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Mould Facts

Updated on
January 18, 2024

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Mould: A Factfile

  • There are approximately 100,000 species of mould
  • There are numerous strains of 'black mould'
  • Typically, the black mould referred to by homeowners is Stachybotrys chartarum
  • Mould can change colour depending on the "food" it consumes
  • Mould is in the kingdom of fungi (alongside mildew, rot, toadstools etc)
  • Mould spores typically range between 2µm to 20µm (microns) in size
  • For reference, there are 1,000µm in a millimetre
  • Single mould spores are invisible to the human eye
  • Mould spore and hyphal fragments can be as small as 0.3µm
  • A colony consists of a mass of hyphae which collectively form a mycelium
  • 1 square centimetre of penicillium growth can support up to 80 million mould spores
  • When you see mould growing on a wall, ceiling or other surfaces, you're looking at a mould colony
  • A mould spore is, essentially, a mould seed
  • Mould spores are everywhere. They are present in outdoor air and attach themselves to clothing, hair, footwear and even pet fur. They can blow through windows, doors, vents and chimneys
  • Mould spore levels will vary from location to location (e.g. if you live near woods or fields) and at different times of day and different times of the year
  • Humans can tolerate the levels of mould typically found in outdoor air
  • The level of mould in outdoor air is typically referred to as 'the normal ecological background level'
  • Mould thrives in high humidity or damp conditions. It struggles to grow in dry conditions
  • Moisture levels in the air and in surfaces may not be as self-evident as you may think
  • If your home is suffering from a mould problem, there is some form of damp problem also
  • There are many causes of damp in a building and there are different types of damp, categorised by their causes
  • When mould is allowed to grow in a building, given its enclosed structure, it creates unnaturally high concentrations of mould spores in the air and on surfaces
  • Given their size, mould spores can defy gravity and float through the air indefinitely - a phenomenon known as Brownian Motion
  • Disturbing mould itself or even the air around it will send mould spores into the air
  • Attempting to clean or wipe the mould away will cause mould spores to enter the airspace
  • Typically, a DIY mould clean will spread spores and hyphal fragments as the mould. act in self-preservation - even if the bulk of the colony is killed or physically moved.
  • The plethora of airborne spores will seek damp surfaces on which to land, and mould will begin to grow once more
  • Mould, its spores and the toxic agents it produces (mycotoxins, mVOCs, b-glucans and hyphal fragments), are hazardous to human health
  • Mould spores, even those that have been damaged by chemical cleaning products and cannot reproduce, are still respirable and can cause negative health effects
  • Mould spores are allergenic and some may be toxigenic
  • Mould colonies compete with one another for food sources (as most species on the planet)
  • Rival mould colonies produce gases as both a defence and attack mechanism
  • Some gases produced by mould are toxic to humans
  • Cleaning mould with over the counter products like bleach triggers the same survival mechanism
  • Human tolerance to the toxigenic properties of mould differs from person to person, based on the uniqueness of our individual immune systems
  • It's expected that scientists will discover and name an estimated 200,000 to 1.5 million more species of mould
  • The average homeowner or tenant will have no idea of when mould has been removed and cleaned due to the microscopic size of the spores. They'll typically make it much worse and expose themselves, colleagues and occupants to elevated levels of spore, hyphal fragment and toxin inhalation
  • This means doing a poor job of cleaning, destroying and removing mould can be worse than leaving it
  • Control of Substances Hazardous to Health (COSHH) Regulations 2002 (revised 2013) refer to fungi as asthmagens. (COSHH Regulations fall under the Health and Safety at Work Act 1974.)
  • The UK government classify mould as a Category 1 Health Hazard - the same as asbestos (HHSRS)
  • World Health Organisation guidelines for indoor air quality and dampness describe mould as a health hazard
  • National Health Service publications list mould as a health hazard.
  • There is also evidence some of the toxic agents produced by mould are mutagenic (affecting unborn babies), carcinogenic (cancer-causing), estrogenic (affecting human reproductive systems)
  • It's commonly accepted that some mould strains are pathogenic, toxigenic or allergenic. All mould is asthmagenic
  • Mould has the capacity to make people sick. It is one of the contributing factors to what is known as SBS “Sick Building Syndrome” or BRI “Building Related Illness”
  • Remember, the Health and Safety at Work Act 1974 and its regulations apply to all work carried out in a house as well as any commercial building. This applies to volunteers working for charities as well as tradesmen and contractors
  • NHS documents claim that if you are prepared to remove mould growth yourself in your own home, you should not do so when the growth exceeds 1m² and that you should call in a professional service
  • A professional mould remediator must be competent (i.e. trained in the task they are performing) and that means understanding mould is a hazardous material
  • A professional mould remediator must carry out an appropriate risk assessment and take appropriate control measures
  • A professional, trained and competent remediator will, amongst other things, need to consider: whether sampling, testing or speciation is required and how much is required, what containment measures are required and how to set it up, what air filtration and air exchange is required, what level of Personal Protective Equipment (PPE) is required, what level of clearance testing is required and whether an independent 3rd party environmental hygienist should do it