Dryness, nutritional deficiencies, fungal infections, trauma to the toenail and exposure to chemicals can cause a splitting toenail, according to Sierra Foot & Ankle. Thyroid disease and psoriasis are other possible causes of a splitting toenail, notes Everyday Health.
Exposing the nail to water repeatedly is a common cause of nail dryness, states Sierra Foot & Ankle. The nail expands in response to moisture and contracts when it dries, a cycle that compromises the structure of the nail and leads to cracking.
Fungal infections, responsible for half of toenail disorders, cause toenails to discolor, thicken, become misshapen and split, explains eMedicineHealth. These infections are more common in older people.
Wearing shoes that do not fit well can put pressure on toenails, states Sierra Foot & Ankle. The repetitive stress on the toenails that results can cause pain and splitting of the toenails.