Healthy Indoors


Invisible, but essential: the microbiome

We talk a great deal on the Healthy Indoors website about things you can see, feel, touch and measure and how such factors affect our health. But there is another dimension, one that perhaps has an even greater impact on our health: the microbiome.

Invisible, but essential: the microbiome

It is a sphere that is to the human eye invisible, yet diverse, vigorous, and essential to our health. The built environment alone encompasses trillions of microbes, including bacteria, fungi and viruses. The extent of the microbial diversity in the natural world is infinite.

The term ‘microbiome’ often refers to the family of microbes whose home is our bodies. Then there are the microbiomes of built environments, which receive less attention. These microorganisms are vital to our immune systems, metabolism, emotions and more, helping to synthesize vitamins, hormones and other chemicals and keeping us healthy, even alive! These beneficial organisms have developed with humankind since our beginning, accompanying us in our caves, huts and now our modern buildings.

More species of bacteria have been found in homes than there are species of birds and mammals on Earth, according to Rob Dunn, a Professor of Applied Ecology at North Carolina State University. In 2015, researchers found that indoor air contains nearly equal concentrations of bacteria and viruses.

Unfortunately, though, human microbiomes have changed and decreased significantly due to changes in our diets, use and overuse of antibiotics and disinfectants and less frequent interaction with animals and nature. The same is true of our inhabited spaces, where the multitude of microbes is increasingly absent, resulting in a greater incidence of infectious disease and allergies. Because buildings, like humans, are only as healthy as their microbiomes.

Plants make indoor spaces healthier by adding valuable natural microbes.

Contrary to preconceived notions, not all germs are bad!

Growing up and living in modern Western society, most of us have an ingrained notion that germs are bad. Germs mean sickness. Everywhere, you see antibacterial soaps, sprays, cloths, etc. Some of us still have the image of workers clad in medical protective isolation clothing going through streets spraying disinfectant to kill the coronavirus. Have you ever wondered if their actions might also destroy good microbes or the microbial balance? 

Did you know that most microbes are beneficial and necessary to life? In fact, left alone, these organisms tend to regulate themselves, keeping the ‘bad guys’ in check, thus maintaining equilibrium. Organic gardeners know this and do all in their power to encourage microbial diversity in their soil, rather than trying to eradicate the bad microbes.

 Science has determined that greater microbial diversity is desirable. So how does that apply to indoor environments and how can we encourage greater diversity?

Our knowledge in this area is in its infancy: it wasn’t until 15 years ago, that a few scientists began looking into indoor microbes, no doubt, because of outbreaks of legionella bacteria, the cause of Legionnaires’ disease, and black mold. Architects and designers were even slower to turn their attention to the subject. The pandemic, however, may be changing how we view things. Once we accept the fact that greater microbial diversity is desirable, it’s time to take a closer look at what we do and our surroundings.

Dryness and unnatural materials cause microbial stress

In today’s built environment, the spaces where we spend over 90% of our time, beneficial microbes struggle to gain the upper hand.

Until recently, we have directed the bulk of our efforts toward improving the energy-efficiency of our built environs, that is, making them tighter and tighter. This resulted in a rise in average indoor temperatures and a decrease of relative humidity – it’s physics! These efforts also have brought one high-tech material after another into our buildings, as we increasingly employ synthetic materials and manufactured materials such as steel, glass and plastics in the fit-outs and construction. Unlike natural building materials, which include tiling, plaster, clay or wood, these industrial products are usually smooth-surfaced, non-porous materials, that are incapable of absorbing, retaining and releasing moisture or nutrients.

As such, these materials constitute a hostile environment for the beneficial microbes we have come to depend on from the dawn of humankind. If this trend continues, we will, at some time, have effectively tipped the scales in favor of a microbiome that does not match our evolutionary development. At that point, we are defenseless. Many of these pathogenic microorganisms are developing resistance to our antibiotics, disinfectants, etc. Indeed, many scientists are sounding the alarm, saying the covid pandemic is just the beginning. So now is the time to act, see the whole picture and set balanced priorities.

In some ways, we, along with the architects and builders of our buildings, seem to be stuck between a rock and a hard place: we need to make the indoor and outdoor environments simultaneously healthier. Yet they are so interdependent!

 We can still have energy-efficient buildings and create suitable environments for many of our beneficial, ‘old friends,’ i.e. the microbes, naturally hindering the unopposed propagation of the pathogenic, multi-resistant microorganisms.


Buildings as living ecosystems

If we wish to create greater and balanced microbial diversity in our buildings, we have to make sure our buildings have diverse materials, sufficient humidity and layout diversity, too. You’ve probably heard, variety is the spice of life. Well, that is every bit as true when it comes to the microbiome.

My TO DO list for healthy buildings

  1. Choose natural materials with porous surfaces for walls, ceilings, floors and furniture so there are sufficient moisture and nutrients to sustain good bacteria and viruses, enabling them to naturally suppress pathogenic microorganisms.
    Use nonporous, smooth synthetic materials sparingly and when, only for surfaces that see frequent contact and therefore need regular cleaning – e.g. handrails, door handles, taps and keyboards.

  2. Monitor and actively manage the indoor humidity throughout the year to make sure it stays within the healthy range of 40-60% relative humidity.

  3. Make sure inner spaces have sunlight and fresh air: natural light, ventilation and filtration are vital to promoting microbial diversity.

  4. Design interior layouts based on buildings’ users activities. Having only open-plan layouts promotes the spread of microbes, including the ‘bad guys.’ As always, diversity is better, for example, a mixture of smaller spaces and larger open rooms, etc.

  5. Use cleaning substances wisely. With the exception of hospitals, use detergents and chemicals to clean surfaces only when absolutely necessary. Otherwise, soap and water are perfectly adequate.

  6. Add some plants. They are a helpful medium, aesthetically, biologically, physically and emotionally. And they extract carbon dioxide while adding moisture via transpiration and microbes by means of the soil.

An inspiring public space: the Library of Congress in Washington, DC

Let’s apply what we know so we can learn more, while being more natural and holistic in our approaches!