Cutaneous Mycoses

Cutaneous mycoses are a group of superficial fungal infections affecting the skin and its appendages, including the hair and nails. The term mycoses generally refer to infections caused by fungi, also known as mycetes, while cutaneous refers to the involvement of the skin.  

Fungi are a diverse group of living organisms that can be found nearly everywhere: in the environment, parasitizing animals and plants; in the soil; and on and inside the human body. Normally, the fungi that live on the skin’s surface are relatively harmless, but in certain cases, they may grow out of control or penetrate the skin through a wound, causing an infection.  

Since fungi thrive in warm, moist environments, cutaneous mycoses are more likely to affect the feet, groin, armpits, and other skin folds; body areas that are favorable for fungal growth. Additionally, certain environmental conditions (e.g., warm and humid climates, crowded places, communal showers, locker rooms) can provide an excellent breeding ground for the growth and spread of many fungal diseases.  

Mycoses can be broadly classified as superficial, cutaneous, subcutaneous, and systemic based on their degree of invasiveness.   

Superficial and cutaneous mycoses are both caused by fungi that affect the superficial layers of skin, hair, and nails. The main difference between them is that superficial mycoses cause little or no inflammation, whereas cutaneous mycoses generally trigger an inflammatory response that causes skin redness and itching.  

Subcutaneous mycoses are localized infections of the skin and underlying tissue that usually result from a cut or puncture wound to the skin (e.g., from a rose thorn). The opening in the skin allows fungi from the environment to enter the skin and gain access to deeper tissues.  

Finally, systemic mycoses affect internal organs (e.g., lungs, brain, gastrointestinal tract) and are generally caused by opportunistic fungi. These microbes are typically harmless for healthy individuals, but they can take advantage of an opportunity, like a weakened immune system, to cause an infection.  

There are several types of fungal infections of the skin. Most cutaneous mycoses are caused by dermatophytes, a group of filamentous fungi that colonize and infect keratinized tissues, including the outermost layer of skin (i.e., stratum corneum), hair, and nails. Dermatophytes are commonly found in the environment and are spread from one person to another through direct skin contact or, more rarely, through contact with an infected animal or soil. Although there are a number of dermatophyte species, most dermatophyte infections are caused by fungi of the Trichophyton, Microsporum, and Epidermophyton genera.  

Dermatophyte infections of the skin are commonly called tinea, or ringworm. Specific examples include tinea corporis (i.e., ringworm) which affects the arms, trunk, and legs; tinea capitis (i.e., scalp ringworm) affects the scalp and hair shafts; tinea cruris (i.e., jock itch) affects the groin area and inner thighs; and tinea pedis (i.e., athlete’s foot) affects the feet and toenails.  

In addition to dermatophytes, cutaneous mycoses may also be caused by yeasts of the Candida genus. Candida is naturally present on the skin and mucous membranes. When the amount of Candida is low, it is harmless, but when it starts to overgrow, it can damage the skin and nearby tissues, resulting in a superficial skin infection. A weakened immune system is often the reason for Candida overgrowth. As a result, candidiasis typically affects individuals with immunosuppressive conditions (e.g., diabetes, HIV infection), who are more vulnerable to opportunistic infections. 

More rarely, cutaneous mycoses can be due to infection by non-dermatophytic fungi, like an Aspergillus species. Aspergillus is a family of molds consisting of many different species, some of which can cause a condition known as aspergillosis. Cutaneous aspergillosis is a rare form of locally invasive disease that typically occurs when invasive aspergillosis spreads to the skin from somewhere else in the body, such as the lungs especially in immunocompromised individuals. Primary infection of the skin, such as after surgery, trauma, or burn wound, may also occur but is much less common. 

Signs and symptoms of cutaneous mycoses vary depending on the infectious agent, location of the infection, and severity of the infection.  

Tinea infections often present with an itchy rash that has a central clearing surrounded by an inflamed, scaly border. These lesions have a characteristic ring-like appearance because they tend to grow in an outward pattern. Despite its characteristic appearance, tinea may still be difficult to distinguish from other cutaneous mycoses, including Candida infections.  

Cutaneous candidiasis often presents as red skin patches with small satellite lesions that usually affect skinfold areas (e.g., armpits, groin, under the breasts). Candida can also affect the nails, causing them to harden and turn yellow.  

Finally, cutaneous aspergillosis can present with distinctive skin wounds, known as eschars, in the affected area. 

Many cutaneous mycoses can be diagnosed by their clinical appearance upon physical examination. However, if the diagnosis is unclear, it may be confirmed with additional diagnostic tests, including Wood’s lamp examination, direct microscopy, fungal cultures, and molecular assay.  

 A Wood’s lamp uses ultraviolet light to detect areas of fluorescence caused by fungus, that is otherwise invisible to the naked eye. Microscopic observation of skin scrapings, hair, or nails is often performed to detect the presence of fungi. The samples are usually prepared with a potassium hydroxide (KOH) solution that dissolves the keratin found in tissues, so the branching filaments of the fungi (hyphae) or fungal spores can be seen under the microscope. For diagnosis of nail infections, periodic acid-Schiff (PAS) stains can be useful for visualizing fungal hyphae and spores within the nail clipping.  

In individuals who do not respond well to initial treatment, a fungal culture can be done. Fungal specimens are often grown on a Sabouraud dextrose agar plate, a growth medium that supports fungal growth while limiting the growth of most bacteria. Finally, molecular assays, such as polymerase chain reaction (PCR), are useful in the diagnosis of fungal infections.  

Treatment of cutaneous mycoses varies depending on the underlying cause of infection. In general, most cutaneous mycoses require treatment with antifungal medications (e.g., azole antifungals, amphotericin, terbinafine). Nystatin is an anti-fungal that is commonly used to treat Candida infections but is ineffective against tinea. Aspergillosis is often responsive to the anti-fungal medication, voriconazole. Antifungal medications may be topical or oral, and the type recommended generally depends on the severity of the infection or the part of the body affected. For example, treatment of tinea capitis involves both oral medications and sporicidal shampoos (e.g., selenium sulfide, ketoconazole).  

Additional measures that can help prevent repeated fungal infections include following treatment recommendations closely, practicing good hygiene, wearing clothing that allows air circulation next to the skin, and keeping the skin clean and dry. Of note, using corticosteroid creams on fungal infections can worsen the rash, thus these medications are generally avoided once a diagnosis is made.