Cellulitis is defined as an infection of the skin, typically by bacteria. Bacteria are microscopic organisms that can enter the body, multiply rapidly using the body's chemicals as a food source, and spread. They release toxic chemicals which can cause local tissue damage as well as possible organ damage if they spread through the blood stream. Cellulitis can affect a wide range of people, from those that are very healthy all the way down to those with poor or compromised immune systems. In such an infection, the body's defenses are overwhelmed, and the bacteria are able to rapidly reproduce and spread. People with diabetes, those on immune suppressants for organ transplants or auto-immune diseases, and those with diseased immune systems such as seen with HIV are at particular risk for these infections.

The bacteria in cellulitis can enter the body through a number of ways. The skin typically acts as a barrier to bacteria, and when the skin is compromised, the bacteria have an entry portal into the body. In the foot, this usually takes place through a skin wound (ulcer), a puncture wound or cut, cracks and fissures in dry skin, fissures in between the toes, or along side an ingrown nail. Once inside the body, the bacteria spreads. The body's immune system begins to fight this infection, and the resulting reaction creates redness, warmth, and swelling at the site of infection, sometimes with internal pus as a byproduct. If the body cannot keep the infection contained, it will spread up the skin. In the foot, this can be seen as a red streak progressing toward the ankle and leg, although sometimes it has no external sign. As the infection spreads, lymph nodes in the leg can become swollen and tender. If the bacteria reach the blood stream, they can circulate through the body and cause organ damage. The toxins created by the bacteria once in the blood stream can cause shock and can be potentially life threatening.

CellulitisTreatment of cellulitis varies according to the severity of the infection. Light or moderate cases, such as with an ingrown toenail, a wound, or a superficial abscess can be easily treated with typical oral antibiotics. Infections in diabetics or those with poor immune systems will need antibiotics that cover a wide range of bacteria. If a fluid culture is possible the bacteria can be identified and the antibiotic can be narrowed down further. More serious infections, or ones that are not improving with oral antibiotics will need intravenous antibiotics and possibly hospitalization. The most serious infections require hospitalization in a special isolated room as to prevent spreading the infection to others, along with potent antibiotic therapy for an extended period.