Nail fungus is caused by a fungal spore infection of the toenails. Fungus is most common in a dark, warm, moist environment, which is why it’s a common condition for people to experience on their toenails. The fungi feed on the nail’s protein, keratin.
Some infections are small and easily contained, while with other patients it can spread quickly. When the fungal infection moves away from the toenail onto the skin on or between the toes, it is known as athlete’s foot. Often, these two conditions go hand-in-hand as both these infections spread easily.