what are the two grey lines on both my middle finger nails?

[Yusha4840]

hi I'm am a 15 year old Pakistani male and I have 2 thin greyish lines on both my middle fingers of both my hands. I don't know if this a coincidence that they are on both of my middle fingers. the line on the left hand is slightly thinner and looks slightly different to the one on my right hand. The line on my left hand is slightly thicker and visible through the cuticle.  I have no lines on my toenails.I developed these lines from the age of 12 or 13 and they haven't changed in appearance, colour and size since then. Nobody in my family has these lines on their fingernails. I just wanted to know if these are a benign cause of melanonychia straita or something more serious. will these go away in the future or will I go to see a dermatologist. It would be really helpful if somebody can give an explanation of why I developed these lines on both of my middle finger nails even though nobody in my family has them. if you want I can attach pictures. I really hope for a response. Thanks