Several years ago, I noticed pitting in in my fingernails. Each nail has minor pin like dents. They usually for in horizontal rows across each nail - seemingly at the same time. And, they continue to grow out to the end. Normally, a new row starts again before the previous ones are gone/grown out. Any ideas as to the cause of this? I noticed it at least 5 years ago, but it has likely been occurring for much longer.