Fungi are known to be causative factors that induce asthmatic symptoms. Outdoor airborne fungi, including Cladosporium, Alternaria, Penicillium, and Aspergillus are significant triggers of IgE formation, as are the indoor fungi Aspergillus, Neurospora, and Eurotium. In addition, some practitioners believe there is a strong fungal/yeast component in the lung and/or gut microflora in individuals with asthma.