Thick toenails are most commonly caused by a fungal infection known as onychomycosis. [8] X Expert Source Miguel Cunha, DPMBoard Certified Podiatrist Expert Interview. 22 April 2020. Thickening of the nail can also be caused by repeated injury to the toenail. This is often seen in athletes, but it can also be the result of wearing improperly-fitting shoes. Other causes of thick toenails include aging and underlying conditions like psoriasis and diabetes. [9] X Research source
Treating severe cases of fungal infection may require the removal of the nail in order to fully treat the nail bed below.
Thick toenails can also be caused by wearing shoes that are too tight. Wear shoes that fit properly, especially when engaging in strenuous activities.
