Aspergillus, in common with many other moulds, can produce highly toxic chemicals known as mycotoxins. Some of these are useful and well known e.g. alcohol & penicillin. Others are gaining recognition for less useful purposes as they contaminate food and animal feeds and make it unusable or uneconomic forcing the value of a crop downwards, something that is particularly painful in the developing countries.

There is a fair amount of research available on the effect of mycotoxins on the productivity of farmed animals, but very little on the effect of mycotoxins on humans.

Much is currently being made of the possible health effects of mycotoxins produced by fungi growing in damp buildings. This is a source of great debate and more than one vested interest has given its opinion. The debate gets very technical so in a few simple points:

• Toxins are present in an airborne form in at least some damp buildings, or buildings with poorly maintained air conditioning
• The AMOUNT of toxins ingested by breathing will usually be too low to cause an acute (immediate) toxic effect on health, though these figures are based on toxicity in animals other than humans. Some humans may be more sensitive than animals or each other.
• We do not fully understand all of the potential sources of mycotoxins
• Repeated exposure to low doses of mycotoxins has been shown to affect health in animals
• Different mycotoxins can work together to cause health problems in animals such that neither has an effect on its own, but together they can. Mycotoxins may well be present in combination in damp buildings - this is a risk whose extent isn't yet known

All in all there is more than adequate evidence that shows damp buildings are a risk to health. Whether mycotoxins contribute to those health problems is debated, though the debate is strongly biased both ways. We do not know enough to say that they don't have a major effect on health, and we do know that in conditions that would promote their production there are clear health problems, and that when the houses are cleaned up and well ventilated those health problems improve.