Skip to content

News & opinion

12 DEC 2019

Spore law: How to control mould and prevent hazards to health

Moulds are a ubiquitous part of our ecosystem. Their spores and fragments are always present to a greater or lesser extent in our houses, workplaces and public buildings, whether these structures are modern or historic. It is important to accept that there is always a little mould everywhere – in the air we breathe and on many building surfaces and contents.

But when mould spores land on places where there is excessive moisture, such as properties suffering from condensation, rising damp, penetrating dampness or leaks, these spores will grow. Many building materials provide nutrients that encourage such growth.

Impact and identification

Although the word ‘mould’ is widely used as a collective term for spore-producing hyphomycetes fungi, the phrase ‘toxic mould’ is not scientifically accurate, as moulds are not themselves toxic or poisonous. Rather, they are toxigenic, meaning they can produce toxins – specifically mycotoxins.

The scientific community does not therefore refer to toxic mould, as the toxic effects of airborne exposure to mould are not well documented. Likewise, medical doctors do not recognise the term, instead focusing on the well-established connection between the allergenic effects of mould and the human body.

Mould growing in a home
Although all properties have some mould, very high levels can start to affect people's health

Moulds can have multiple health effects, such as respiratory distress, allergy to spores, or fungal infection, particularly in susceptible individuals. Some people are sensitive to mould spores, and exposure can lead to symptoms such as stuffy nose, wheezing, and red or itchy eyes or skin.

Those who are allergic to moulds or are asthmatic may have more intense reactions, and mould or dampness may even lead to development of asthma in some individuals. Likewise, people with weak or compromised immune systems, chronic respiratory disease or underlying lung conditions are more likely to get infections from mould.

Mould is a living organism and will continue to proliferate in the indoor environment as long the conditions favourable to it remain. It is therefore essential to seek building mycology advice as soon as practically possible. This is the discipline that deals with fungi in and around buildings, especially the kinds that have a direct or indirect effect on the fabric, its materials and structures, environments and occupants.

The scientific community does not refer to toxic mould, as the toxic effects of airborne exposure to mould are not well documented

When dealing with any indoor mould contamination, a common-sense approach should be taken. The process will involve the following:

  • Monitoring the building structure and external environment
  • Carrying out a mycological assessment of the indoor environment
  • Assessing the medical history of the occupants, including asking the occupants whether they suffer from asthma or are sensitive to mould
  • Ensuring your health and safety, with the use of personal protective equipment (PPE) for instance
  • Regular maintenance and monitoring measures to prevent recurrence of mould growth in the home.

To explain each of these in more detail, it is standard practice – and in my opinion essential – for any building mycologist to measure moulds immediately outside the property to determine the levels, types, composition and species, as this will enable comparisons with the indoor environment.

Most often, mould infestation indoors is not readily visible to the naked eye, but is detected by monitoring, sampling, culturing and microscopic identification of hyphae, or fungal filaments, and the conidiophores that some hyphae produce, as well as conidia and other spores. Methods used in detection include airborne, contact and particulate sampling analysis.

The most frequently observed effects among the mould-associated health disorders include irritation of the mucous membrane in the eyes and the respiratory tract as well as allergic reactions. In 2004, the Institute of Medicine found suggestive evidence linking indoor mould exposure and respiratory illness in otherwise healthy children, and in 2009, the World Health Organization (WHO) issued the WHO guidelines for indoor air quality: dampness and mould (

Recommended reading:

Row of red brick terraced houses
Often, mould indoors isn't even visible

Stachybotrys chartarum – often referred to as toxic black mould, even though many other species are black and produce mycotoxins – has been implicated in illnesses suffered by those living in damp houses, and can grow on wallpaper and plasterboard when these have become extremely wet.

Reports of idiopathic pulmonary haemorrhage in very young children living in water-damaged homes in Cleveland, Ohio have put the spotlight on this group of moulds. This, along with several multi-million-dollar lawsuits, this has seen mould getting considerable attention in the US media. Meanwhile, UK insurance companies that cover professional indemnity for the building industry recently introduced a clause excluding mould and asbestos work.

Although in most cases mould contamination can be removed from hard surfaces by thorough cleaning with commercial products, soap and water, or a weak bleach solution, using adequate PPE including non-porous gloves and protective eyewear, severely contaminated porous or absorbent materials such as ceiling tiles, gyproc plasterboard and carpets may well require disposal.

 It is important to use a high-efficiency particulate air filter to vacuum-clean and remediate mould contamination from the building fabric, structure and contents. Failing to clean and remediate thoroughly could cause the occupants exposed to it to suffer an allergic reaction, even to dead mould.

The building fabric, structure and contents should also be dried to acceptable levels, with timber moisture content below 16 per cent, and ambient relative humidity indoors maintained within acceptable limits, that is, below 70 per cent. Failing to do so may lead to the recurrence of mould growth, proliferation and contamination. PAS 64: 2013 Mitigation and recovery of water damaged buildings: Code of practice, developed in collaboration with BSI, offers more advice.

Cleaning a brown wooden floor
Carefully cleaningmould is incredibly important

Investigation and remediation

After a pipe burst on the seventh floor, a multi-storey block of flats suffered from water damage, damp, condensation and moisture throughout, including ingress into cavities and voids (see photos[, position]). With inadequate ventilation and high levels of humidity, this enabled the growth of a variety of moulds, bacteria and other biological agents.

Residents reported a range of issues, including the mouldy odour associated with microbial volatile organic compounds. WHO guidelines for protecting public health stress the need to prevent or minimise persistent dampness and microbial growth on interior surfaces and building structures.

After an initial survey of the damage, I recommended the appointment of a strip-out contractor. Moisture-saturated materials were removed and the building fabric dried to acceptable levels, which were independently monitored. Mould levels and relative humidity levels in the floor slab were checked, and where the latter were at or below 75 per cent the slab was certified as dry.

Tests were also undertaken for airborne moulds and particulate matter, surface moulds and mould in cavities and voids, and a remediation company was then employed to treat the property as my report specified. Following the treatment, all the rooms in various flats were tested to check that the contamination was below the levels recommended in the WHO report Indoor air quality: biological contaminants.

Recommended reading: