Although it is rare, some people suffer Koilonychia, in which their toenails grow upward. If not properly attended to, they can lead to discomfort when wearing footwear. Sometimes it is thought to be caused by an iron deficiency, although patients without the deficiency have been known to have it as well. Sometimes it is seen in both parents and children, suggesting that it is a genetic condition. Consistent care is the most important approach, when dealing with upgrown toenails.
Wash your feet in warm water and dry them thoroughly with a towel. Since upward growing toenails tend to rip more often -- and therefore expose themselves to infection -- careful hygiene is important. Use a nail cleaner, to remove any dirt under the nail.
Cut the toenail down to the point where it begins to curve upwards. Do not over cut them, so that they bleed and grow inwards. Instead, aim for an even nail.
File the nails with an emery board, to ensure that they are smooth and will not catch on socks.
Find thick socks that will provide more cushion against the friction between the toenails and the shoe. You may also want to try a natural fiber sock, as they allow the feet to breathe easier and therefore keep the feet more comfortable.
Inspect the toenails at least weekly. Trim them frequently to prevent discomfort.
Consult a doctor first, to ensure the problem can't be corrected with iron supplements.