches or sudden skin thickening (acanthosis nigricans)

Thickened, darkened skin patches—often on the back of the neck, under the arms, or in skin folds—are commonly associated with insulin resistance. This sign, called acanthosis nigricans, is more visible in darker skin tones and can be one of the earliest outward clues that blood sugar regulation is off. People may attribute the change to poor hygiene or friction from clothing, but when these patches appear or worsen alongside weight gain, excessive thirst, or fatigue, it’s worth checking blood glucose and insulin-related risk factors. Lifestyle changes—improving diet, increasing activity, and losing modest weight—often help, and a medical evaluation can determine whether medications are needed to prevent progression to type 2 diabetes. Because this sign is visible, it’s a helpful prompt to begin earlier conversations with your doctor about metabolic health and family risk.