My neck is dark in colour .and after searching on web and seeing pictures etc, I found its Acanthosis Nigerians .my age is 19+ years and height is 6'9" and my weight is 63 kilograms. Which is normal for a boy of my age. I am slim .according to google searches the main reason of Acanthosis Nigerians is fat body .am not fat so where is the problem. Plzz suggest me any lotion or medicine which is easily available which I can buy.