Aspergillus oryzae is an asexual, ascomycetous fungus used for hundreds of years in the production of soy sauce, miso and sake without recorded incidents. There are conflicting opinions about whether A. oryzae can be isolated in nature. Although the details of the genetic relationship between A. oryzae and A. flavus remain unclear, the two species are so closely related that all strains of A. oryzae are regarded by some as natural variants of A. flavus modified through years of selection for fermenting of foods. A. oryzae is regarded as not being pathogenic for plants or animals, though there are a handful of reports of isolation of A. oryzae from patients. There are also several reports of products of A. oryzae fermentations, e.g. a-amylase, that seem to be associated with allergic responses in certain occupations with high exposure to those materials. A. oryzae can produce a variety of mycotoxins when fermentation is extended beyond the usual time needed for production of these foods. While wild A. flavus isolates readily produce aflatoxins and other mycotoxins, A. oryzae has not been shown to be capable of aflatoxin production.