JUNE  2004

Don't panic about moulds in the home.   It's not a big deal.

and remember

Moulds in the home are a minor problem in most cases.

I saw a  bit of a television show several nights ago where they were about to do an extreme makeover on a house.   I watched until the commercial!  Apparently there was some mouldy areas in the house and the destructive renovations would have disturbed these and made them a health hazard to all.  So the house was quarantined until it was 'decontaminated' by men in space suits.  Dozens of construction personnel were denied entry and had to wait impatiently, and presumably at great expense, for permission from the 'experts' to enter this hazardous zone.  What extravagant costs these delays caused I have no idea.   But! 

Give me a break!

I think we have put the foxes in charge of the chickens.   We should remember that most of the people who are giving us the 'expert' advice on moulds are the ones who are about to make money if there is a perceived problem ( I wonder how that thought might influence their opinions?).  


Way back in 1955-57, a colleague and I were studying deterioration of corn in storage bins in Iowa.  During this study, we collected hundreds of samples of mouldy corn from numerous bins and in the process inhaled many millions of spores of a variety of fungi, including Penicillium, Aspergillus, and Cladosporium (the big three in homes).  Nearly fifty years later we are still going strong (well, maybe not 'strong' - but were still going!).  

For more details about the corn storage project click here.

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Inside a Butler Bin at a CCC Bin Site Iowa, 1956             Photo: Robert Lichtwardt

We thought it would make an impressive shot if we stirred up the mouldy corn in the upper part of the bin.  My job was to stir up the corn while Bob took the picture with his trusty Exakta.  That's my hand you see there disturbing mouldy corn inside a storage bin (no ventilation, no masks!) and encouraging billions of fungus spores to form a cloud so we could get the definitive shot!  You can see the cloud of fungal spores at the upper right of the shot.   We were breathing that air for maybe twenty minutes.  And you're worried about a little mould on the wall!  

This fortuitous exposure to high concentrations of airborne fungal spores allowed us to formulate the following hypothesis:

'..... it is clear from this experience that normal healthy individuals can be exposed to extremely high concentrations of airborne fungal spores repeatedly with no obvious long term effects on their health. '

alternative hypothesis:

  Bob Lichtwardt and I are special kinds of people.

Note the following:

1. The risks to health in inhaling airborne fungus spores are minor to negligible in the vast majority       of cases.

2. 'Clean country air' can contain tens of thousands of fungus spores per cubic metre.

3. The average person inhales significant numbers of mould spores EVERY DAY.

4. There are probably mould spores in every home in the North America.

5. Valley Fever - caused by windblown spores of Coccidioides immitis in soils of Western NA is a much more serious health hazard than moulds in the home, as are the airborne spores of  Histoplasma capsulatum in Eastern NA and the Mississsippi Valley.

However:  we should also know that there are exceptions to all generalizations.

1. Flooding:

Houses subjected to flooding with water trapped between walls for extended periods can lead to serious mould contamination and appropriate remediation procedures are necessary and often costly.

2. Persistent mould growth on walls, carpets, clothing etc in homes:

This is a very unusual circumstance.  The conditions in the home that led to this proliferation of mould (e.g very high humidity over extended periods with condensation on cold surfaces)should be addressed and when this is solved, the mould problem will disappear. 

3. Mouldy Basements:

If you live in the North where there are basements,  these become very humid in summer and encourage mould growth on organic materials stored in the basement (clothes, leather goods, paper, cardboard etc).  To prevent moulds growing on stuff stored in basements get a dehumidifier and use it in the summer months.  It doesn't have to be set really dry.  60% RH  or slightly lower is OK.   

4.  Mould Allergies:

A small percentage of the population is allergic to mould spores.   If you suspect this to be true get a test to confirm.   If someone in the home has mould allergies then have a central vacuum system installed with the canister outside the home (eg  garage) so that all the materials sucked up are exported out of the home.  Fungus spores will pass through the mesh of most standard vacuum cleaners so vacuuming inside doesn't reduce the spore load and may in fact aggravate the situation by blowing spores all over the house through the back end of the vacuum.  Carpets can be steam cleaned etc using an external, truck-based system external to the home.  i.e. all products of cleaning are exported from the house.

5. Mycophobia:

Airborne fungus spores should be respected but not feared.  There is a current paranoia about Stachybotrys chartarum (the so-called toxic mould).  The dangers from Stachybotrys are way overstated.  

6.  Take what the 'experts' tell you with a grain (spoonful) of salt.

7. For more info on moulds in the home on this website click here and click here