The investigation of numerous involved hairs of two patients in a scanning electron microscope reveals that the so-called trichomycosis axillaris is a hair disease of bacterial origin which leads to considerable destruction of the hair cuticle and of the superficial hair cortex. The well-known deposits and yellowish "sheaths" of hairs involved are extensive turf-like or bulbous colonies of myriads of diphtheroid bacteria which proliferate on the surface of the hair destroying the underlying cuticular and cortical keratins. A thready material serves as a "sticky" substance contributing to the adherence of the bacterium on the hair surface, in spite of the mechanical friction of axillary hairs. The observed microorganisms are short, thick, sometimes club-shaped rods, and 0.4μm to 0.6μm × 1.3μm to 1.8μm in size. They correspond to Corynebacterium tenuis, which is considered to be the pathogen micro-organism of the disease. This bacterium is obviously able to destroy keratin.
Orfanos CE, Schloesser E, Mahrle G. Hair Destroying Growth of Corynebacterium tenuis in the So-Called Trichomycosis AxillarisNew Findings From Scanning Electron Microscopy. Arch Dermatol. 1971;103(6):632-639. doi:10.1001/archderm.1971.04000180058008