Fungal infections of the skin on the feet are common. Most are due to one type of fungal infection but other less common and even rare fungi can also cause infections of the feet. For example, thrush is caused by Candida albicans, a type of yeast, and this fungus can also infect the skin on the feet. However, “thrush of the foot” is rare. There are several reasons why fungal infections are more likely to occur on the feet. Understanding why this may occur on the feet in particular can help to prevent future infections after treatment.
Types of Fungal Foot Infections
Although fungi are in one kingdom of organisms, there are man different families and species of fungi. Most fungal infections of human skin, whether on the foot or elsewhere on the body, are caused by dermatophytes. Less commonly, yeasts can also infect human skin. The Candida species of yeasts are the main cause of these type of skin infections but another rare yeast can also cause an infection of the skin on the feet, particularly on the soles.
The term dermatophytosis refers to skin infections caused by dermatophytes. It also includes dermatophyte infections of hair and nails. Dermatophytes are one type of fungi that have a predilection for human skin. These fungi contain enzymes which can digest keratin, the protein that forms the outer layers of the skin. Dermatophytes are the most common type of fungi to cause fungal skin infections.
Yeast infections of the skin are far less common although this type of fungi cause infections of the vagina and mouth which are referred to as vaginal thrush and oral thrush, respectively. The main yeast to infect humans is Candida albicans. Skin infections by this species of yeasts is known as cutaneous candidiasis. It is more likely to occur when the skin is broken and particularly at folds of skin, like between the toes of the feet.
Tinea nigra is a type of fungal skin infection that mainly affects the palms of the hand and soles of the feet. It is a rare fungal infection mainly caused by a specific species of yeast. This is not the Candida species of yeast as is therefore not discussed under cutaneous candidiasis. A characteristic feature of tinea nigra infection is that it causes a dark brown to black spot or patch at the site of the infection.
Pictures of Fungus Foot Infections
Causes of Fungal Feet Infections
Fungi are found throughout the globe and are widely prevalent in the environment. It is found in the air, on surfaces, on humans and other animals, as well as in the soil. Some fungal species are more common than others and yeasts like Candida may naturally occur on human skin. Although people come into contact with fungi on a constant basis, this does not usually lead to an infection.
The skin is physical barrier that can prevent a fungal infection from arising if it is healthy. Similarly the cavities like the mouth are able to prevent an infection if there is the correct balance of other microorganisms present within it. The immune system will also keep fungi from causing an infection. However, these mechanisms are not always functioning properly or sufficient to prevent an infection from fungi in every instance.
Furthermore, fungi need certain environmental conditions to thrive. It prefers moist areas, such as the feet and groin. Warmth is another factor that helps fungal growth. A break in the skin increases the risk of a fungal infection. Some people may have a genetic susceptibility to fungal skin infections. There is also a greater risk if there close skin-to-skin contact with a person who has an infection. Even sharing items and facilities can spread the fungi.
The most common fungal infection of the foot, known as tinea pedis or athlete’s foot, is usually caused by the dermatophyte Trichophyton rubrum. Other fungi such as Trichophyton interdigitale and Epidermophyton floccosum are also responsible for athlete’s foot. It may occur anywhere on the skin of the feet.
The risk of contracting this infection is greater in regions that are hot and humid. Sharing personal items like towels and footwear as well as using common facilities like showers also increase the risk of athlete’s foot spreading from one person to another. Certain fungal species in the soil and on animals can be spread to humans.
Read more on athlete’s foot.
Foot Candida (Thrush)
Candida albicans is the most common yeast to cause fungal infections of the skin on the feet. This species of fungi is widespread in the environment as well as in cavities such as the mouth. It may naturally occur on the skin folds in some people but this may not always cause an infection at the site.
It is more likely to lead to an infection where there is a break in the skin, as is the case with repeated injuries and chaffing or even with athlete’s foot. The term thrush is used to describe Candida infection of cavities, such as the mouth (oral thrush) or vaginal (vaginal thrush).
Read more on cutaneous candidiasis.
Black Fungus on Soles
Tinea nigra is caused by a species of fungus known as Hortaea werneckii (also known as Exophiala werneckii and Phaeoannellomyces werneckii). It damages the skin and concentrates the natural skin pigment known as melanin. Since melanin is a brown color, the affected patch appears dark brown to black in color.
The fungus responsible for tinea nigra has a predilection for areas with a high concentration of eccrine sweat glands. These glands are most dense on the palms and soles. There the characteristic dark brown to black patch on spot in tinea nigra is mainly seen on the soles of the feet. It usually does not cause any itching or pain.
The tinea nigra fungi is uncommon in the United States. It is more likely to affect people who live in tropical regions of Central and South America, Africa, and Asia