Those fungi that lack a known sexual reproduction cycle are classed as Deuteromycetes. These fungi reproduce only by an asexual process, so far as is known. (When such an organism's sexual stage is discovered, the fungus is usually reclassified.)

Many human pathogens are currently classified as deuteromycetes. These organisms reproduce by fragmenting, with hyphae segments commonly blown about in dust by currents and the wind. A familiar deuteromycete is the fungus of athlete's foot, which can be picked up from fragments on towels and shower room floors.