My nail keeps spliiting, how to fix?!?

one of my nails keeps splitting down the middle as it grows out. i don't think this can be fixed with a polish or sealer because there is a white line down the middle of my nail underneath it. as it grows out i notice the skin is different in the middle of my nail then the rest of my finger. i had gotten this once i had a receptionist job for over a year...is it from constantly typing?? is there any way i can fix this problem?