All about cutaneous fungal infections.

Recognising a cutaneous fungal infection relies above all on observing visible changes in the epidermis, often accompanied by unpleasant physical sensations. The most universal sign is itching, sometimes so intense that it causes scratch-induced lesions. Visually, the infection often presents as redness or local inflammation, but the exact appearance depends on the family of fungi involved. For example, ringworm of the body, which has nothing to do with the herpes virus, forms a rounded red patch with a more pronounced border and a centre that appears to be healing, while “athlete’s foot” results in skin that peels, turns white and eventually cracks between the toes.

The infection can also alter the texture of the skin, leading to peeling or the appearance of small fluid-filled blisters. In skin folds, such as the armpits, under the breasts or in the groin area, the fungal infection often appears as a bright red, moist and sometimes shiny patch, often bordered by small pustules: this is the classic sign of intertriginous candidiasis. Finally, on the scalp, the fungal infection can cause patchy “holes” in the hair where the hairs break off at the root. This is known as ringworm of the scalp.

If you notice a patch that is gradually spreading, that itches, and has a raised surface or scaling, a fungal cause should be strongly suspected.

The development of a cutaneous fungal infection results from an imbalance of the microbiome.

The infection process generally begins with the deposition of microscopic spores on the epidermis, often via infected skin scales left by another person on a damp floor. If the skin barrier is healthy and dry, these spores are naturally eliminated through cellular turnover. Conversely, if they encounter a favourable environment, they germinate and produce filaments called hyphae. These filaments insinuate themselves between the cells of the stratum corneum and secrete enzymes to digest the tissues, thereby triggering the body’s inflammatory response, which manifests as redness and itching. Three main groups of fungi are primarily identified as responsible for skin mycoses:

• Dermatophytes : These fungi are keratinophilic, meaning that they feed almost exclusively on keratin. They never invade deep tissues but spread outwards in a circular pattern on the surface.

• Yeasts, such as Candida : Naturally present in our mucous membranes, they become pathogenic when the microbiota is imbalanced. They are particularly fond of skinfold areas where humidity remains constant.

• The Malassezia : This lipophilic yeast feeds on the fats produced by our sebaceous glands. It is responsible for characteristic pigmented patches on the chest or back.

The underlying cause of the proliferation of these fungi is almost invariably linked to the phenomenon of maceration.

The combination of body heat and humidity, for example linked to sweat or to incomplete drying after a shower, creates an ideal culture medium, as it softens the skin’s protective barrier and facilitates fungal invasion. This is why communal environments such as swimming pools, saunas or gym changing rooms are major sources of contamination: stagnant water on porous floors keeps fungi alive for several hours, waiting for a bare foot to pick them up.

Beyond environmental factors, certain internal elements encourage the development of a fungal infection. A recent course of antibiotics, by eliminating the beneficial bacteria that regulate the population of fungi on our skin, gives these organisms free rein to colonise the available space. Similarly, a temporarily weakened immune system or conditions such as diabetes, which increases the sugar level in tissues – a nutrient yeasts are particularly fond of – promote the establishment of infections. Finally, the use of overly harsh cleansing products alters the natural pH of the skin, destroying the protective acid mantle and making the epidermis much more permeable to external aggressions.

The treatment of a cutaneous fungal infection is based primarily on the use of antifungal agents, whose role is to destroy the fungus and prevent its multiplication.

In the vast majority of cases, a local treatment is entirely sufficient. It is available in the form of creams, gels, sprays or powders to be applied directly to the infected area. Depending on the type of fungus, the doctor or pharmacist may prescribe imidazole derivatives or ciclopirox olamine. The most critical factor for successful treatment is its duration: it is essential to continue the application for the entire prescribed period, often four weeks, even if the visible signs disappear after a few days. Indeed, microscopic spores can survive on the surface and trigger an immediate relapse if the treatment is stopped prematurely.

In more complex situations, such as extensive fungal infections, ringworm of the scalp or infections that do not respond to creams, treatment by oral route may be necessary. These tablets allow the antifungal active substance to circulate in the blood and reach the deeper layers of the skin, hair or nails from the inside. This type of treatment systematically requires a medical prescription and monitoring, as it may involve contraindications or drug interactions. Alongside medicines, the use of specific soaps with a neutral or slightly alkaline pH may be recommended to soothe inflammation and limit the proliferation of yeasts such as Candida, which thrive in acidic environments.

The effectiveness of medical treatment is inseparable from strict hygiene measures to break the cycle of contamination. It is particularly important to keep the infected area completely dry. Thus, after showering, gently pat the skin with a clean towel without rubbing, or use a hairdryer for areas that are difficult to reach, such as skin folds or the spaces between the toes. To avoid re‑infecting yourself, wash your towels, bed linen and socks at a high temperature (at least 60°C) and do not share your personal items. Finally, for fungal infections of the feet, the use of antifungal powders inside shoes can help destroy any spores present and thereby prevent further infectious episodes.

• LORTHOLARY Fungal skin and soft tissue infections. Current Opinion in Infectious Diseases (2016).

• WELSH O. & al. Cutaneous mucormycosis. Anais Brasileiros de Dermatologia (2017).

• PETRIKKOS G. & al. Global cutaneous mucormycosis: A systematic review. Journal of Fungi (2022).

• OSMANCEVIC A. & al. Diagnostic outcomes and treatment modalities in patients with mycosis fungoides in West Sweden—A retrospective register-based study. Cancers (2022).

• EKENG B. E. & al. Cutaneous manifestations of deep mycoses in Nigeria: A systematic review. Therapeutic Advances in Infectious Disease (2024).