Nowadays, environmental moulds are often being referred as also being the cause of superficial mycosis. Keratinophilic activity is one of the characteristics involved in the infectious process of some fungal species. With these findings some problems appear: 1) Do these species really act on keratinized tissues?; 2) How do these fungi perform their keratinophilic activity?; 3) Should we validate the results as positives in the case of isolating from the lesions only species considered as environmental? To answer to these questions, the in vitro hair perforation test was performed in 60 different species, including dermatophytes and environmental isolates. In vitro perforation capability, believed to be one of the characteristics involved in some fungal infectious processes, was assessed with aid of optic-, fluorescence-, electron scanning- and transmission-microscopy, followed by calculation of keratinophilic activity. According to Ali-Shtayeh et al., each hair degradation factor has a specific weight in a keratinolytic activity intensity index called “IKA”, which ranges between 0 and 100%. Changes in the hair structure may occur in the two following different ways: (a) Superficial Erosion, where there is an even hair degradation from the outside to the inside (b) Radial Penetration where there is a localized degradation of hair surface, often in a pocket-like structure. Different types of hyphæ are observed: of narrow diameter called boring hyphæ, of larger diameter called wider boring hyphæ) and swollen boring hyphæ (with dilated tips). Hyphæ may also produce highly specialized perforation organs.