How Mould Affects Health: A Review of the Science
Updated: May 25
Mould is a common sight in UK homes. Most of us will have experienced mould growth in a house we’ve lived in at some point in our lives. Mould can range in size, shape and colour; from tiny specks on the ceiling of a bathroom to entire walls that seem to have changed colour of their own volition – and everything in between and beyond. It’s no surprise that 51% of renters surveyed by YouGov, said they’ve experienced a damp and mould problem in one or more of their rentals. The UK climate is extremely conducive to mould growth. This is because mould is exclusively caused by excess moisture or damp.
There are, broadly, three types of damp: rising damp, penetrating damp and condensation. Condensation is easily the biggest cause of mould in the UK, no doubt because of the ubiquity with which it afflicts our homes. Condensation forms when warm air collides with cold surfaces, or when there’s too much humidity in your home. So, unless you’ve developed a thermally impervious layer of skin, or are warmed by the thought of saving money on the heating bill, there’s a good chance you’ll be cranking the central heating up for around a third of the year. Warm air, meet cold surfaces. Then, there’s the fact that condensation is exacerbated by moisture-producing behaviours like cooking, showering and drying clothes on radiators. All are variables that, together, create the perfect storm of conditions for mould growth. So, you’ve found some mould in your home. Let's review whether or not it poses a risk to your health.
Is Mould Toxic to Humans?
Want the short answer or the long answer? The short answer is yes (sorry, spoiler alert.) The long answer goes like this: The World Health Organisation (hereafter referred to as the WHO) undertook a pretty comprehensive and robust 248-page study in 2009, entitled ‘WHO guidelines for indoor air quality: dampness and mould’. They found the following:
“Microbial growth may result in greater numbers of spores, cell fragments, allergens, mycotoxins, endotoxins, β-glucans and volatile organic compounds in indoor air. The causative agents of adverse health effects have not been identified conclusively, but an excess level of any of these agents in the indoor environment is a potential health hazard.” WHO, 2009
In essence, this means that mould, which is a microbe, contributes to poor air quality in your home. More specifically, mould releases ‘agents’ into your airspace which, when inhaled or touched, can cause or exacerbate ill health. However, they have stopped short of pinning the blame for any adverse health effects on any single agent. Mould is known to produce most if not all of the agents outlined by the WHO, including mycotoxins, VOCs, mVOCs, β-Glucans and allergens.
The WHO present their findings in two parts. An examination of the epidemiological evidence and an examination of the clinical evidence. Epidemiological studies are concerned with data trends displayed by large groups of people, while clinical studies are concerned with the individual. There are, therefore, much higher thresholds applied to hypothesis testing with epidemiological studies as they evidence widespread prevalence. The clinical data can often constitute the first instance of something appearing on the collective radar. It should, therefore, not be disregarded, particularly as it pertains to an area that is in its relative infancy.
The Epidemiological Evidence
The WHO state there is epidemiological evidence that links mould to the following illnesses and symptoms:
Exacerbation of asthma
Upper respiratory tract (nasal and throat) symptoms
Allergic fungal sinusitis
The Clinical Evidence
There is a huge body of scientific data which goes a lot further than the epidemiological evidence. We’re not just talking tabloid clickbait articles: ‘The Mould in my Bathroom Made Me Worship the Devil’. We’re talking peer-reviewed, controlled, rigorous studies undertaken by prominent academics and scientists working at Universities around the world. Dr Joseph Pizzorno, Chief Editor of Integrative Medicine: A Clinician’s Journal, does his best to summarise and categorise the data from the circa 10,000 peer-reviewed studies into the health effects of mould. He states that though mould toxicity can and does affect all systems of the body, it affects three most often. The respiratory system is most affected, followed by the neurological and immunological systems.
We’ll take a look at some of the clinical evidence presented by the WHO, Dr Pizzorno and other scientists. It’s important to state at the outset; some of these studies merely point out possible causal links between mould and illness and disease. They do not, nor do we, state that the following illnesses are directly and undeniably caused by mould. They simply present a potentially significant link that requires further investigation.
A lot of the respiratory illnesses and symptoms caused by mould are already reflected in the WHO epidemiological list above. Dr Pizzorno has also assembled a list of respiratory diseases and symptoms typically caused by mould below:
Asthma. It’s worth drawing particular attention to asthma as mould exposure is deemed to be a major factor in its development, particularly amongst adults. One study found that of a cohort of 1,300 office workers, 67% of adult-onset asthma sufferers developed the disease after working in a water-damaged office building.
Allergic Alveolitis or Hypersensitivity Pneumonitis. It’s considered primarily induced by mould exposure. Its symptoms include cough, shortness of breath and sometimes fever and joint pains.
Fatigue, headache, brain fog. A 1996 study showed an association between mould exposure and impaired cognitive functions. Some mycotoxins, products of Fusarium, Stachybotrys, Aspergillus and Penicillium – common household mould strains, have proven to be neurotoxic in vitro and in vivo. In other words, they are harmful to the brain and can cause adverse mental health effects.
Decreased balance, increased colour discrimination errors, decreased visual field, reduced grip strength, cognitive and memory performance issues. A 2008 study found that individuals that had been exposed to mould and its various agents were suffering from a wide range of neurological issues.
Significant loss of visual contrast sensitivity. This 2003 study demonstrated a link between mould in a water-damaged office-block and a significant neuro dysfunction affecting visual perception.
Neurological cell damage. A 2010 study found that trichothecene mycotoxins can cause neural damage by way of inflammation and oxidative stress. Neurological cell damage can be varied in the devastating symptoms it causes, depending on the location of the damage.
Mould infection amongst the immune-suppressed. Individuals who are immune-compromised (e.g. to treat cancer or infection with human immunodeficiency virus) can become infected, usually by the mould strains Aspergillus or Fusarium, which can pile an array of complications on top of already overwhelming health challenges.
Immunosuppression. A study in animals has demonstrated the immunosuppressive effects of mycotoxins. Some mycotoxins impair immune responses, meaning some infections are far more severe than otherwise – particularly immune responses to respiratory virus infections.
Inflammation. Inflammation is an immune-system response and is designed to defend you against harmful agents such as bacteria and viruses. However, it can damage your arteries, organs and joints over time and eventually cause chronic diseases such as heart disease, diabetes, cancer, Alzheimer’s and obesity. A 2015 study found that chronic mould exposure causes multiple inflammatory measures up to a 1000-fold increase in these inflammatory mediators.
Multiple Sclerosis. One study demonstrated a link between MS and mould. The incidence of MS rises the further one gets from the equator. This study theorised that the rise in the incidence of MS coincides with a rise in mould (damper climates) and a fall in Vitamin D (less sunlight). They argue that the lack of Vitamin D (necessary for immune system regulation) and the immune-suppressive nature of some mycotoxins (particularly gliotoxin) can combine to cause MS.
Chronic Fatigue Syndrome. A 2013 study found that 93% of patients suffering from CFS also had one mycotoxin present in a urine test and 30% had two present.
Increased risk of allergy to other allergens. A study found that exposure to mould increases the risk of allergy to other allergens such as pollen and dust mites.
As discussed above, there is evidence to suggest that mould exposure can adversely impact all biological systems within the human body. Here we take a look at just a few amongst the many links highlighted by scientific studies.
Cancer. It would be both irresponsible and evidentially unfounded to claim that mould exposure is a direct cause of cancer. But it is important to acknowledge the below from the WHO's 2009 report:
“Some of the microbial toxins produced by bacteria and fungi are known to be genotoxic and carcinogenic (IARC, 1993), but the relevance of these findings to exposure by inhalation in damp buildings is not known.” WHO, 2009
It appears that some mycotoxins may indeed be carcinogenic, but there is, as yet, no demonstration of a causal link between the inhalation of the mycotoxin and the onset of cancer.
Toxic Agents of Mould
It sounds like an evil group of assassins from a comic book, and admittedly they are indiscriminately destructive. Here we take a look at the agents with which household mould pollutes your airspace.
VOCs are produced by a chemical reaction that occurs as mould consumes its ‘food’. ‘What does mould like to eat?’ you may be asking. Well, because it’s semi-relevant and semi-interesting, we’ll take a brief look. The answer is: it’s a pretty undiscerning customer. Mould eats any organic material (anything with a carbon atom present). Mould goes crazy for cellulose in particular, washed down with a nice glass of Bordeaux (we imagine). Cellulose is found in common building materials like wallpaper, wood and natural fibres. It contains sugar and starch, which is really what the mould is after. And who can blame it? Mould can, however, grow on any surface. Most surfaces will be coated in something called ‘biofilm’, which mould will also munch away at. In plainer terms, biofilm is a slightly more ‘sciencey’ way of describing the invisible layer of detritus on all household surfaces comprised of dead skin cells, oils, food waste, insect droppings and other such mouth-watering fare.
The VOCs produced by mould, or mVOCs (methane VOCs), enter the body through the lungs and skin.
“mVOCs increase inflammation biomarkers… and they cause headache, nausea, and mucosal irritation.” Dr Joseph Pizzorno
Dr Pizzorno explains that much research is currently being undertaken regarding the health effects of mVOCs, but aside from the aforementioned illnesses, inflammation is a worrying sign indeed, given the chronic illnesses it can cause if left unaddressed.
The clue with this one is in the name. ‘Myco’ meaning relating to fungi, and ‘toxin’ meaning a poison. It might, therefore, be relatively safe to infer the existence of a prevailing school of thought that deems mycotoxins, or ‘mould poison’, harmful. Mycotoxins are the most well-researched agent with regard to their effects on human health.
"Many studies in vitro and in experimental animals have demonstrated the toxic potential of a variety of mycotoxins" WHO, 2009
But what are they? Simply put, mycotoxins are the chemical excretions of mould. They can be as varied in their chemical make-up as the tens of thousands of strains of mould and fungi that produce them. However, there are some strains of mould that are more commonly found in the home.
12 most common types of household mould:
The WHO state that there are just a few studies that have examined the health effects of β-Glucans through the exposure of humans to mould or glucans. After all, one would imagine volunteers hard to come by. They do reference a series of studies that were carried out by Rylander and colleagues in Sweden. They found, that in buildings where there were high concentrations of β-glucans, the following symptoms and illnesses were manifest:
“symptoms such as dry cough, nasal and throat irritation, hoarseness and tiredness and headache were found to be more prevalent. A few cases have also been published in which inhabitants of houses with signs of mould and with airborne glucan levels > 100 ng/m3 were severely afflicted with asthma-like symptoms until they moved.” WHO
It is important to note, however, that they also deem these studies to be insufficient to conclude that there is a causal relationship with glucan, as it may be a marker of exposure to another agent.
Mould is dangerous. Of that, there is no debate. It is the severity of the danger it poses which is still very much the subject of intense debate within the scientific and medical communities. To add complexity to an already complex debate, one's susceptibility to mould toxicity varies drastically based on genetic predisposition and allergy, not to mention the immense biodiversity of mould and the array of chemical agents it produces. If you inhale mycotoxins over a short time horizon then there's a chance you'll experience congestion and perhaps an irritated throat and eyes. It's the longer time horizons that should be of most concern. Mycotoxins, mVOCs and β-glucans simultaneously suppress the immune system and cause inflammation, which, if left over a long period of time, could have catastrophic effects on your health.
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WHO guidelines for indoor air quality: dampness and mould. WHO Regional Office for Europe. Link
Mold Basics. Kathleen Parrott, Ph.D., Professor of Housing, Virginia Tech. Link
Is Mold Toxicity Really a Problem for Our Patients? Part I—Respiratory Conditions. Joseph Pizzorno, ND, Editor in Chief. Link
Is Mold Toxicity Really a Problem for Our Patients? Part 2—Nonrespiratory Conditions. Joseph Pizzorno, ND, Editor in Chief and Ann Shippy, MD. Link
YouGov: Renters. https://static.safeguardeurope.com/downloads/reports/yougov/yougov-home-fitness-for-human-habitation-01-04-2019.pdf
Respiratory morbidity in office workers in a water-damaged building. Jean M Cox-Ganser 1, Sandra K White, Rebecca Jones, Ken Hilsbos, Eileen Storey, Paul L Enright, Carol Y Rao, Kathleen Kreiss. Link
Health and immunology study following exposure to toxigenic fungi (Stachybotrys chartarum) in a water-damaged office environment. E Johanning 1, R Biagini, D Hull, P Morey, B Jarvis, P Landsbergis. Link
Acute effects of 1-octen-3-ol, a microbial volatile organic compound (MVOC)--an experimental study. Robert Wålinder 1, Lena Ernstgård, Dan Norbäck, Gunilla Wieslander, Gunnar Johanson. Link
Effects of Toxic Exposure to Molds and Mycotoxins in Building-Related Illnesses. William Rea. Link
Building-associated neurological damage modeled in human cells: a mechanism of neurotoxic effects by exposure to mycotoxins in the indoor environment. Enusha Karunasena 1, Michael D Larrañaga, Jan S Simoni, David R Douglas, David C Straus. Link
T-2 toxin impairs murine immune response to respiratory reovirus and exacerbates viral bronchiolitis. Maoxiang Li 1, Jack R Harkema, Zahidul Islam, Chistopher F Cuff, James J Pestka. Link
Environmental mold and mycotoxin exposures elicit specific cytokine and chemokine responses. Jamie H Rosenblum Lichtenstein 1, Yi-Hsiang Hsu 2, Igor M Gavin 3, Thomas C Donaghey 4, Ramon M Molina 4, Khristy J Thompson 4, Chih-Lin Chi 5, Bruce S Gillis 6, Joseph D Brain 4. Link
Fungal toxins and multiple sclerosis: a compelling connection. Catherine B Purzycki 1, Daniel H Shain. Link
Detection of mycotoxins in patients with chronic fatigue syndrome. Joseph H Brewer 1, Jack D Thrasher, David C Straus, Roberta A Madison, Dennis Hooper. Link
Fungal secondary metabolites as harmful indoor air contaminants: 10 years on. J David Miller 1, David R McMullin. Link