Infection can be caused by a number of different agents. Athlete's foot is an infection of the skin caused by a fungus. Warts are caused by a viral infection of the skin. When most people think about infections they are thinking about infection caused by bacteria. There are numerous types of bacterial infection. Infection generally requires a break in the skin from a cut, abrasion, puncture wound or ulceration. The most common infection is caused two bacteria, Staphylococcus and Streptococcus. Both of these infections cause progressive tissue damage of varying degrees. People with diabetes can develop infections by several bacteria at the same time.

Infection that occurs in the skin is called cellulitis. Deep infections that develop puss pockets are called abscesses. The most common bacterium that causes cellulitis is Streptococcus. These infections can become very serious and even life threatening. Cellulitis is characterized by spreading redness in the area with an increase in the temperature of the skin, often accompanied by fever and chills. People who suffer from venous stasis, chronic swelling in the legs, are prone to these infections. Cellulitis is also commonly seen in associated with athlete foot conditions. The athlete's foot causes small breaks in the skin, which can become infected, by the Streptococcus bacteria. Soft corns, particularly between the fourth and fifth toes can also become infected and cause cellulitis and or an abscess. Puncture wounds are very likely to become infected. This can result in a very dangerous deep abscess that can also infect the bone. A doctor should evaluate all deep puncture wounds as soon as possible. Simply cleaning the outside of the puncture wound is not enough to prevent infection. Oral antibiotics should be prescribed and the wound watched carefully. If there is any sign of infection, surgical cleaning of the wound should be preformed.

People with diabetes are at particular risk of infection. In fact, people with diabetes spend more time in the hospital for foot infections than for any other reason. Corns and calluses on the feet of people with diabetes can break down and allow bacterial invasion of the tissue. In people with long standing open ulceration the underlying bone can become infected. Bone infections, called osteomyelitis, generally require surgery to remove the infected bone. These infections are very difficult to cure with oral or intra-venous antibiotics without also removing the infected bone. The presence of bone infection can be diagnosed with special tests such as bone scans, CT scans and MRI. These test are not 100% accurate however and the experience of the treating doctor becomes very important in making the correct determination as to the presence of bone infection.

Gout, which is caused by an elevated blood uric acid level, can be confused with infection. This condition can cause sudden onset of pain, redness, and swelling of a joint or in the soft tissues. It is important to rule out an infection, particularly if it is in a joint. Rare instances of infection can occur without evidence of a break in the skin. The infection is carried to the site by the blood stream. Close examination of the patient may reveal an abscessed tooth that likely is the source of the infection. In other instances no source of the infection can be found.

People who have joint replacements, heart valve replacements or who have a pacemaker must be very cautious regarding infections. They are at risk of an infection spreading from another site to the area of their joint replacement, heart valve replacement or pacemaker. Also, people who have mitral valve prolapsed must be cautious if they have infections because the infection can spread to the heart.