Thanks to xoxolove! Is it true that friction of the jeans to our knees make it dark? Because most of the I wear jeans, because you know I don't have the confidence because of dark knees. And what's the best way to apply lemon? I found lots of procedure in the net and I could not choose the best one.
And one thing more do you have any suggestion on how can I get rid from my dandruff?

I don't think your knees get dark from jeans. Usually people with dark skin or medium tone skin get dark knees and elbows.

You should squeeze the juice from a lemon and mix it with an oil or moisturizer. I put lemon juice in rosewater and apply it. Then I use any lotion on my skin.