Indoor air quality and cognitive performance: the office, school and home evidence

Indoor air quality has long been treated as a respiratory and allergic concern. The evidence accumulated over the last decade has added a second dimension: cognitive performance. CO2 concentrations that occur routinely in poorly ventilated meeting rooms, classrooms, and home offices are now associated with measurable decrements in decision-making, response time, and complex task performance. Volatile organic compounds and fine particulate matter add to the picture, with effects that compound on each other.

This article summarises the evidence base, sets out what the Harvard COGfx studies and successor work have shown, and gives practical guidance on measurement for workers, parents, and people responsible for retirement housing.

The Harvard COGfx evidence

The COGfx studies, conducted at the Harvard T.H. Chan School of Public Health, were among the first to demonstrate causal rather than associational effects. Participants were exposed to controlled indoor environments at varying CO2, VOC, and ventilation rates and tested with a validated cognitive battery. The results showed that across nine domains — including basic activity, applied activity, focused activity, task orientation, crisis response, information seeking, information usage, breadth of approach, and strategy — performance declined at higher CO2 concentrations and at lower ventilation rates, with the largest decrements seen in the higher-order strategy and crisis-response domains.

The study also showed that the effect was not subtle. Moving from a CO2 concentration of around 550 ppm — typical of a well-ventilated outdoor-equivalent environment — to 1,400 ppm, which is common in poorly ventilated meeting rooms, produced cognitive performance decrements on the order of 15 to 50 per cent depending on the domain. Subsequent field studies in offices, schools, and aircraft have broadly confirmed the direction and approximate magnitude of the effect.

What the indoor air typically looks like

Real-world measurements of CO2 and PM2.5 in UK indoor environments are not reassuring. A typical poorly ventilated classroom in winter, with the windows shut to retain heat, will sit at 1,500 to 2,500 ppm CO2 for sustained periods. A home office in a poorly ventilated bedroom with the door shut will reach 1,800 to 2,200 ppm within an hour. A well-ventilated open-plan office with mechanical ventilation operating to current building regulation standards will sit in the 700 to 900 ppm range. The outdoor baseline is approximately 420 ppm.

The implication is that a substantial share of the UK's knowledge-economy work, and a substantial share of its schoolchildren's learning, is taking place in environments where the cognitive evidence base predicts measurable performance loss. The effect is not equally distributed: older buildings, retrofitted buildings where ventilation was not adequately addressed, and densely occupied rooms are disproportionately affected.

Implications for working from home, schools and retirement housing

For people working from home, the practical question is whether the room they work in is adequately ventilated. The single most useful action is to open a window for a period each morning, and ideally to have a cross-flow path established when the room is occupied for sustained periods. Where this is not feasible — older flats with single-aspect rooms, urban locations with noise or air-quality concerns from the outdoor air — a heat-recovery ventilation unit (MVHR or single-room MEV with heat recovery) is the standard engineering response.

For schools, the issue has been recognised in successive Department for Education guidance documents and in post-pandemic monitoring programmes that distributed CO2 monitors to many state schools. The clinical and educational case for improving classroom ventilation is now reasonably settled; the operational challenge is funding and retrofit.

For retirement housing the picture is somewhat different. Older residents are often more sensitive to draughts and cold than to elevated CO2, and the trade-off between ventilation and warmth is real. The right answer is not less ventilation but heat-recovery ventilation, which delivers fresh air without losing the warmth of the displaced air. PAS 2035 retrofit assessment will identify this as part of the whole-house picture.

Practical measurement at home

A consumer-grade CO2 monitor with NDIR sensing technology is now inexpensive and reliable. The advice for a household considering one is to look for NDIR (non-dispersive infrared) rather than electrochemical sensing — the former is more stable over time and less prone to drift — and to place the monitor at breathing height in the most-used room rather than at floor or ceiling level. A weekend of measurements will give a clear picture of where the household sits. The table below sets out indicative interpretation thresholds.

For a small number of pounds a week, a household can run a monitor with a memory card or wifi connection that logs trends over weeks rather than reading instantaneous values. The trend is more informative than the spot value: a room that touches 1,500 ppm briefly during a meeting and then returns to 700 ppm is in a different category from one that sits at 1,500 ppm all day. PM2.5 monitors of similar cost are also widely available and are particularly useful in urban locations and in households where solid-fuel burners are in use.

VOCs, PM2.5 and the wider air-quality picture

CO2 is a useful proxy for ventilation but is not itself harmful at indoor concentrations. The air-quality concerns that matter independently are volatile organic compounds (VOCs) — released by paints, furnishings, cleaning products, and combustion sources — and fine particulate matter (PM2.5), which enters from outdoor air and from indoor combustion. The cognitive evidence base on VOCs is somewhat smaller than that on CO2 but consistent in direction; the COGfx studies manipulated VOCs alongside CO2 and showed independent decrements at higher concentrations.

The main indoor sources of PM2.5 in UK homes are wood burners, gas hobs, candles, and incense. Wood burners are the largest single source in the homes that have them, with measured indoor concentrations during operation routinely exceeding the WHO outdoor air quality guideline. The implication for households with cardiovascular or respiratory concerns is that wood burner use should be reviewed as part of any wider housing-and-health intervention.

The role of cooking is often underestimated. Gas hob use produces nitrogen dioxide and PM2.5 in concentrations that would be regulatory exceedances if measured outdoors. The single most useful intervention is a working extract hood vented to outside, used routinely during cooking. Many UK kitchen extract hoods are recirculating rather than ducted; where this is the case, the hood is largely cosmetic for air-quality purposes.

Implications for clinical practice

The clinical question that follows from the indoor air-quality evidence is whether ventilation should be treated as a modifiable risk factor in routine practice. The answer in 2026 is a qualified yes for specific patient groups: people with poorly controlled cognitive concerns, people with respiratory conditions whose exacerbation pattern follows time spent indoors, occupants of retirement housing where reduced cognitive performance has been noted, and children with attention or behavioural concerns whose schools or homes are known to be poorly ventilated.

The cleanest clinical signposting is to a competent whole-house assessment. PAS 2035 includes ventilation as a first-class assessment domain, and a competent assessor will measure and report on the existing ventilation rate before specifying any thermal works. The point worth emphasising in a clinical letter is that ventilation should not be an afterthought to insulation — the two need to be designed together.

For workplaces, the relevant standard is broadly BS EN 16798 and CIBSE guidance, which set ventilation rate targets per occupant. Where an occupational health concern is raised, the appropriate next step is engagement with the building's facilities management rather than individual remediation; the resolution lies in the building services rather than in the individual.

Indoor air quality is one of the more easily measured housing exposures, and the cognitive performance evidence is now strong enough that ventilation should be treated as a first-class concern in any serious whole-house retrofit. A CO2 monitor in the home office and a willingness to open the window are the easiest first steps. Where the building fabric makes that impractical, heat-recovery ventilation is the engineering answer, and PAS 2035 is the standard that ensures it is integrated with the rest of the thermal and moisture picture rather than added as an afterthought.