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Favus

Trichophyton schoenleinii

For medical students2 min readUpdated 2026-10-10

Favus (tinea favosa) is a chronic anthropophilic fungal infection caused by the dermatophyte Trichophyton schoenleinii. The pathological process predominantly affects children, localizing to glabrous skin, the scalp, and nail plates, and is accompanied by the formation of specific structures.

Causative agentTrichophyton schoenleinii
LocalizationSkin, hair, nail plates
Pathognomonic signYellow scutulum (crust)
CultureGrowth showing "chandelier" and "staghorn" hyphae

Clinical and Epidemiological Characteristics

The disease known in classical medicine as favus is a classic anthropanthroponosis, meaning the source of infection is exclusively human. The highest-risk group primarily includes children, whose immune system and skin barrier functions are still developing. This pathology has a pronounced chronic character, requiring prolonged medical follow-up.

The main localization of the pathological process involves several anatomical zones simultaneously. The pathogen is capable of actively colonizing and destroying:

An absolute pathognomonic clinical sign of favus development is the formation of the so-called scutulum (plural: scutula). Visually, it is a characteristic bright yellow formation. Histologically and microbiologically, the scutulum is a complex conglomerate. Detailed examination reveals a massive accumulation of fungal spores, intertwined mycelial threads, desquamated cells of the affected epidermis, and lipid elements.

Microscopic Diagnostic Features

Laboratory verification of the diagnosis is based on careful microscopic examination of biological material collected from the patient. The picture varies significantly depending on the substrate being analyzed.

  1. Examination of skin scales. When examining scrapings from glabrous skin under a microscope, a specific picture is visualized: branching mycelium with clearly defined septa is detected. In addition, arthrospores are present in this material, indicating an active process of hyphal fragmentation.
  2. Hair examination (favus type). Hair shaft involvement in favus has unique specifics designated in mycology as the "favus type". The key feature is the localization of fungal elements strictly inside the hair itself. Microscopy within the thickness of the hair shaft reveals not only septate mycelium and dense clusters of spores, but also characteristic gas bubbles, the appearance of which is an important diagnostic marker for this specific pathogen.

Cultural Properties of the Pathogen

When isolating a pure culture of Trichophyton schoenleinii on nutrient media, the mycologist evaluates the characteristic morphological features of fungal growth. The vegetative body (mycelium) of the pathogen is septate, meaning it is divided into separate cellular compartments.

Special attention is paid to the shape of the hyphae. Favus mycelium typically shows specific thickenings and abundant branching. These morphological changes lead to the formation of structures that have received descriptive names in laboratory practice:

Spore formation in culture is represented by several types of elements. Arthrospore mycelium forms, protective chlamydospores appear, and large macroconidia are produced. The dimensions of macroconidia average 8 × 50 µm, serving as an important morphometric parameter for identification.

Mnemonic

Picture a STAG (staghorn hyphae) holding a CHANDELIER, wearing a yellow SHIELD (scutulum), while GAS BUBBLES (favus hair type) tangle in its hair.

Frequently asked questions

What laboratory diagnostic methods are used to verify favus?

Microscopic, mycologic, and several additional methods are used to verify favus.

  • Microscopic method — rapid diagnosis of clinical material (scrapings, hair, nails) after treatment with a 10–15% KOH solution. In favus, fungal elements and gas bubbles are detected inside the hair.
  • Mycologic method — inoculation onto nutrient media for species identification based on growth characteristics.
  • Serological method — detection of specific antibodies using complement fixation, indirect hemagglutination, precipitation, direct immunofluorescence, or ELISA.
  • Allergy testing — intradermal skin tests with fungal allergens.
  • Biologic assay — inoculation of laboratory animals (mice, guinea pigs) in the skin, nails, or hair.
On what elective nutrient media is Trichophyton schoenleinii cultivated?

Specialized mycological nutrient media are used to cultivate the favus pathogen.

  • Sabouraud agar — the primary elective medium for fungal isolation.
  • Wort agar — an additional medium for plating clinical material.

Inoculation is performed using mycological (cultural) methods. Incubation is carried out at 25 °C, and the growth duration ranges from 1 to 3 weeks. The purpose of cultivation is species identification of the pathogen based on its growth characteristics on these media.

What sign is considered pathognomonic for favus?

An absolutely specific sign is the formation of a yellow scutulum (crust) consisting of spores, mycelium, lipids, and epidermal cells.

What is the specific feature of hair involvement in the "favus type"?

In the "favus type," fungal elements (septate mycelium, spore clusters) are located inside the hair shaft, which is also characterized by the formation of gas bubbles.

What specific mycelial forms are identified during cultivation?

The culture of Trichophyton schoenleinii is characterized by branching mycelium with thickenings forming "chandelier" and "staghorn" shapes.

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