I had horizontal ridges on my thumbnails and did not know why. Thought it was possibly a fungus. I went to the dermatologist, who told me, "Stop touching your thumbs. Let the manicurist take off the cuticle, not you." I said, "I don't!" He asked me if I get dry calves, elbows, and hands, and I said, "Not particularly," but then I did notice that those areas of my skin were a bit dry. As I left the office, I impulsively curled in my pointer fingers to rub off my thumbnail cuticle. That is when I realized that I WAS in fact rubbing out my own cuticle and messing with the nails. I vowed to catch myself in this impulse and not touch them, and turns out in a few months the thumbnails grew in smooth and normal.