The most common causes of toenail fungus is the growth of yeast or mold, as stated by the Mayo Clinic. The fungus grows in warm, moist places, such as between the toes.
Some people are more prone to toenail fungus infections than others. Some common reasons the body produces an overabundance of mold or yeast is due to certain medications, such as antibiotics, or a weakened immune system, notes WebMD. Toenail fungus infections are fairly simple to treat through the use of antifungal oral medications. Medicated nail polish is also available. If a fungal infection is severe, a person should contact their doctor.