Nail fungus is a common disorder that leads to yellow or chalky white, brittle, cracked, and thick nails. Fungal nail infections, called onchomycosis, most often affect toenails. Nail fungus is more common in men and those with weakened immune systems, including people with diabetes. Most fungal nail infections do not cause complications. If you are uncomfortable with the appearance of your nail fungus, your doctor may recommend an antifungal medication. You may need to take the medicine for several months. Follow the links below to find WebMD's comprehensive coverage about how nail fungus is contracted, what it looks like, how to treat it, and much more.