So I noticed just the other day that my twin girl has this vertical indentations going across some…

So I noticed just the other day that my twin girl has this vertical indentations going across some of here nails. It's kinda hard to see but it's only on about 4 nails and not her thumbs. I tried looking up what it could be but only find a couple things about it. Was just thinking it was a vitamin deficiency. They drink formula, I would think that has everything in it they need