"Bruise" on Areola?

I'm 16 years old. And I didn't know who to ask about this. But I woke up this morning with this bruise looking spot on my left breast. And I'm not sure how it got there. It isn't painful. As far as I know, there isn't any lumps in my breast. And my family hasn't had a history in really any health conditions. But I'm still concerned. Does anyone know what this could be?