Given all the events going on around us, this may seem trivial. However, you have to remember that I am over 60, so some of what comes out of my mouth has to do with health and ailments. That being said, here is a posting about fingernails, or really just a thumbnail.
When I was young, I injured my right thumbnail while weightlifting. I don't remember if it eventually fell off, but I know I've had a "bump" and a vertical ridge in the middle of it for years. In my mid-50s, my fingernails started to grow thinner and the thumbnail in question started to split at the end. I had to keep the nail clipped very closely or I would have splitting problems.
My doctor recommended certain vitamin combinations that he said would help, but I already take a large number of vitamins and other supplements. I have for years. I had already been taking those vitamins/supplements, but I did increase the ones he suggested. Before you ask, I don't remember for sure the ones he recommended, but I think they were selenium and chromium picolinate. Anyway, increased doses did not help.
I tried nail hardeners, but finding one for men that is not shiny is nearly impossible. After a lot of searching online, I found a hardener with a fairly satin finish. It made my nails look healthier, but it didn't prevent the splitting. Back to the Google drawing board.
Finally I discovered that some folks recommended Biotin for healthy nails. Biotin is considered one of the B vitamins and is sometimes called Vitamin H. I've read that it makes your hair and skin healthier too, but since I'm mostly bald and have both seborrhea and rosacea, I can't say it helped in those areas, but it really helped my thumbnail.
I started with a small dose of Biotin daily and noticed some improvement over several weeks. Then I found Biotin sold in 5 mg capsules, and I started taking those. Since I have increased my dosage to 5 mg every day, I no longer experience the split thumbnail. The bump and ridge are still there and always will I suppose. According to current medical knowledge, there is no way to repair a damaged nailbed.
End of story. If you stayed with me on this, now's your chance to tell me some of the bad side-effects from taking a high dose of Biotin. I'm waiting, but I hope there aren't any.