I have this problem, too, and also
on my
fingernails, and it is a condition called psoriatic nails, and people with psoriasis have this problem. This skin problem is in our family, although I have no major issue with skin manifestation, my brother is covered from head to toe with plaques and suffers. I have mild form. But interestingly, psoriasis is an outward skin manifestation of other systemic disease, including high iron.
Take care...