I have a black line down my right thumb, and under neath the end of the white of my nail there is a piece of skin attached to the black line, when I cut my nail it comes off with the nail I've cut but grows back again.
Please contact your GP for them to look at your nail. They may ask you to send a photo by email & they can then decide if it's OK or the photo needs checking by a dermatologist or you need to be referred to a dermatologist. Most nail problems are easily treatable (trauma or fungal infection) but a persistent black line that's not disappearing needs checking out.
