How Can Hyperpigmentation In The Underarms, Groin Area And Knees Be Treated?

Hi, I am 18 years old slim girl. My underarms, groin area, inner thighs, knees are very dark compared to rest of my body. Initially I thought it is normal and common to have dark underarms and groin area. But then realisation hit me hard. It s not the same for everyone. I noticed my friends wearing cut sleeves and flaunting their flawless underarms. It made me feel insecure. A lot. I have tried scrubbing, home made packs, and nothing seems to work. I really really feel so underconfident. I am pretty looking, slim girl and these dark areas are taking a toll on my self esteem. I feel so insecure and conscious about it. I have stopped wearing anything that reveals my dark, ugly areas. It feels bad. Very bad. I did a lot of research and thought that I could be having Acanthosis nigricans. But I am not over weight at all. I read that it s difficult getting rid of the dark patches. It s disturbing me a lot. I want these to go. I ve never in my life felt so insecure about myself. Please help me.