So what situations trigger spore release in concentrations? Usually it is some change in their environment. Sudden warming in damp conditions can stimulate spore release in an indoor environment. Using a tumble dryer, ironing clothes, drying wet towels or hanging wet laundry near a strong heat source will stimulate spore production. Bringing damp logs or a plant in from the cold will also produce mould spores. Installing central heating in an old house can bring about sudden concentrations of spores where there were few problems before. A damp spot beneath a dripping radiator valve can induce high levels of mould as the heating comes on. Keeping rooms dry and keeping a steady average temperature can do much to avoid such problems.
Climatic conditions can also stimulate spore release. A warm, humid period of weather in summer will encourage mould production on foliage, crops and plants. If there is then a windy period, the spores can be dispersed and carried even long distances. Some moulds implicated in allergy - Cladosporium, Alternaria, Botrytis Cinerea, StemphylUum - produce spores more readily in a drying wind. They can produce explosive concentrations of spores on hot, dry days in summer.
One allergenic mould - Didymella Exitalis - is very sensitive to moisture levels in the atmosphere. Its sporulation is provoked by dew formation; between June and early September, spores are released at about midnight and reach their peak at 3 a.m. It is also provoked by thunderstorms and reaches a peak some hours after very heavy rainfall in storms.
Another moisture sensitive mould is Sporobolomyces which, like Didymella, reaches its peak on warm summer nights in humid weather. It is at its height usually at about 4 a.m. in late July and August.
Some moulds thrive better in coastal situations, others inland.
Penicil Hum, for instance, does well in coastal sites; Cladosporium, Alternaria and StemphyUium are more prevalent inland.
Warmth and climate changes can thus stimulate spore production in airborne moulds. Disturbing and stirring up the mould’s environment can also produce very high local concentrations in soilborne moulds. Some moulds, such as Mucor and Rhizopus, live in the soil and only become airborne (and thus able to provoke allergic reactions) when they are disturbed. Thus digging a garden, playing in a sandpit and ploughing a field can propel spores into the air.
Other activities, too, can expose high levels of spores. Raking leaves, mowing grass, turning a compost heap, picking fruit, sweeping a yard - all these will throw mould spores into the atmosphere in high concentrations.