Darkened inner eye corner. Any suggestions? (photos)

Hello doctor I am 21year old female. My inner eye waterline is dark. I have this condition since the last year ( i have noticed it then). One of my friend said "wipe that discharge from your eye". But it is not the eye discharge. Im self conscious about this. No matter how many times I wash it with soap and water it wont go. I have this condition for both of my eyes. I want to know what may be the cause for it and a cure for this. Thanks for answering in advance.

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