I have used fairness cream only on my face; how did my whole body become less dusky?

I have been using Fair & Lovely for past 10 years.I was a dusky teenager. My mother is dusky and my father is very dark. I have my mother's complexion. I also have hypothyroid from the age of 5. I also use lot of natural ways to get a clear complexion like I apply milk to my face, eat a lot of vitamin C. I want to ask that: Can a dusky kid grow up to be fairer naturally? Can fairness cream make my whole body fairer? Or is it related to thyroid? I have stopped using the cream. I am 24+

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