In general, if the thumb nail protrudes is the result of the following factors: 1. The nail is susceptible to infection by bacteria, viruses, fungi and other undesirable factors, especially in the case of fungal infections, the condition of gray nail will appear. If the thumb nail protrudes, consider whether there is a middle nail that turns gray and becomes brittle and easy to fall off. In this case, it is usually considered as gray nail disease, which is caused by fungal infection.2. When the body is deficient in vitamins, such as vitamin B and vitamin A, the nail cap will also become convex, and the nail will be brittle and easily folded at this time.3. In some cases of peripheral neuritis, especially when diabetes is combined with peripheral nerve radiculitis at the fingertips, the nail will In some cases of peripheral neuritis, especially diabetes combined with peripheral radiculitis of the fingertips, the nails will protrude and be accompanied by pain and itching of the nails and fingertips.