To the Editor:
Dermatophytes are keratinophilic fungi in the family Arthrodermataceae that infect keratinized tissues, such as skin, hair, or nails, causing dermatophytosis (tinea). They are among the most frequent infectious agents encountered in dermatology.1 Conventionally, dermatophytes were grouped into three genera – Tricophyton, Microsporum, and Epidermophyton – based on morphological features.2 However, significant taxonomic revisions in recent years have expanded and reorganized this classification.3 In consequence, lack of awareness of these updates may contribute to diagnostic ambiguity and potentially to therapeutic delay. The purpose of this letter is to highlight the updated phylogenetic classification of dermatophytes and to outline its relevance in current clinical practice.
It is increasingly recognized that morphological traits alone do not reliably reflect evolutionary relationships.4 This principle has also become evident in dermatophytes. Multilocus sequencing has led to the establishment of a revised taxonomy that includes additional genera: Arthroderma, Lophophyton, Nannizzia, Guarromyces, Paraphyton, and Ctenomyces.3,5
Classification of dermatophytes according to ecological niche remains scientifically relevant. Anthropophilic species are typically associated with chronic and minimally inflammatory infections, while zoophilic and geophilic dermatophytes more often produce acute and inflammatory clinical manifestations. Therefore, accurate species identification is not only epidemiologically informative, but also relevant for therapeutic decision-making in selected clinical contexts, particularly in inflammatory disease, zoonotic infections, or treatment-refractory cases (Table 1).3,5–7
Table 1. Clinically relevant dermatophyte genera according to ecological niche and commonly encountered species
| Genus | Ecological niche | Examples |
|---|---|---|
| Tricophyton | Anthropophilic (+++), Zoophilic | Trichophyton rubrum, Trichophyton mentagrophytes, Trichophyton interdigitale, Trichophyton tonsurans |
| Epidermophyton | Anthropophilic | E. floccosum |
| Microsporum | Zoophilic (+++), Anthropophilic | Microsporum canis, Microsporum audouinii |
| Nannizzia | Geophilic | Nannizzia gypsea, Nannizzia incurvata |
| Arthroderma | Geophilic (+++) | Arthroderma benhamiae, Arthroderma vanbreuseghemii |
| Lophophyton | Zoophilic | Lophophyton gallinae |
| Guarromyces | Not fully established* | Guarromyces ceretanicus |
| Paraphyton | Not fully established* | Paraphyton cookie |
| Ctenomyces | Geophilic | Ctenomyces serratus |
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* Ecological classification reflects predominant associations described to date. For Guarromyces and Paraphyton, ecological data remain incompletely characterized. |
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Despite these changes, Tricophyton species remain the most common cause of human dermatophytosis. Within this revised taxonomy, Trichophyton indotineae, formerly belonging to the Trichophyton mentagrophytes/Trichophyton interdigitale complex has emerged as a distinct lineage associated with widespread and recurrent tinea that is now increasing globally. This species has been associated with treatment failure, particularly in regions where terbinafine resistance has been documented.8 Furthermore, itraconazole resistance and heteroresistance have also been documented, emphasizing the relevance of species-level diagnosis and antifungal stewardship.9
It is imperative that dermatologists remain updated in dermatophyte taxonomy, particularly in the context of globalization, which has contributed to an increasing number of dermatophytosis cases with distinct clinical behavior depending on the species involved.6 This revised taxonomy provides more accurate species identification and strengthens public health surveillance strategies. Despite the absence of clearly defined clinical antifungal breakpoints for dermatophytes, species-level identification may still support rational antifungal treatment selection in selected clinical contexts.
We therefore encourage the routine adoption of the updated classification into laboratory reporting and clinical education.
Funding
None.
Conflicts of interest
None.
Ethical considerations
Protection of human subjects and animals. The authors declare that no experiments on humans or animals were performed for this research.
Confidentiality, informed consent, and ethical approval. This study does not involve personal patient data, medical records, or biological samples, and does not require ethical approval. SAGER guidelines do not apply.
Declaration on the use of artificial intelligence. The authors declare that no generative artificial intelligence was used in the writing or creation of the content of this manuscript.
