###Human: Why are my arms, neck and underarms blackish when compared to the rest of my body? ###Assistant: Hello. I understand that you are concerned. Looking at your photographs, I can appreciate that you have two things (attachment removed to protect patient identity). 1. Acanthosis nigricans: The darkening of the neck and underarms is due to thickening of the skin, known as acanthosis nigricans. It is a manifestation of insulin resistance and is usually associated with diabetes mellitus, weight gain, obesity, thyroid disorders and certain drugs. Sometimes no cause can be identified. 2. The arms darkness seems simple tanning due to sunexposure as I can appreciate the sharp cut off at the arm, where sunexposure ends the skin is fairer. Use the following medications: 1. Kojic acid cream apply once at night for pigmentation. 2. Suncros sunscreen lotion apply three times every three hourly on sun exposed areas during day time. 3. Tablet Limcee (Vitamin C) one tablet once a day after breakfast. Get following investigations done 1. FBS. 2. T3,T4, TSH. 3. Fasting lipid profile. Please review with reports.