Toenails will often become thick as an individual grows older. Thickening may also occur as a result of trauma to the toenail, such as when it repeatedly hits the end of a shoe that is too short. Sometimes when something is dropped on the toenail, the nail will fall off. When a new toenail grows back it will often be thicker than it was previously.

Thick toenails can also be seen in individuals with nail fungus (onychomycosis), psoriasis, and hypothyroidism. Those who have problems with the thickness of their toenails should consult a foot and ankle surgeon for proper diagnosis and treatment.