Toenails become yellow, thicker, and hollow inside because the person sweats more, or is in a humid environment for a long time, or works in a humid environment, the nails are immersed in humid water for a long time, which is conducive to the reproduction of a fungus in the nails, this fungus specializes in using the nails as a place to host, a large amount of intake of nutrients in the nails, true or false in the nails after long-term residence, will cause damage to the nails, the nails will Gradually become yellow, even due to the middle of a large number of nails swallowed by the fungus, will cause the hollow, inner hollow nails. So once we often find that the nails become yellow, thick, and hollow inside, we should consider the cause of fungal infection, which may be due to long-term work in the humidity or a lot of sweat from the feet, or other similar reasons.