Ingrown toenails are a common, painful condition that occurs when skin on the side of a nail grows over the edges of the nail, or when the nail itself grows into the skin.
Ingrown toenails can develop for many reasons. In some cases the condition is congenital, such as toenails that are simply too large or there is too much tissue at the side of the nail, this is called ungulalbia. This excessive ungulabia can have a tendency to "roll up", and around the nail border that allows the nails to puncture the tissue.

Pain and commonly infection will then follow.