I have this kind of white powder under the toenails of one foot. The nails are lifting and it hurts around the foot.

It is possible that the user has a fungal infection under their toenail, also known as onychomycosis. They should consider using over-the-counter products like CANESTEN, EMTRIX, or FUNGICURE to treat the infection. It is important to follow the recommended application instructions and take preventive measures to slow down the infection, such as avoiding sharing nail clippers, keeping nails trimmed, and wearing sandals in public showers. Regularly changing socks and practicing good foot hygiene can also help. If the infection persists or worsens, it is advisable to consult a healthcare professional for further treatment options.