The commonest moulds to cause allergies in this country are Aspergillus, Cladosporium, Penicillium and Candida. Moulds prefer warm humid conditions for growth and for releasing their spores. Mould spores can be found in the air between May and October. Where allergy symptoms get worse in late July and carry on to September or October, one ought to think about mould allergy. Some yeasts spore at night so that a damp night can set off large numbers of spores which may persist if the following day is humid or wet. The number of mould spores is affected by the weather so therefore the peak of mould spore concentrations is not necessarily at the same time of year from one year to the next.

Where are mould spores found?
Mould spores are associated with damp houses and dry rot. They are also found outside near rotting vegetable matter such as compost heaps which are being broken down by the moulds. Mould spores are more common in warm weather conditions and on farms, particularly in barns and cowsheds. Seasonal moulds live on leaves of every tree and every blade of grass or cereal. The installation of central heating can cause an outbreak of mould growth because some moulds, such as Aspergillus, and some varieties of Penicillium, grow much faster at higher temperatures. Well treated but badly ventilated rooms full of pot plants, especially if they are standing in a saucer of water, favour mould growth. Clothing and shoes or boots brought in damp and put in fitted cupboards, especially on an outside wall, will soon grow mould.

What can be done? 

• Mould allergies can be diagnosed by skin tests. People who have mould allergies may benefit from improvement to housing conditions, such as damp courses, taking steps to reduce condensation, eg: better ventilation and heating is very important. 
• Mould sensitive people should avoid raking autumn leaves, turning over compost heaps or clearing out greenhouses. 
• They should also avoid walking in woods in damp and foggy weather.