Aflatoxin is a naturally occurring mycotoxin produced by two types of mold: Aspergillus flavus and Aspergillus parasiticus. Aspergillus flavus is common and widespread in nature and is most often found when certain grains are grown under stressful conditions such as drought. The mold occurs in soil, decaying vegetation, hay, and grains undergoing microbiological deterioration and invades all types of organic substrates whenever and wherever the conditions are favorable for its growth. Favorable conditions include high moisture content and high temperature. At least 13 different types of aflatoxin are produced in nature with aflatoxin B1 considered as the most toxic. While the presence of Aspergillus flavus does not always indicate harmful levels of aflatoxin it does mean that the potential for aflatoxin production is present.