For most of my life, I had terrible nails. As a child, I was a nail biter but finally outgrew that only to start using artificial nails. After several years of that expense, I finally walked away. Unfortunately, I walked away with paper-thin nails that tore if you looked at them wrong. I have tried numerous nail strengtheners and products, but have finally gotten the nice natural pretty nails that I always wanted!
There are multiple nail strengthener types but the primary are polish style and oil treatments. I have found that while the polish types do keep my nails hard, they still are not strong from the inside out.
The primary issue that I had most recently was the fact that my nails peeled in layers, like split ends on the hair. The polish types (Nailtiques, OPI Nail Envy, and such) did help prevent that peeling, however, my nails actually became almost too hard. Those treatments were great right after the fake nails came off, but as my own nails grew back healthier, the hardeners made them more prone to actually breaking. That was not the help I had in mind!
Now I tend to buff them weekly to keep them smooth, and I use Pampered Skin Care Ultra Protein Rich Nail Serum frequently. I also use other oils and creams to keep them nourished yet flexible which seems to be the magic combination. I did stop using emery boards and nail clippers altogether, and use only a glass file to trim and shape them.
After years of fighting to have any nail at all, I now find myself having to trim them back every other week or so. So healthy nails win over brittle or peeling!