Mould Heath Concerns

Health effects of moulds: State of knowledge

These are the results of ‘peer reviewed’ scientific/medical papers:
“In July of 2009, the World Health Organization (WHO) published its position paper on indoor moulds and Indoor Air Quality. Contrary to what many people in the mould remediation business want to believe, the WHO guidelines reinforced the findings of the 2004 Institute of Medicine mould study group. That is, after reviewing the global scientific and medical literature, the IOM could not find sufficient evidence to support the argument that the normal presence of mould in residences and workplaces caused any adverse health effects.”
These findings are consistent with other notable organizations, such as the “Health Alert” published by University Health Publishing and John Hopkins Medicine who state:
“Just because a particular mold can produce toxins doesn’t mean it will. Even if the mold is producing toxins, a person must breathe in a sufficient dose to be affected. It is highly unlikely that you could inhale enough mold in your home or office to receive a toxic dose.”
Paper can be found at

by C.P.Connell, Forensic Industrial Hygienist (2009)
mould on fireplace
Mould growing on the inside of a fireplace.
The wall is a single brick thick, causing realtive humidity to rise above 85%RH.


There are 4 species of moulds that are considered to be a so-called ‘toxic mould’

  1. Stachybotrys – a black/brown mould that grows on cellulose substrates, e.g., paper, cardboard; slimy: requires very wet/damp substrate such as following flooding
  2. Penicillium
  3. Aspergillus 
  4. Fusarium

“Current scientific evidence does not support the proposition that human health has been adversely affected by inhaled mycotoxins in the home, school, or office environment.”
American College of Occupational and Environmental Medicine Council on Scientific Affairs. Evidence-Based Statement. “Adverse Human Health Effects Associated with Molds in the Indoor Environment.”

JOEM 2003: 470-478

In the words of the PCA (Property Care Association)

“The term ‘toxic mould’ was given by the media – it is not a scientific description!!”

German Mould Guide (2002) reported: (1)

Very rare and almost exclusively occurring in the workplace is extrinsic allergic alveolitis (hypersensitivity pneumonitis) which is generally produced by repeated exposure to very high concentrations of spores (106-108/m3); which cannot be expected to occur (residential) indoors.

Occupational exposures:

  1. Lumber Mills: 106-108/m3 (2) 
  2. Silos 106 /m3 (and greater) (2) 
  3. British Farms 106 /m3 (4)
  4. Barns: 104/m3 (and greater) (2) 
  5. Grain harvesting 107/m3 (2)
  6. Potting sheds (3)7,500 spores/m3 S. chartarum
mould by window
Mould in a bedroom, by the bedhead. No ventilation.

The guidelines [NY City Dept of Health] continue

Finally, Both the WHO and the Institute of Medicine both concluded that there was an association between damp living spaces and some adverse health effects. But no one has been able to conclusively demonstrate that the association is exclusively due to the presence of mould, and both organisations note that dust mites, bacteria, termites, protozoans, endotoxins, volatile organic compounds, formaldehyde, pesticides, viral survival and generally poor ventilation are similarly associated with damp, and these factors are considered to be part of the aetiological backdrop. As such, the stress is placed on correcting damp.

Based on peer-reviewed literature the fundamental problem is one of a long term damp environment.
This gives rise to moulds, dust mites, bacteria, virus’, volatile organic compounds, etc these are ALL associated with a damp environment!

So while ‘toxic moulds’ are not a total myth they are certainly nowhere near as devastating as the media would have us believe. A majority of reported allergies are to dust mites. Penicillin is known to cause allergic reactions. However, it is unlikely that toxins become airborne in sufficient quantities to cause allergies in a home.

The above data with the kind permission of C. Connell, Forensic Applications Inc

  1. Connell’s translation from the original German Guide The prevention, investigation, evaluation and rehabilitation of Mould growth indoors Created by the Indoor Air Hygiene Commission of the Federal Environmental Agency
  2. Ron Gots, MD, PhD
  3. Connell’s translation from the original German; Dill and Trautmann “Massenentwicklung von Stachybotrys chartarum auf kompostierbaren Pflantztöpfen aus Altpapier” Mycoses 40 (Suppl 1) p. 110-114, (1997)
  4. Swan JRM, Blainey D, Crook B. (2007). The HSE Grain Dust Study – workers exposure to grain dust contaminants, immunological and clinical response. RR540. HSE.

Understanding Excess Humidity

Relative humidity is the water-vapour content of the air relative to air’s capacity to hold water vapour, expressed as a percentage (%RH). 

  • 100%RH is reached when air is saturated with water vapour.
  • The capacity for air to hold water vapour varies with temperature.
  • Air at 10˚C can hold roughly half the water vapour of air at 20˚C.
  • So, when 60%RH air at 20˚C meets a cold surface at 10˚C, roughly 10% of its vapour will condense on the cold surface. 
  • Condensation starts when the temperature drops below the dew point.
  • Evaporation starts when the temperature is above the dew point.
  • Typical dew points are 12˚C in winter & 19˚C in summer.

Condensation is not a health issue, but the risk is rot which can cause expensive structural damage. There are no proven examples of mould causing health issues, but dust mites which grow in humid conditions, can cause allergies. Healthy tenants tend to be better tenants.

There is a dynamic equilibrium in every property between Vapour inand Vapour out. If vapour is added, such as by boiling water, it needs to be extracted. Otherwise, water vapour will condense into walls and fabric. Walls lose heat rapidly and mould may grow.

W.H.O. (World Health Organisation) guidelines for indoor air quality 

 “Management of moisture requires proper control of temperature and ventilation to avoid excess humidity, condensation on surfaces and excess moisture in materials. Ventilation should be distributed effectively throughout spaces, and stagnant air zones should be avoided. 

Building owners are responsible for providing a healthy workplace or living environment that is free of excess moisture and mould, by ensuring proper building construction and maintenance. 

The occupants are responsible for managing the use of water, heating, ventilation and appliances in a manner that does not lead to dampness and mould growth.” 

The tenant has a duty to use the facilities provided by the landlord, informing the landlord as soon as a facility is in disrepair. Tenants have the responsibility to ventilate and heat a property, clean mould away and wipe down condensation. 

A typical house contains 30 – 40 litres of atmospheric water. Each day, each occupant adds about 1.5 litres each day. If it isn’t vented out, it will condense into walls and cause mould. 

  • 0.8 litre in respiration, (about 0.25 litres at night) + water for plants and pets
  • 0.5 litre per shower,
  • 0.5 litre for washing, 
  • 0.25 litre cooking,

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