Nail fungus infection usually starts with the toes. At first you might just notice some puzzling yellow discoloration of a toenail. What you won't see is the network of fine fungal mycelia (like branching stalks) that are spreading out in the sheltered tissue under the toenail.

The fungal growth tends not to spread into the tissue of the toe, at least not right away. Your body's immune system is holding it at bay. Rather, it grows through the matrix of the toenail, getting nutrients from keratin, a protein found in toe- and fingernails. Nails are not living tissue, and they don't produce an immune response to the invader, so a nail fungus infection can get well established in the toenail before you even know it's there.

The fungi that invade nails are called dermatophytes, which means, roughly, fungi that like skin. At the site of infection, usually near the tip of the toe, a fungal colony grows (think of a piece of bread that has gone moldy: each spot of mold is a colony). As the colony gets bigger and better developed, it will start producing spores that can be spread around. They get into socks and shoes, carpets, shower stalls, and bedding. They get spread to other toes, and if conditions are right, they'll set up a new nail fungus infection there. Eventually, they may even spread to the fingernails.

In an advanced nail fungus infection, the toenail gets completely broken down. The fungus has spread throughout the matrix of the nail and digested the keratin so that the toenail becomes thick and flaky, or powdery. Many dermatophytes produce pigments - secretions that are yellow, brown, black, green, and even red (again, think of a really moldy piece of cheese, or fruit and all the colors you may see there). These colors may be visible in the crumbling nail.

The skin around the nail often becomes inflamed as well, because most of the dermatophytes that cause nail fungus infection can infect the skin as well. The skin may become red and irritated looking, or it may just be dry and scaly, looking more like dry skin than an infection. In time, the foot becomes very uncomfortable, and wearing shoes may be extremely painful. Let's hope you don't let your nail fungus infection get to that stage before you seek treatment.