Common Infections of the Foot and Toes

Identifying and Treating Bacterial and Fungal Infections

A common presentation of athletes foot (tinea pedis). Getty Images

No matter how clean your feet are, they are constantly in contact with the bacteria and other organisms that can cause infection. In most cases, our immune system can keep these pathogens at bay, but there are times when our immune defenses are breached either by an injury that breaks the skin or direct contact with a fungus, perhaps picked up at the gym.

Toenail Infections

Bacterial infections beneath or adjacent to a toenail usually occur when there has been some sort of trauma.

This happens most commonly when an ingrown toenail (onychocryptosis) punctures the skin surrounding the nail. Ingrown toenails develop frequently on the big toe and are often caused by the shape of the toe, bunions, or wearing loose socks which can catch burrs on the edge of the nail.

When a bacterial infection occurs, the surrounding skin will become red, swollen, and painful. There may even be a yellow or greenish discharge in the form of pus. The most common bacterial culprit is Staphylococcus aureus which can be treated with an over-the counter antibacterial cream and/or by soaking the foot in an Epsom salt solution using room temperature water.

Fungal infections are also common and can directly impact the toenail itself. The infection, known as onychomycosis, is slow-growing and most often spreads beneath the nail. Symptoms include the thickening of the nail accompanied by brown or yellow discoloration, flaky debris under the nail, and/or separation of the nail from the nail bed.

Onychomycosis is notoriously difficult to treat since most topical creams can't penetrate the nail tissue. Oral antifungal treatment tends to work best but can take as much as six to 12 months for a nail to fully grow back. Terbinafine is considered the treatment of choice, often supported by itraconazole, another oral antifungal.

Infection Between the Toes

When a rash, itchiness, and flaking develops between the toes, it is most often related a fungus called tinea pedis and the all-too-uncommon condition known as athlete's foot. The fungus thrives in moist environments such as gyms and saunas and can flourish in sweaty socks and shoes. Mild cases can be treated with an over-the-counter antifungal cream or spray. More serious infections may require oral medications such as terbinafine or itraconazole for a period of two to six month.

One type of bacterial infection frequently mistaken for a fungus is erythrasma. Erythrasma is caused by the bacteria Corynebacterium minutissimum and is most commonly seen in diabetics and the obese. The patches of infection between the toes are initially pink but quickly become brown and scaly as skin starts to flake and shed. Erythrasma is best treated with a topical fusidic acid cream or an oral antibiotic such as azithromycin or erythromycin.

Foot Abscess

Bacterial infections of the feet can result in the consolidation of pus beneath the skin known as an abscess. An abscess of the foot is most often caused by a puncture wound (such as can happen with an unsterile pedicure) or the infection of a hair follicle.

These types of infections appear red and abnormally swollen, and can sometimes be mistaken for an insect bite in the early stages. S. aureus is again the most likely cause, although other bacterial types may be involved. Treatment usually involves the drainage of the abscess as well as the use of antibiotics.

Cellulitis

Skin infections of the foot can sometimes resemble a rash. One such instance is a type of bacterial infection called cellulitis. Cellulitis typically appears as a small area of pain and redness which quickly spreads to surrounding tissues, causing the formation of characteristic red streaks moving upward from the foot.

These streaks, known as lymphangitis, are an indication that the infection is migrating toward the lymph nodes. Cellulitis is typically caused by a break in the skin but is especially common in people with diabetes or those with poor circulation. S. aureus and streptococcus are the most likely causes.

The development of cellulitis with lymphangitis requires prompt medical treatment to avoid further spread of infection. If left untreated, the infection can disseminate to deeper tissues, including the bones. A 14-day course of antibiotics is usually enough to treat an uncomplicated infection. Serious ones may require intravenous therapy.

Sources:

Findley, K.; Oh, J.; Yang, J.; et al. "Topographic diversity of fungal and bacterial communities in human skin." Nature. 2013; 498:367-370.

National Health Service (UK). "Foot problem: a visual guide." London, England; updated July 27, 2016.

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