There are no set levels of airborne fungi, which can be regarded as safe. Much depends on the out door concentration and also depends on the types of spores present indoors. Each office, each, building, or each home must be considered as a separate and unique case. A small group of fungi are also human pathogens. While many human pathogens just cause mild or annoying conditions, such as athlete's foot and ringworm, other human pathogens can cause severe and debilitating diseases.
Some fungi produce mycotoxins, which can be present within the spores and inhaled with the spores.
Mycotoxins are potent compounds. Many are carcinogens, and others can impare the immune system. There has been a great deal of interest in the past few years on mycotoxins in indoor air. Occurs indoors in wet environments on a variety of substrates. Considered allergenic but not well studied.