Spring! Welcome back! The winter is over. The windows can be opened wide again, and the stale air replaced with something fresher. While most of us already realise that that’s probably good for us, a study by the Harvard School of Public Health recently revealed that the quality of the air we breathe indoors can have an alarming effect on our performance.


In the course of the past winter, the indoors air steadily accumulated – simply through our respiration, and because floor coverings and new furniture contribute to the ‘invisible’ contents of our living and working spaces. “But I don’t smell or notice it,” one might say. But that what’s so insidious about it – it goes on unnoticed. And staying/working indoors (or worse: working while sitting) doesn’t make matters any better. Are we more productive because we’re avoiding being distracted by the sociable atmosphere of an outdoor café? That argument holds no water, unfortunately. On the contrary, both our senses and performance suffer dramatically by remaining indoors. What’s more: in busy cities, the air quality indoors is worse than that outdoor – five to seven times worse, despite the introduction of fresh air through mechanical ventilation. And because we spend most of our time indoors, the consequences for our health are by no means negligible.

How could this happen? Well, since the 70s, due to increasing energy prices, buildings have been made ever more airtight. Air exchange was left to ventilation systems that let in fresh air with a certain set frequency – or just pumped the same air round and round. This was not without negative consequences. In the 80s, the first effects from our well-insulated, but, as it turns out, unhealthy buildings could be observed. Complaints such as sleeplessness, irritations, difficulty concentrating, fatigue and nausea were increasingly attributed to the poor quality of the interior climate, complaints now subsumed under the term sick building syndrome.

So how can we improve our ‘interior climate’? It was not long before the first ventilation norm (ASHRAE) saw the light. From the start of the new millennium, the insight that when designing a building, it isn’t enough just to determine the environment indoors, but that an exchange with the outdoor environment must be provided as well, led to more comprehensive green norms (LEED and BREEAM). Sustainable design came on the scene and the first green buildings went up.

Most people are now aware of the health risks from dubious indoor air quality. For both our own health and that of our employees, clients, patients and pupils. And we know that it negatively affects both (company) results and learning performance. What’s strange, though, is that, despite this, as Harvard’s Joseph Allen rightly has observed, ‘investing in air’ is still often regarded as a secondary priority: “We spend 90% of our time indoors and 90% of the costs of a building are the occupants, yet indoor environmental quality and its impact on health and productivity are often an afterthought”.

Investing in indoor air quality pays off

Because no hard statistics were as yet available concerning the relevant effects, Allen and his team devised their own study. They went in search of facts and figures about the relationship between ventilation, indoor air quality and its effects on how we process knowledge and information, i.e., our cognitive processes. They studied nine cognitive functions among twenty-four subjects. The subjects carried out their normal activities while researchers subjected them to a range of indoor climatic effects, such as VOCs and CO2 levels. Different ventilation norms were also employed: the conventional one, the Green Norm and Green+, the last-mentioned approach involving Green Norm ventilation with fresh outdoor air added. The results of this investigation were published in October 2015 .

Indoor air: a cocktail of VOCs and CO2

VOC stands for volatile organic compounds, which occur in many man-made materials. These chemical substances become airborne through evaporation. You can smell them. Examples are new furniture, glues and so-called air-fresheners. But after a period of time, some can no longer be smelled while they continue for years to evaporate completely. Particularly vicious is formaldehyde, a substance that emanates from building materials such as MDF and chipboard. If in sufficiently high concentration, these can cause severe harm, such as respiratory problems, irritations and headache, or, in the case of extremely high exposure, occupational illnesses, such as OBS in the case of house painters. VOC concentrations in modern buildings are, generally speaking, quite low. Nevertheless, there are increasing indications that where constant exposure is involved, including in low concentrations, the sick building syndrome mentioned above can result.

Back for a moment to the Harvard study again. It involved making measurements for only six days over a period of two weeks. While already prior to carrying out the study, the researchers had expected VOCs to have deleterious effects, what came as a surprise was the effect of CO2 (carbon dioxide), which previously had seemed relatively benign. It turned out to have an influence on as many as seven of the nine functions tested. Thus we ourselves are the biggest indoor-air polluters – with every breath we take.

When I read their Top Three most obvious ways to improve performance (measured in terms of conventional ventilation), I immediately got shortness of breath. Hard to believe what we surrender in human potential by investing insufficiently in fresh air. You can be the judge:


Certain indoor conditions clearly have very negative effects on our performance. A good ventilation system can substantially contribute to neutralising these. The results of the Harvard study show that even small modifications to our interior climate can have a big effect on such cognitive functions as our ability to take decisions. They also tend to indicate that a health interior climate can even lead to a substantial improvement in our performance, our ability to learn and our physical well-being.

Just as good indoors as out?

So shall we just wait for the newest ventilation technologies to arrive? Certainly not! You can start improving your interior climate now, in an extremely simple and natural manner: by opening your windows with reasonable regularity. And if that’s not possible, get some plants – it has been proven incontrovertibly in a number of different studies that they are naturals when it comes to dust removal, air purification and stress reduction.

potjes op de vensterbank
Residents of a space furnished for daytime activities by Studio School, grow plants for fresh air. Photo: Anselien School

There’s more than one way to generate healthy indoor air.