Fungal infections are an important public health problem due to their high prevalence worldwide (20–25% of the population is infected); dermatophytes of the Microsporum, Trichophyton, Epidermophyton, and Candida genera are the most common pathogens. The nature and frequency of detection of this pathology is influenced by the climate in a particular region and the socio-economic status of the population. Dermatomycetes lead to damage to nails, skin of the feet and hands, scalp, smooth skin and folds. Infection is possible through contact with a sick person or animal, or with the patient’s personal belongings. Risk factors include damage to the integrity of the skin, increased sweating or dry skin, changes in skin pH, and poor hygiene. However, the main reason for contamination with dermatomycetes is the presence of chronic diseases of the endocrine, cardiovascular, circulatory systems, metabolic and oncological diseases. Long-term use of systemic and local glucocorticosteroid drugs (GCS), cytostatics, irrational antibacterial therapy; the presence of the human immunodeficiency virus, smoking, and heavy physical labor contribute to the chronicity of fungal infection, poor response to antifungal therapy, and can cause a recurrent course. Also in practice, there are often cases of modification of the clinical picture of dermatophytosis as a result of the influence of the above factors and incorrect therapy. The article discusses the clinical case of a patient with late diagnosis of mycosis of smooth facial skin, developing against the background of diabetes mellitus and long-term use of local combined corticosteroids. Possible causes, differential diagnosis with other dermatoses and methods for diagnosing the “transformed” variant of microsporia (Tinea incognito) are also outlined. Successful diagnosis and effective treatment with local and systemic terbinafine led to the patient’s recovery and avoided the development of complications. Terbinafine has shown high efficacy, safety, local availability, and ease of use, which increases the likelihood of treatment compliance and patient’s and physician adherence to treatment.

Keywords: microsporia, dermatophytosis, terbinafine