Nail fungus, also known as Onychomycosis, is most often caused by small microscopic organisms related to mold and mildew. It can sometimes be caused by yeast as well, but this is more rare.

These fungus organism develop in the toe nails most often, but fungus can develop in finger nails as well. The fungus thrives on dark, moist, warm environments, and they get these most often on the feet because people wear tight fitting shoes most of the day. When the shoes are tight, or you're wearing socks or other foot covering that does not allow your foot to get air, it can sweat. This provides the moisture along with the darkness inside your shoe that the fungus loves.

In most cases, nail fungus is caused by poor foot care or small abrasions, cuts or damage to the feet that allows the fungus to get under your nails. Nail fungus is also contagious though, so you can pick it up just by using public showers at the gym, going to a public swimming pool, or sharing towels with someone else who has a nail fungus infection.

There are many other common reasons people have nail infections. Technically these aren't a cause of nail fungus by themselves, but they help to make the conditions for nail fungus ripe.

If you're not taking care of yourself well and your body's immune system is low, you're at more of a risk for getting nail fungus than when you're immune system is strong. People with diabetes for instance, are more susceptible to nail fungus infections because their immune systems are compromised. Someone with HIV has the same additional risks.

If you don't take care of your feet and toe nails well, this could also be a cause for nail fungus. Getting ingrown toe nails for instance, and not taking care of them right away, can cause debris to be built up around the ingrown toe nail area. Depending on the severity of the ingrown toe nail, it can also pierce or wound the skin, which gives the fungus a place to take root.

Wearing very tight shoes, and socks or hosiery which makes your feet sweat can also cause nail fungus infections. Shoes that are too tight will rub the big and little toes of your feet, causing small injuries which allow fungus to get under the nails. Letting your feet sweat all day can also be a cause of nail fungus, because the fungus thrives on the moisture.

Simple ways to help prevent nail fungus are the opposite of some of the things that cause nail fungus. Wear cotton socks so your feet can breath throughout the day. This will keep them drier so the fungus is robbed of the moisture it needs. Wear shoes that fit properly too. When possible, go without shoes so your feet can breath even more. Get out in a sun a bit without shoes or socks too, the UV rays from sunlight will help keep your feet dry, and provide plenty of light - both of which are impossible for fungus to breed or live in.