Concerns about mould growing in houses are on the increase, claim mycologists in France. 

Sandrine Roussel at the University Hospital of Besancon and colleagues studied mould present on surfaces and in the air in French houses, with some surprising results.

Mould has been linked to a number of respiratory illnesses, such as asthma and indoor allergies. And is often blamed on poor hygiene and unsuitable usage of housing, for example drying laundry inside.  However, Roussel's study of 500 rooms in 128 houses found that the most important factors were actually the floor the room was located on, lack of effective ventilation systems, types of heating systems used and past water damage.

You may also think the bathroom, where mould is often most visible, would be the worst offender. But mould concentrations in bathroom air were found to be no higher than in bedrooms, kitchens or living rooms. 'Moulds present on walls are not systematically present in the air,' explains Roussel. 'Particular conditions of temperatures, humidity, of circulation of the air are needed so that the spores fall down surfaces and are transported in the air.' 

They also found that 18% of rooms with no visible moulds or smell were highly contaminated. Roussel explains sources of moulds can be hidden behind walls or under carpets. 

The researchers collected data from both questionnaires and air sampling. Roussel believes subjective methods like questionnaires are necessary, but air sampling is also needed to quantify the number and type of spores present.  There are a large variety of mould species which have different effects on health, explains Roussel.

The debate about the necessity to quantify the number and type of spores present in the indoor air is common to numerous countries. Establishing an indoor mould standard is important for health reasons, and would also allow tenants to take proceedings against their landlords. 'Nowadays, no one would agree to live in housing which presents any risks towards lead or carbon monoxide. Tomorrow moulds and other chemical substances will probably follow,' Roussel says.

Sarah Corcoran