I have a strange not straight lines in my nails.they are black and usualy start in the midle of the nail.not all the fingers have it at same time.?

Trauma?: Black lines run the full length of the nail. Multiple lines are normal and are seen more commonly in african americans. An isolated black line is a nevis or. Ole which may represent a melanoma. An isolated black line needs to be biopsied.

Unsure: Black stipes down one nail could be a subungual hematoma. Red or brown streaks could be splinter hemorrhages. Brown/black lines from the nail plate to tip are often seen in people with dark skin & are normal. Subungual Melanoma can cause nail ridges and dark colors of the cuticle. It usually begin in the nail matrix. It most often effects the thumbs or big toes. Get checked out when in doubt.