No matter how clean your feet are, they're constantly in contact with the bacterial world, so it's easy to see why they would be susceptible to infection. Whether we're barefoot or wearing shoes, there's no escaping exposure to bacteria that can cause an infection. In most cases, our immune system keeps these pathogens at bay, but occasionally, things such as an ingrown toenail or a tiny puncture wound can set the stage for a bacterial infection.
Common Foot Infections
Toenail Infections. Bacterial infections surrounding toenails usually occur when there has been some kind of trauma to the skin beneath, or adjacent to, the nail. Most often, it's an ingrown toenail of the big toe that leads to an infection. An ingrown toenail occurs when the edge of the toenail presses into adjacent skin, usually puncturing it, which creates pain—and sometimes infection. Symptoms of an infected ingrown toenail include red, swollen, and painful skin on the side of the toenail. Sometimes, yellow or greenish drainage occurs.
Blunt or repeated trauma to a toenail can also lead to an infection. Common examples of trauma are a crushing-type injury to a toe, or athletic activity that causes rubbing of the nail against the shoe. In these cases, an infection may develop along with a loose or black toenail that occurred from the trauma. Regardless of the cause of the infection, the most common bacterial culprit in a toenail infection is staphylococcus aureus, also known as staph.
Infections Between Toes. When a rash or wound develops between toes, there are a few possible causes. In most cases, the cause is a fungal infection—the same organism that causes athlete's foot. Another cause is a bacterial infection, which is one reason that some foot infections don't seem to heal with anti-fungal creams. One type of bacterial infection that is frequently mistaken for a fungus is called erythrasma. Unlike athlete's foot, this is treated with an antibiotic.
Abscess. Bacterial infections of the feet can occur as collections of pus, such as an abscess, from a puncture wound or an infected hair follicle. These types of infections are usually red and elevated, and sometimes can be mistaken for an insect bite. There are many types of bacteria that cause an abscess, but staph are a leading cause. Medical treatment usually involves drainage of the lesion, as well as antibiotics if indicated. The drainage may be sent to a laboratory in order to determine the types of bacteria causing the infection.
Cellulitis. Skin infections can also resemble a rash, appearing as a reddened, tender, and warm area of skin. This type of infection is called cellulitis and can spread quickly, leading to red streaks that move from the foot toward the leg. The appearance of streaks is known as lymphangitis, which means the infection is spreading toward the lymph nodes. Cellulitis and lymphangitis can be caused by a variety of types of bacteria, but staph and sometimes streptococcus (strep) are the most common causes. Any infection, especially cellulitis and lymphangitis, requires prompt medical attention to avoid further spreading and complications. If left untreated, some infections can spread to deeper tissues, including bone.
Certain health conditions can increase susceptibility to foot infections. The most well-known example of this is diabetes, which in some cases can lead to slow or non-healing wounds of the feet. These wounds have the potential to become infected, increasing the risk of hospitalization and the need for limb amputation. To learn more, see: How Diabetes Can Affect Your Feet.
Dockery, DPM, Gary L. and Crawford, DPM, Mary Elizabeth (Ed.). Cutaneous Disorders of the Lower Extremity. Philadelphia: W.B. Saunders, 1997. 35-40.