Ingrown toenails (onychocryptosis) are common nail complaints and may occur at any age. They result from the penetration of the nail plate into the skin. There are 2 types of ingrown toenails: lateral and distal.

Lateral ingrown toenails are the most common type, especially in children and young adults. The nail becomes embedded into one or both lateral nail folds, with a nail spicule that breaks the epidermis of the lateral groove with subsequent inflammatory reaction and pain. Cutting the spicule aggravates the condition by causing a new, more proximal spicule to form. In time, granulation tissue may develop with concomitant oozing, bleeding, and secondary infection. The condition may be precipitated by improper nail cutting, plantar hyperhidrosis, trauma, and anatomical foot abnormalities.

The second, and much less common, type of ingrown toenail occurs distally. Normally, there is a natural counter pressure from the nail plate to the underlying tissue. Nail plate avulsion or traumatic nail shedding cause a loss of counter pressure, causing a bulbous extremity. The newly formed nail abuts this distal wall, which interferes with its normal growth. A deep transversal horn fills the distal groove and results in the ingrown nail and pain.