Mould spores: the unusual suspects in hay fever.

Microfungi are microscopic plants that lack chlorophyll and depend on plant or animal material for nourishment. Moulds will only proliferate in a humid atmosphere. Moulds produce vast numbers of small spores, varying in diameter from 2 to 5 microns, which become airborne. Some common moulds in the UK include Cladosporium, Alternaria and Aspergillus, of which several species are pathogenic to humans. The frequency of mould allergy is uncertain, but it appears to be higher in children than in adults. Wet weather favours mould growth, and sunny, windy weather favours spore release, while snow reduces both considerably. In warm, humid climates, fungi are present in large quantities all the year round. In temperate zones, spore counts are highest during the late summer. Indoor exposure largely depends upon the level of humidity. Mould growth can be immense in badly constructed houses and can contribute to sick-house syndrome. Occupational exposure can occur during manufacture of bread, cheese, beer and wine. In recent years, the use of moulds has been extended to include antibiotic, enzyme and steroid manufacture. Inhalation of small quantities of mould spores can evoke an IgE response and asthma. Massive exposure to some moulds growing in the airway can evoke an IgE and IgG response in people with bronchopulmonary aspergillosis. The inhalation of large amounts of mould antigen in organic dust can cause an IgG response and extrinsic allergic alveolitis