Why are my thumb nails growing split in the middle, from the quick?

I have very healthy strong nails. I keep them filed, clear or no polish, but they would grow long very quickly if I wanted to wear them long.


(very healthy lifestyle, no drinking or drugs)


In the last month or so they have been growing with this ridge, break, crack right up the middle of both my thumb nails.. all my other nails are fine.


It's not cracked all the way to the top of my nail, yet, after my nails keep growing for another month or so it will reach the top.


Any idea why this just started happening and how I can get them to start growing normal, unsplit, again.


TIA!!Why are my thumb nails growing split in the middle, from the quick?
Strangely, such splits are usually indicative of damage to the nail bed.