1. If the upturned nail is thin, it is lack of trace elements, such as selenium, iron, zinc, calcium, etc. If you are not picky about food, you can correct it with comprehensive nutrition and supplement trace elements.

2. If the upturned part of the nail is thick, yellow or lime-like white or gray-black, it is generally a fungal infection (mainly mold), also known as onychomycosis. It's about to be treated. The side effects of oral drugs against fungal infection are relatively large, and children are not suitable for eating, so they can be treated with external drugs.