Help! Horizontal ridges on my toenails?

I'm seventeen years old and I just now realised I have faint (but I'm able to feel them) horizontal ridges on my toenails. There are a few nails that don't have any ridges but most of them do. My fingernails have no ridges at all. I looked it up and apparently it can be caused by something serious? Does anyone know what it might be? I have been extremely stressed over the past two or three months could that be a cause?