Some Aspergillus species cause serious disease in humans and animals. The most common pathogenic species are A. fumigatus and A. flavus , which produces aflatoxin which is both a toxin and a carcinogen, and which can contaminate foods such as nuts. The most common species causing allergic disease are A. fumigatus and A. clavatus . Other species are important as agricultural pathogens. Aspergillus spp. cause disease on many grain crops, especially maize , and some variants synthesize mycotoxins , including aflatoxin. Aspergillus can cause neonatal infections .