Air Quality Basics
Why Indoor Air Quality Matters
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10 mins
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Published on
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Reviewed by the BREATHE editorial team
Quick Answer
Indoor air quality has a direct impact on how we feel, sleep, concentrate and perform every day. Most people spend around 90% of their time inside buildings, which makes the condition of indoor air more relevant to health than outdoor air quality for the majority of people, most of the time. Poor ventilation, everyday household activities and the materials buildings are made from can all push pollutant levels higher than those found outdoors. Improving indoor air quality does not require significant expense. Understanding what is happening and making a few consistent changes is often enough to notice a real difference.
TL;DR
- What it affects: Health, sleep, concentration, comfort and long-term wellbeing.
- Who it affects most: Everyone, but particularly children, older adults and people with respiratory conditions.
- Why it is often overlooked: Most indoor pollutants are completely invisible.
- Biggest improvement: Better and more regular ventilation.
- How to know what is happening: Continuous air quality monitoring.
Why indoor air quality matters
The air quality inside a building shapes how people feel during almost every part of their day. It influences how well they sleep, how clearly they think and how comfortable they feel at home, at work and at school.
Most people are aware of concerns about outdoor air pollution from traffic, wildfires or industry. Indoor air quality gets far less attention, despite the fact that most people spend the great majority of their waking and sleeping hours inside buildings. Research consistently shows that indoor air can contain higher concentrations of certain pollutants than outdoor air, particularly in homes and workplaces with limited ventilation.
The reasons indoor air quality matters are both immediate and long-term. In the short term, elevated CO₂ or VOC levels can reduce concentration, trigger headaches or disturb sleep. Over longer periods, sustained exposure to certain pollutants has been associated with more significant health effects. This is not purely a comfort issue.
Why we spend so much time indoors
The average person in a developed country spends around 90% of their time inside buildings. That figure includes time at home, at work, in schools, in shops and in cars and other enclosed spaces.
This is not a recent trend. Urbanisation, climate-controlled buildings, sedentary work and the growth of remote working have all contributed to people spending less time outdoors. During winter months, or in climates where outdoor conditions are extreme, the proportion rises further still.
The consequence is straightforward: the quality of indoor air matters more to human health than outdoor air quality does for most people, most of the time. Yet indoor air receives a fraction of the public attention and regulatory scrutiny that outdoor air does.
Everyday effects of poor air quality
Poor indoor air quality rarely produces one dramatic symptom. Instead it tends to create a low-level collection of effects that are easy to dismiss or attribute to other causes.
These can include difficulty concentrating, persistent tiredness, headaches in certain rooms, dry or irritated eyes and throat, worsened allergy or asthma symptoms, and that familiar sense of feeling more refreshed after opening a window. The connection between these experiences and air quality often goes unrecognised because the pollutants involved are invisible.
The table below shows some of the most common everyday sources of indoor pollution:
| Source | What it releases | Rooms most affected |
|---|---|---|
| Gas cooker | CO₂, NO₂, PM2.5 | Kitchen |
| Candles and incense | PM2.5, VOCs | Living room, bedroom |
| Cleaning sprays | VOCs | Kitchen, bathroom |
| New furniture and flooring | Formaldehyde, VOCs | Any room |
| People and pets | CO₂, moisture, dander | Living areas, bedrooms |
| Printers | VOCs, ozone | Home office |
| Damp and mould | Spores, moisture | Bathrooms, basements |
Who is most affected?
Poor indoor air quality affects everyone to some degree, but certain groups are more sensitive:
Children: Children breathe faster than adults relative to their body weight, which means they inhale proportionally more air and more pollutants. Developing lungs and immune systems are more vulnerable to sustained pollutant exposure.
Older adults: Age-related changes to lung function and immune response can make older adults more sensitive to elevated pollutant levels. Many also spend a higher proportion of their time indoors.
People with asthma or respiratory conditions: Elevated particulate levels, VOCs and humidity fluctuations can all act as triggers. Air quality management is particularly important for this group.
Pregnant women: Some research has suggested links between elevated indoor pollutant exposure during pregnancy and adverse birth outcomes, though more evidence is still needed in this area.
People with cardiovascular conditions: Fine particles (PM2.5) have been associated with cardiovascular effects in people with existing heart and circulatory conditions.
Healthy adults are not immune. The effects may be subtler, appearing mainly as reduced concentration, disrupted sleep or lower general comfort, but they are still present and measurable.
| Group | Main concerns | Why more vulnerable |
|---|---|---|
| Children | PM2.5, VOCs, formaldehyde | Higher breathing rate, developing systems |
| Older adults | CO₂, PM2.5, humidity | Reduced lung function, more time indoors |
| Asthma and allergy sufferers | PM10, PM2.5, VOCs, humidity | Known triggers for symptoms |
| Pregnant women | VOCs, formaldehyde | Potential effects on development |
| People with heart conditions | PM2.5 | Links to cardiovascular events |
Health effects versus comfort effects
It is useful to separate the effects of poor indoor air quality into two categories: health effects and comfort effects. Both matter, but they operate on different timescales.
Comfort effects happen at lower pollutant concentrations and tend to be reversible quickly. A stuffy feeling in a poorly ventilated room, dry air causing throat irritation, or a mild headache after a few hours at elevated CO₂ levels all fall into this category. They resolve when conditions improve.
Health effects are typically associated with higher concentrations, prolonged exposure or specific high-risk pollutants. Sustained formaldehyde exposure, chronically poor ventilation or repeated high PM2.5 episodes fall here. These are longer-term concerns that benefit from sustained monitoring and source control.
Most people's day-to-day experience of indoor air quality sits in the comfort zone: conditions that are not causing acute harm but are making their environment less comfortable and less productive than it could be. Monitoring reveals where those thresholds are being crossed.
Benefits of better indoor air quality
Improving indoor air quality
produces a range of practical, everyday benefits:
| Benefit | Who notices it most |
|---|---|
| Better sleep quality | Everyone, particularly in bedrooms with poor ventilation |
| Improved concentration and productivity | Office workers, students, remote workers |
| Fewer headaches | Anyone in regularly stuffy environments |
| Reduced allergy and asthma symptoms | Allergy and asthma sufferers |
| Greater comfort at home | All building occupants |
| More confidence in your indoor environment | Parents, caregivers, health-conscious households |
These benefits are not theoretical. Studies in offices and schools have consistently found that whenventilation improves and CO₂ levels fall, self-reported wellbeing and measuredcognitive performance both improve. The effect is not dramatic in any singleinstance, but it is repeatable and meaningful across large groups.
Simple ways to improve indoor air quality
The most effective improvements do not require significant expense:
Ventilate regularly: Open windows when outdoor conditions allow. Even brief periods of ventilation dilute indoor pollutants significantly. In airtight modern homes, mechanical ventilation or a heat recovery unit may be worth considering.
Use extractors while cooking and showering: Extractor fans remove moisture and combustion products at the source before they spread through the home. This is one of the highest-impact habits in most households.
Reduce source emissions: Choose lower-VOC paints and cleaning products where practical. Avoid burning candles or incense in poorly ventilated rooms.
Manage humidity: Aim for 40 to 60 percent relative humidity. A dehumidifier in a consistently damp room and adequate heating in winter both help.
Monitor what is happening: An air quality monitor replaces guesswork with data. It shows which activities drive pollutant spikes, whether ventilation is adequate and whether changes are working.
Consistency matters more than perfection. Better habits applied regularly tend to produce more noticeable results than occasional large interventions.
BREATHE RECOMMENDATION
The BREATHE Airmonitor Plus makes it straightforward to understand what is happening to the air in your home. Monitoring CO₂, PM1, PM2.5, PM10, TVOCs, formaldehyde, temperature and humidity in real time, it gives you the data to act when conditions change, rather than assuming the air is fine.
Frequently asked questions
Why does indoor air quality matter if my home looks clean?
Cleanliness and air quality are not the same thing. A visually tidy home can still have elevated CO₂ from occupants, VOCs from furniture and cleaning products, or fine particles from cooking. Most indoor air pollutants are invisible.
Does outdoor pollution affect indoor air quality?
Yes. Traffic emissions, pollen, wildfire smoke and industrial pollution can all enter buildings through open windows, ventilation systems and structural gaps. Outdoor air quality affects what comes in, particularly when windows are open or ventilation systems are drawing in outside air.
How quickly can indoor air quality change?
Very quickly in some cases. Cooking can raise PM2.5 levels within a minute or two. CO₂ builds more gradually over an hour or more in an occupied room. Some pollutants, like formaldehyde from furniture, off-gas continuously at lower levels over months or years.
Is poor indoor air quality only a problem in older buildings?
No. Newer buildings are often better sealed and insulated, which can trap pollutants more effectively than older, draftier buildings. Newer buildings also tend to have higher levels of off-gassing from fresh materials. Good ventilation is important regardless of the age of a building.
Can indoor plants improve air quality?
Some studies have suggested plants can absorb small amounts of certain VOCs, but the effect in real-world indoor conditions is very limited. The number of plants required to produce a meaningful improvement would be impractical for most homes. Plants have other benefits, but they are not a reliable air quality solution.
What is the single most important thing I can do to improve indoor air quality?
Ventilate. Opening windows
regularly and using extractor fans while cooking and showering has a greater
impact than any product purchase. Ventilation dilutes all pollutants
simultaneously rather than targeting one at a time.
Do I really need an air quality monitor?
You do not need one to take action, but a monitor tells you what is actually happening rather than leaving you to guess. It can reveal which activities drive pollutant levels up, whether your ventilation is adequate and whether the changes you make are producing results.
Why do I feel tired at my desk but more alert after going outside?
This is a common experience in poorly ventilated rooms. Elevated CO₂ and accumulated VOCs reduce alertness and make concentration harder. Outdoor air, where CO₂ is constantly diluted, provides an immediate contrast. Better desk ventilation can produce a similar effect indoors.
At what age should I start thinking about indoor air quality for my children?
From birth. Infants and young children spend the most time indoors and have the least control over their environment. Nurseries and bedrooms with good ventilation, low-VOC materials and well-managed humidity benefit children from their earliest months.
Is the air quality in my car relevant?
Yes. Car interiors can accumulate VOCs, particularly in newer vehicles, and studies have shown that exposure to traffic pollution is actually higher inside cars than on pavements alongside the same road. Ventilating car cabins regularly is worthwhile, particularly on longer journeys.
Sources: World Health Organization. WHO Global Air Quality Guidelines. Geneva: WHO Press, 2021. US Environmental Protection Agency. Indoor Air Quality. epa.gov/indoor-air-quality-iaq Sundell, J. et al. (2011). Ventilation rates and health: multidisciplinary review of the scientific literature. Indoor Air, 21(3), pp.191-204. Daisey, J.M., Angell, W.J. and Apte, M.G. (2003). Indoor air quality, ventilation and health symptoms in schools. Indoor Air, 13(1), pp.53-64. Satish, U. et al. (2012). Is CO2 an indoor pollutant? Direct effects of low-to-moderate CO2 concentrations on human decision-making performance. Environmental Health Perspectives, 120(12), pp.1671-1677.
At a Glance
- People spend around 90% of their time indoors.
- Indoor air quality directly affects health, sleep and concentration.
- Poor ventilation allows pollutants to build up quickly.
- Children, older adults and those with respiratory conditions are more sensitive.
- Monitoring gives you objective data rather than guesswork.
