Why have fine lines started appearing recently under just one eye?

I've noticed recently that under my right eye there are fine lines , i thought they were smile lines but when i'm not smiling they're still there.They're are faint, i don't understand how they just appeared under one eye? On my left eye i don't get smile lines. I'm nearly 17, i'm not sure what has caused it, should i try a cream that contains retanoid? I noticed one line when about 6-8 months ago,now its multiplied to 4 small lines near the side under my eye! , do you know what's caused it?

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