The infected hairs of tinea capitis due to Microsporum canis: demonstration of uniqueness of the hair cuticle by scanning electron microscopy.

Scanning and transmission electron microscopic studies were done on scalp hairs of four patients infected with ectothrix Microsporum canis. Both freeze fracture and cross-sectioning of hairs revealed a thick sheath of fungal spores encircling the hair shaft beneath an intact cuticle. These spores were not visible on surface inspection but became apparent only where the cuticle had been rubbed off or broken. Daily selenium sulfide shampoos removed all of the spores from these sites. The cuticle is viewed as being an effective barrier to the penetration of fungi, so that the hair is vulnerable to fungus infection only deep within the hair follicle below the level of the mature cuticle. Once the fungus enters the hair cortex just above the hair bulb, it produces myriads of spores that remain trapped and hidden beneath the cuticle for the length of the intact hair.