Indoor air and health

Indoor Air Quality and Health — The Evidence

The evidence behind the air you breathe indoors.

InAir Indoor Air Quality and Health — The Evidence

Indians spend around 90% of their lives indoors, and in a sealed, air-conditioned home that air is largely the same air, recirculated. This page sets out what the published research actually says about that — carbon dioxide, fine particulates, airborne pathogens, allergens and sleep — with the citations, so you can check it yourself.

InAir supplies ventilation equipment. Nothing on this page is medical advice, and no InAir product diagnoses, treats, cures or prevents any disease. What the research below establishes is that indoor air quality is an environmental factor in health outcomes, and what our equipment does is change that environment. Decisions about a medical condition belong with a doctor.
Mechanisms

Five ways indoor air affects the people in a building.

Carbon dioxide and cognitive performance

Every exhaled breath adds CO₂ to a closed room. With two or three people asleep and the door shut, a bedroom typically passes 1,500 ppm before morning against roughly 420 ppm outdoors. The Harvard T.H. Chan double-blind study measured a 21% fall in decision-making scores at 1,000 ppm and about 50% at 2,500 ppm — and participants could not tell which air they were breathing.

1,500 ppm
typical sealed 3 BHK bedroom by 2am
-21%
decision-making at 1,000 ppm vs 550
under 800 ppm
held continuously with ventilation

Fine particulate matter and the cardiovascular system

PM2.5 is small enough to cross from the lung into the bloodstream. The WHO guideline is 15 µg/m³ over 24 hours; Delhi winters routinely run twenty to twenty-five times that. Long-term exposure is causally associated in the literature with cardiovascular disease, stroke and accelerated cognitive decline. Sealing a building does not exclude PM2.5 — it simply removes the route out.

15 µg/m³
WHO 24-hour guideline
300-400
Delhi winter PM2.5, µg/m³
99.97%
PM2.5 captured by HEPA-13

Airborne pathogens and dilution

ASHRAE, the WHO and the CDC each issued ventilation guidance during the COVID-19 pandemic, and ASHRAE Standard 241-2023 now sets quantitative ventilation requirements for infectious-aerosol control as a permanent standard. The mechanism is dilution: replacing room air lowers the concentration of airborne particles. It applies to influenza, RSV and tuberculosis just as it does to SARS-CoV-2.

ASHRAE 241
infectious aerosol standard, 2023
3 bodies
ASHRAE, WHO and CDC aligned
Dilution
the mechanism, not sterilisation

Allergens, humidity and volatile compounds

Dust mites and mould need humidity above roughly 60% RH to establish. Furnishings, paints, adhesives and cleaning products release VOCs continuously, and in a sealed room they accumulate because nothing carries them out. Filtration removes particulate allergens; only ventilation removes the gases and controls the moisture that lets biological allergens grow.

60% RH
threshold for mite and mould growth
VOCs
removed by air change, not filtration
MERV-13
pollen, mould spores, mite allergen

Sleep and next-day alertness

Controlled studies report improved sleep depth and next-day alertness when bedroom ventilation improves. A closed Indian bedroom commonly reaches 2,000 ppm CO₂ or more in the early hours. The reported change is usually described as waking more rested rather than sleeping longer, and it is typically noticed within the first week.

2,000+ ppm
closed bedroom, early hours
First week
when most people report a change
Continuous
ventilation runs while you sleep
Who it matters most for

Everyone breathes. Some people are more exposed than others.

Children and teenagers

They inhale roughly twice the air per kilogram of body weight that adults do, and their lungs keep developing into adolescence. Classroom CO₂ studies consistently show attention and recall declining as concentrations rise.

Elderly parents at home

People over seventy spend 85–95% of their time indoors, so indoor air is very nearly all the air they breathe. PM2.5 exposure is linked in the literature to cardiovascular disease and cognitive decline.

Asthma, allergies and respiratory conditions

HEPA-13 removes 99.97% of PM2.5, pollen, dust-mite allergen and mould spores, and continuous air change limits the humidity those allergens need. An environmental change, not a treatment.

Working from home

A closed study with the door shut passes 1,000 ppm within a couple of hours. The mid-afternoon slump in a small home office is very often an air problem rather than a sleep problem.

Newborns and new parents

Infants sleep 14–17 hours a day in one room, usually with the door closed. That room is effectively their entire environment for the first months.

Schools, clinics and offices

Occupant density is the driver. ASHRAE 62.1 sets ventilation per person for exactly this reason, and CO₂-linked demand control matches the rate to how full the room actually is.

Health questions

The questions people actually ask.

At the levels found in sealed Indian homes CO₂ is not acutely dangerous — the issue is chronic exposure. The Harvard T.H. Chan double-blind study (Satish et al., Environmental Health Perspectives, 2012) measured a 21% fall in decision-making scores at 1,000 ppm against a 550 ppm baseline, and around 50% at 2,500 ppm. Participants could not tell which air they were breathing. A closed bedroom with two or three people typically passes 1,500 ppm before morning.
You generally wouldn't, which is the difficulty. CO₂ is odourless and its effects are subclinical — you don't feel them acutely, you just perform slightly worse and wake up less rested. The reliable symptoms people report are morning grogginess, headaches on waking, an afternoon slump while working from home, and children struggling to concentrate. The only way to settle it is to measure, which is why our surveys include a CO₂ reading of your actual rooms.
By replacing air rather than cleaning it. The unit continuously supplies filtered outdoor air — around 420 ppm CO₂ — while exhausting indoor air carrying the CO₂ occupants exhale. Sizing to ASHRAE 62.1 sets the air-change rate against the number of occupants, and where a CO₂ sensor is fitted the unit modulates its rate to match actual occupancy instead of running flat out.
Diluting and removing airborne particles reduces exposure, and that is why ASHRAE, the WHO and the CDC each issued ventilation guidance during the COVID-19 pandemic. ASHRAE Standard 241-2023 sets quantitative ventilation requirements specifically for infectious-aerosol control. What ventilation does is lower the concentration of airborne particles in a room; it does not make a space sterile, and it is not a medical intervention or a substitute for one.
The reasoning was never specific to one virus. Influenza, RSV, tuberculosis and common respiratory infections all transmit partly through airborne particles, and the same dilution applies to all of them. ASHRAE 241 was written as a permanent standard, not an emergency measure. The broader case — CO₂, PM2.5, VOCs and humidity control — holds regardless of what is circulating.
It can change the environment, and that is all we claim. Nothing InAir supplies diagnoses or treats any condition, and decisions about asthma belong with a doctor. What the evidence establishes is that indoor particulate and carbon dioxide are environmental factors in respiratory outcomes. Filtered fresh air lowers both. Whether that helps a particular child is a question for their clinician.
They cover different ground. A purifier reduces particles in the air that is already in the room, which is genuinely useful. It cannot remove CO₂, it cannot exhaust VOCs from furnishings and cleaning products, and it cannot bring in oxygen-fresh air. In a sealed room a purifier will give you clean, stale air. Ventilation and filtration together give you clean, fresh air — which is why many homes run both.
It matters more for them than for most. People over seventy typically spend 85–95% of their time indoors, so indoor air is very nearly all the air they breathe. PM2.5 exposure is causally linked in the literature to cardiovascular disease and to accelerated cognitive decline, and elevated CO₂ measurably impairs cognitive performance. Improving the air is one of the few interventions that requires nothing of the person at all.
Three things. They inhale about twice the air per kilogram of body weight that adults do, so airborne pollutants land harder. Their lungs continue developing into adolescence, and studies associate long-term particulate exposure with reduced lung-function growth. And classroom and homework CO₂ studies consistently show attention and recall falling as concentrations rise — the same effect applies to a closed bedroom used for study.
There is reasonable published evidence that bedroom CO₂ affects sleep quality, with controlled studies reporting better sleep depth and next-day alertness when bedroom ventilation improves. In a sealed Indian bedroom CO₂ commonly reaches 2,000 ppm or more by the early hours. Customers most often describe the change within the first week, and describe it as waking more rested rather than sleeping longer. Individual experience varies.
A closed room with one person and the door shut climbs past 1,000 ppm CO₂ within a couple of hours, and the Harvard data puts a measurable cost on that — roughly a fifth of decision-making performance at 1,000 ppm. The familiar mid-afternoon slump in a closed study is very often an air problem rather than a sleep or caffeine problem. Continuous ventilation holds the room near outdoor CO₂ levels through the working day.
The main sources are set out in full on this page with citations and DOIs. In summary: Satish et al. (Environmental Health Perspectives, 2012, Harvard T.H. Chan) on CO₂ and decision-making; ASHRAE Standard 241-2023 on infectious-aerosol control; WHO and CDC ventilation guidance; WHO global air quality guidelines for PM2.5; and ASHRAE 62.1 for ventilation rates. Everything on this page is published, third-party research — we would rather you verified it than took our word for it.
Yes — commissioning includes before-and-after measurement of CO₂ and PM2.5 in the actual rooms, and where an IAQ sensor is installed you can see the readings continuously yourself. Our case studies carry the recorded figures for specific installations. We would rather show you measurements from a home like yours than quote a laboratory number.
Sources

Every claim on this page, sourced.

All of it is third-party published research and standards. None of it is ours. We would rather you verified it than took our word for it.

CO₂ and cognitive performance
Satish U, Mendell MJ, Shekhar K, Hotchi T, Sullivan D, Streufert S, Fisk WJ. “Is CO₂ an Indoor Pollutant? Direct Effects of Low-to-Moderate CO₂ Concentrations on Human Decision-Making Performance.” Environmental Health Perspectives 2012;120(12):1671–1677. Harvard T.H. Chan School of Public Health.
DOI: 10.1289/ehp.1104789
Double-blind. 21% reduction in decision-making scores at 1,000 ppm against a 550 ppm baseline; approximately 50% at 2,500 ppm. Participants could not identify which condition they were in.
Infectious aerosols and ventilation
ASHRAE Standard 241-2023, “Control of Infectious Aerosols.” American Society of Heating, Refrigerating and Air-Conditioning Engineers, 2023.
ASHRAE 241-2023
Establishes quantitative ventilation requirements specifically for infectious-aerosol control, as a permanent standard rather than emergency guidance.
Ventilation guidance, global health bodies
WHO, “Roadmap to improve and ensure good indoor ventilation in the context of COVID-19” (WHO/2019-nCoV/ventilation/2021.1). CDC, “Ventilation in Buildings” (updated 2023). Morawska L. et al., “Airborne transmission of SARS-CoV-2,” Environment International Vol 139, 2020.
WHO / CDC / Environment International
Three independent bodies converged on improved ventilation as a primary infection-control measure.
Particulate matter exposure limits
World Health Organization Global Air Quality Guidelines, 2021.
WHO AQG 2021
PM2.5 guideline of 15 µg/m³ over 24 hours and 5 µg/m³ annual mean. Indian urban winter readings frequently exceed the 24-hour figure by a factor of twenty or more.
Ventilation rates for acceptable indoor air quality
ANSI/ASHRAE Standard 62.1, “Ventilation and Acceptable Indoor Air Quality.”
ASHRAE 62.1
The basis on which InAir sizes every system: ventilation rate per person plus an allowance for floor area.

Want to know what your own rooms measure?

Our engineers record CO₂ and PM2.5 in your actual rooms during the site survey, before anything is quoted. It is free, and there is no obligation.

Book a free site survey

Further reading