Air Quality

Air quality is of fundamental importance to our health. If the air that we breathe in contains particular pollutants it can trigger asthma attacks, heart attacks. Pollutants can be gasses, vapours and particulates. All are capable of penetrating deep into our lungs to some of the most sensitive tissues we have that are exposed to the outside air. Once in our lungs they can irritate, poison and in some cases even penetrate the thin linings of our lungs that are designed to allow gasses to pass through into our bloodstream rather than protect us from toxins. Interested readers can read about that many facetted threat of air pollution at the UK government DEFRA web resources. On the DEFRA website it is possible to access real time data on air pollutants taken at multiple monitoring sites throughout the UK.

Harmful air pollutants are classified into the following categories:

  • Nitrogen Dioxide
  • Sulphur Dioxide
  • Ozone
  • Particles < 2.5µm (PM2.5)
  • Particles < 10µm (PM10)

A committee of medical experts advises the UK government on the health implications of the measured levels of air pollutants (COMEAP).

Air Pollution - Moulds

Moulds such as Aspergillus and Penicillium are frequently found suspended in the air that we breathe throughout the year in the UK. This diagram (taken from the Midlands Asthma & Allergy Research Association website - MAARA) shows that different types of moulds and fungi proliferate at different times of the year in warm temperate areas such as the UK, but all tend to peak in the period from June to August.

Counts taken by MAARA show fungal spores in the air exceeded 50 000 spores per cubic metre of air during this time - mainly Cladosporium, Sporobolomyces  and Basidiospores but also Aspergillus/Penicillium and Alternaria spores. This can far exceed the numbers of pollen grains in the same amount of air.

Analysis of the impact on our health of all these airborne spores is complicated as plant pollens are also plentiful at these times of the year. Hayfever is probably the predominant allergy noted at these times but there is also allergy to all the fungal spores. The symptoms are similar (sore eyes, runny nose, skin rashes) so it is difficult to know if you are suffering from hay (pollen) allergy or allergy to fungi - medical tests are often necessary to distinguish the two.

Fungal spores (2-30 micrometers) tend to be far smaller than pollen grains (10-100 micrometers) and this has an important influence on their pathogenicity. Aspergillus spores can be 2-3 micrometer in diameter which enables them to penetrate deep into our lungs, even as far as individual alveoli. As a consequence pollen tends to cause symptoms in our sinus's and upper airways, some fungal spores can go much deeper into our lower respiratory tract. Fungal spores are also 'seeds' for growth of entire fungal colonies and thus once they manage to get a foothold in our lungs they can grow and be very difficult to eradicate. In contrast pollen grains have a very limited lifespan as they are only intended to grow a short way into a flower before they die!

UK Outside air spore counts

USA Outside air spore counts

Indoor air - Moulds

Some estimates are that we spend 90% of our time indoors so the quality of our indoor air is likely to be very important for our health. We know that outdoor air fundamentally influences indoor air with respect to the numbers of microbes it contains so we should expect that allergy symptoms will continue indoors. Perhaps that is not surprising as other than when we open our windows and doors (which we are likely to do more in the warm summer months when outdoor moulds are at their peak) few homes are completely airtight - if they were we would suffocate overnight! Even very small cracks and gaps seem to be sufficient to allow spores into our homes in large numbers.

However indoors our air can be much less 'fresh' i.e. the amount of air exchange of air between the outside and indoors can be low. In less developed countries people may cook over open or poorly ventilated fires and the smoke released into the home is highly dangerous, causing widespread lung disease.

In the more developed countries of the world there has since the 1970's been a need to conserve energy. In the UK this was achieved by improving the resistance of our homes to losing heat i.e. installing insulation in our walls, roof spaces, improving heating and draughtproofing by installing sealed door and double glazed window units. Open fires have been removed and replaced with gas or electrical fires, chimneys that have been in use for 100 years have been blocked up and often sealed. Homes have become warmer but also much more airtight.

At the same time our living habits have involved us washing more clothing (and often drying indoors), bathing and showering daily rather than weekly. Water consumption in parts of the UK has risen 50% since the 70's.

The net effect of all these changes is that although our homes are warmer, they are more prone to damp as warmer air can hold more moisture which is then released when the air cools e.g. at night when heating is lower. This is particularly a problem in colder weather as walls and windows become colder. Damp is a requirement for mould growth - prevention of damp often requires specialist advice and is a result of both occupant habits and building structure/management.

Health Effects - Moulds

Many people are vulnerable to developing allergies in ways we do not yet fully understand. For the most part they seem to follow prolonged exposure to a particular allergen e.g. breathing in moulds and other substances that can proliferate in damp buildings

Allergic fungal infection

All allergic fungal infections affect the upper or lower respiratory tract, although in a sense all allergies are generalised. There can be an inflammatory component to some skin and mucosal fungal infections, but this is not usually driven predominantly by IgE, eosinophils, mast cells and basophils, the key features of allergic disease.

Many allergies are mild and have a minor affect of health. This section focuses on those that have a major impact on health. Rarely is a person only allergic to one or more fungi; typically affected people have multiple allergies. Some disease states increase the rate of allergies, notably HIV infection and cystic fibrosis but this appears to only be relevant for fungal infection in terms of Aspergillus allergy in cystic fibrosis.

An allergic tendency (or atopy) is often apparent early in life, but can change with age. For example many children with asthma ‘grow out of it’, although some develop it again as they get older. The long term natural history of fungal allergy is not well documented. Some people have allergic fungal infection that comes and goes in severity, usually for unclear reasons. Mucus production and mucosal swelling in the airways, nose and sinuses is the hallmark of fungal allergy.

Most allergic fungal infection probably has an important genetic component. 

The important allergic fungal infections are:

Chronic fungal infection

Evidence is starting to emerge that some people - possible several hundred thousand people in the UK - are vulnerable to deep fungal infections, mostly of the lungs. There are several hundred known cases in the UK but true numbers are probably higher as diagnosis is uncommon and difficult. So speculate that there is a continuum of infection starting with SAFS, then ABPA and we know of a few cases that have progressed to chronic pulmonary aspergillosis.

Certain groups are vulnerable because of pre-existing damage to their lungs e.g. those who have had TB, have Cystic Fibrosis and those with COPD. Genetic research on people with ABPA is starting to reveal consistent genetic features in people who get that chronic infection rendering them slightly less able to quickly fight off a fungal infection, consequently the fungus can start to grow a little and gain a foothold. These patients do not get an invasive infection as their lungs can still fight the infecting mould, but they do generally get a long term incurable, debilitating very slow growing infection.

It might be appropriate to assume that if someone from these vulnerable groups was to be exposed to higher levels of fungal spores in the air, they might run a higher risk of infection compared with the rest of the population. At the moment there is no way to screen for people with many of these genetic differences but that is a primary aim of the research being undertaken.

Some fungi are persistent, defying treatment aimed at cure and leading to long term infection. In most cases, local trauma or damage is a key risk factor, including damage to the cornea of the eye (fungal keratitis) or skin inoculation of a particular fungus such as those causing mycetoma. Prior lung disease is a major risk factor for chronic pulmonary aspergillosis, but it is not known if the same is true for chronic infection of the sinuses.

The inclusion of fungal keratitis and fungus ball of the sinus together in this section is one of convenience, as all patients in this category are not immunocompromised, unlike those with invasive fungal infections.

It is likely that important genetic factors  play a part in determining the persistence of fungal infection leading to chronic disease.

The common chronic and destructive Aspergillus fungal infections are:


Invasive Aspergillosis

This group of infections are important almost exclusively in hospitalised patients who are SEVERELY immunocompromised e.g. those who have had part of their immune system removed for a short time while being treated for cancer, or some who have to be artificially immunocompromised after a transplant (solid organ or haematological). Having little or no ability to fight off infection leaves these patients vulnerable to invasive infection where fungi can grow through infected organs and sometimes spread via the bloodstream.

This can be an extremely difficult infection to treat so every effort is made to avoid infection. The air is the main source of infection both in the operating theatre and in recovery as the main site of infection is the lungs, so indoor air quality is closely monitored in the hospital and cleaned via HEPA grade filtration systems where possible. There have been several research papers that strongly suggest local building works are a factor leading to outbreaks of invasive aspergillosis in some hospitals so local policies have to be put in place to reduce the risk accordingly. Sadly at the moment such measure do not seem to be completely effective and further work has been carried out to try to detect how spores can still infect a few patients e.g. possibly brought in on the clothes of a patient or on the clothes of visitors, in showers or drinking water/food.

Clinician experience, combined with availability of precise rapid diagnostic testing, is the most important factor determining survival from invasive fungal infection. (review: Hidden Killers: Human Fungal Infections, Brown et al 2012)

The most common Aspergillus invasive fungal infections are:

Articles on various aspects of the impact air pollution has on health


Further information


Fumifugium: John Evelyn was a 17th century writer, gardener and diarist. He is best known for his diaries, and was a contemporary of Samuel Pepys (another noted diarist of the time). Evelyn was a prolific writer, and his publications included works on history, religion, forestry, horticulture, architecture, and law.
Fumifugium is the name that Evelyn gave to a 1661 essay on air pollution in London that he sent to King Charles II. Evelyn was enraged by the heavy smog that often fouled the air in his home city. In Fumifugium he aimed to document the impacts of the smog
on people’s health and the environment. He also put forward some solutions to help resolve the problem.

Microbiomes - a rapidly expanding study of the world of microbes that surround us in our environment, and live within us. 

Microbiomes of the Built Environment: A Research Agenda for Indoor Microbiology, Human Health, and Buildings (2017). National Academies of Sciences, Engineering, and Medicine.

Guidelines for indoor air quality in the UK and US

Air Quality control in Healthcare facilities

Control and management of hospital indoor air quality (2006)

National Guidelines for the Prevention of Nosocomial Invasive Aspergillosis During Construction/Renovation Activities (Irish Republic)

Guidelines for Environmental Infection Control in Health Care Facilities (USA)

Health-Care IAQ:Guidance for Infection Control

Links to relevant information sites

Face masks guidelines



Aspergillus and Penicillium Polyphasic identification - This is an interactive key for the identification of Aspergillus and Penicillium species.

Workshops & courses on airborne fungi and other IAQ issues

Information & advice on the diagnosis and the source of damp

European Federation of Allergy and Airways Diseases Patients Associations

Technical University of Denmark (DTU)

Joint Research Centre Institute for Health and Consumer Protection (EU)

International Meetings

IAQ radio Online radio show based in USA. Some good podcasts including: