What Causes Fungus on Your Feet?

There are at least four types of fungus responsible for the infection known as athlete's foot, but the most common is the organism, trichophyton rubrum. These infections thrive in warm, moist areas and feed on dead skin, hair and nails. Sufferers often catch the fungus in public areas where people do not wear shoes, such as gym showers. Sharing shoes can also transmit the fungal infection, warns WebMD.

The most-common type of athlete's foot affects the skin between the toes and begins in the area between the two smallest toes. Without treatment, it can spread to the soles of the foot. Moccasin-type athlete's foot begins on the soles of the feet and causes them to thicken and crack. As the infection grows, it may also involve the sides of the foot according to WebMD.

Vesicular athlete's foot causes small blisters to erupt under the skin. This least-common type of infection may affect the bottom or top of the foot, or the area between the toes, reports WebMD.

It is often more difficult to treat a foot fungus involving the toenails, according to Cleveland Clinic. As of 2015, the most-effective treatment for this type of fungus is an oral prescription medication. For an infection that only involves the skin, over-the-counter creams are more-effective than powders.