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We inhale about 15 cubic metres of air every day, and you can bet that air contains a good dose of mould spores. We live in a fungal world, and mould in particular grows in at least 30 to 40 per cent of our homes and office buildings.

But when does it become risky to health? And is the much-reviled black mould really the most toxic and dangerous of them all?

A roof in Randwick, Sydney, infested with mould and black mushrooms after tenant Holly reported a drip five weeks ago.Credit: Janie Barrett

It turns out our understanding of this issue was warped by bad science undertaken by the US Centres for Disease Control (CDC) way back in the ’90s.

Fear of toxic black mould still infects public consciousness. But as far as the evidence goes, black mould (the species Stachybotrys chartarum) is no more harmful to human health than any other kind of mould.

The demonisation of Stachybotrys began in the mid-90s with a cluster of 139 babies coughing up blood in eastern Cleveland, Ohio. The infants were diagnosed with pulmonary hemosiderosis, or bleeding lungs. At least 12 died.

A CDC investigation linked the sick babies with homes contaminated by Stachybotrys. Intense media coverage of the CDC’s study ingrained a public paranoia of black mould that would last decades.

But as black mould became the boogeyman, concerned scientists within the CDC assembled a taskforce to scrutinise the study. They uncovered several flaws.

The initial study calculated that for every 10 colony-forming units........

© The Age