An ingrown fingernail or toenail: An acronyx is a common form of a toenail ailment which is often painful because, while growing, it cuts into one or both sides of the "nail bed".

While acronyxes, or ingrown nails, can occur in the nails of the hands and feet, they usually exist most commonly with the toenails.

A more accurate description of an acronyx is that there is too much skin around the nail ("overgrown toeskin"), and so the nail itself is seldom the problem.

The most common place for acronyxes is in the big toe, however ingrowth can actually occur on any nail.