Is your kitchen more polluted than your high street?

People tend to be aware that breathing in traffic fumes isn't ideal, but what about everyday cooking and the impact it has on air quality in the home? How can it affect your health?

Outdoor pollution has been a source of concern and cause for policy interventions for a number of years now – there are set levels that shouldn’t be exceeded for a raft of pollutants from carbon monoxide, particulate matter and nitrogen dioxide.

Inside the home, however, has historically been a different matter. Public health policy makers don’t tend to involve themselves in what goes on behind closed doors. But we spend up to 90% of our lives indoors and, for many, a lot of that is inside our own homes. 

One of the biggest sources of indoor pollution comes from something we do every day – cooking. Particularly on the hob, where cooking takes place in an open environment and its byproducts are released into the air around you. 

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Particulate matter and nitrogen dioxide

Professor Sir Chris Whitty, England’s chief medical officer, made air pollution the subject of his 2022 annual report. This linked long-term exposure to outdoor air pollution to between 26,000 and 38,000 deaths a year, and attributed many people’s avoidable ill health to it. The public health burden if you include indoor air pollution is likely to be significantly higher.

Two of the most damaging pollutants are particulate matter (PM) and nitrogen dioxide.

• Particulate matter (PM2.5)

PM is everything in the air that is not a gas and some of these small particles are known to be toxic. PM2.5 can be particularly damaging as the tiny size of the particles can travel deep into lungs and enter the bloodstream to reach all organs of the body. Here, they induce changes that promote many different diseases such as Parkinson’s disease, diabetes, lung cancer, chronic obstructive pulmonary disease (COPD) and heart disease, and impacts on the reproductive system and developing child in pregnancy.

• Nitrogen dioxide (NO2)

Nitrogen dioxide (NO2) is a significant contributor to children developing asthma, as well as exacerbating other respiratory conditions in both children and adults.  

The health impacts of indoor air pollution

Professor Sir Stephen Holgate, clinical professor of immunopharmacology at the University of Southampton, is a former chair of the Committee on the Medical Effects of Air Pollutants (COMEAP), which advises the government on all matters concerning the health effects of air pollutants. He told us there’s increasing evidence that activities that affect air quality in the indoor environment, such as cooking/combustion, can create particles even smaller than those found outdoors. 

Some of these tiny particles can bind or chemically react with other pollutants such as volatile organic compounds (VOCs) and NO2, making them potentially even more damaging for our health. Professor Holgate says, ‘The toxic payload of these particles when breathed in could be very high, as they can travel so deep inside the body.'

However, while we know these particles can make their way into the body, there are still significant knowledge gaps in how air pollution actually impacts us once it's there. Scientists are trying to find an answer. It’s difficult to attribute ill health to one specific air pollutant, as it’s near impossible to isolate them (and their effects) from each other. Throughout our lifes, humans move constantly between different cocktails of chemicals from different sources – diesel engines, wood smoke, cooking and cleaning products to name a few. 

Different impacts may be caused by the acute effects of peak exposures and the long-term effects of sustained, low-level exposure, or repeated exposure at higher levels.

To date, most existing research is based around epidemiology – which makes links between increased air pollution and the prevalence of asthma, for example. But this can’t give us definitive information about what a particular pollutant is doing to the human body with chronic exposure. To answer this, a long-term project called HIP-Tox is running at the University of Manchester. Led by Professor Gordon McFiggans, the study aims to establish a hazard identification platform using toxicological studies.

At the moment, scientists simply don’t know if the effects of indoor and outdoor PM are the same. We assume pleasant cooking smells are not as harmful as acrid diesel ones, but Professor McFiggans says: ‘We’ve no idea whether our noses are deceiving us.’ 

Current WHO guidance limits are set on the basis that there are no safe levels of air pollution.

Gas hobs and air pollution

Gas hobs have had a lot of negative attention in the press. Recent studies have highlighted the high levels of nitrogen dioxide (NO2) that they put out – a byproduct of burning natural gas. 

A 2023 study carried out over seven countries by CLASP, a global non-profit campaigning for efficient appliances, found that over half of UK households that used gas exceeded WHO daily guideline NO2 values and 25% exceeded the UK/EU hourly limits. 

All cooking, whether using a gas or electric hob or other appliances such as ovens and toasters, can give off pollutants — from volatile organic compounds (VOCs) to particulate matter. 

The act of heating food creates some of these pollutants. Frying generally causes the highest levels and boiling or steaming the least. The INGENIOUS project – led by Professor Nicola Carslaw at the University of York – measured air pollution, including PM2.5, in 310 Bradford homes and found peak indoor concentrations of PM2.5 exceeding 500µg/m³ (that's micrograms per cubic metre of air) when cooking food.

Some studies have found that levels of VOCs and PM are increased by using gas hobs as compared to other cooking appliances, due to the presence of a naked flame. Gas stoves can also be a source of benzene exposure which is a known carcinogen.

Professor Frank Kelly of Imperial College London, and another former COMEAP chair, will shortly be publishing the results of a major air quality study called WellHome. This looks at the impact of indoor air pollution on over 100 households, half of which included an asthmatic child. Professor Kelly says: ‘Gas hobs and ovens are a major source of indoor air pollution, including NO2, which can both exacerbate existing health conditions and potentially lead to new respiratory illnesses.' 

Gas vs induction hobs: we explain the differences between gas and induction hobs

Our air pollution experiment

We wanted to see for ourselves how everyday cooking activities affect levels of NO2 and PM2.5 in the home. 

In November 2024, we gave air quality monitors to five volunteers – four with gas hobs and one with induction – and asked them to carry out a variety of cooking scenarios in addition to their normal usage over the course of a week. All of them used extractor hoods. They were asked to keep windows and doors shut, aside from one test scenario where they fully ventilated the kitchen. 

NO2

NO2 showed significant peaks when cooking in homes with gas hobs. The home with an induction hob stayed at a pretty steady base level throughout the time the monitor was in use. In the homes with gas hobs, levels of NO2 increased in line with the amount of time that gas was used for or the number of gas rings used. In our slow cooking scenario (using one ring), all participants’ NO2 levels more than doubled. 

Our multi-zone cooking scenario (cooking on several rings) also caused significant increases in NO2. Once levels of NO2 had spiked, they remained elevated for significant periods of time – often several hours. If you’re spending your evening in the same room where you’ve cooked (as with open-plan homes), you could be exposed to sustained elevated levels well in excess of the guidelines. 

For one of the cooking scenarios, we also asked people to move their monitors into an adjoining room, or into the living area if their house was open plan. Levels of both NO2 and PM2.5 still recorded high peaks and elevated levels for some hours afterwards, showing that air pollution spreads through your home rapidly. Peak levels and average of NO2 regularly exceeded the WHO guidance levels, which is a mean average over 24 hours of 25µg/m³ (micrograms per cubic metre of air). 

This graph shows the NO2 levels from a base of zero 10 minutes before cooking began to 180 minutes afterwards:

It must be noted that although the air quality monitors we used are models used in scientific observational studies, ours weren’t scientifically calibrated or recalibrated each time they entered a new home. 

There was some variation in readings between the two monitors we used, particularly with NO2 readings. One of the monitors consistently recorded higher starting base levels. So our graph showing NO2 levels when slow-cooking shows how they changed compared to the base level in each property, which we have adjusted to zero.  

PM2.5

PM2.5 rose in response to almost any cooking in our study, but frying in oil caused huge spikes. One person experienced a peak of nearly 650µg/m³ (the WHO 24-hour mean guidance limit is 15µg/m³) when frying Padron peppers. Another experienced nearly 600µg/m³ when frying peppers and tomatoes. Two people had peaks of nearly 500µg/m³ when cooking fry-ups. 

 Base levels before cooking varied from less than 1µg/m³ to no more than around 20µg/m³. Nearly all volunteers experienced peaks of over 100µg/m³ on several occasions when cooking. Once spiked, levels remained elevated for a long time. We averaged out the PM2.5 over a 24-hour period for the five days each person used the air-quality monitors. One household averaged over the WHO guidance limit on four days. Two other homes exceeded the limit on two days. 

This graph shows the PM2.5 levels from 10 minutes before cooking began to 120 minutes afterwards:

For context, over the period that volunteers were testing their indoor air pollution, air pollution levels near the Which? office, on London’s notoriously busy Marylebone Road, were as follows: average NO2 over an hourly mean for November 2024 was 33µg/ m³; average PM2.5 over a 24-hour mean for November 2024 was 14µg/m³.

What should you do about indoor air pollution?

There are simple measures you can take to improve the air quality when you cook using your hob.

1. Use your extractor hood

Make sure you use your extractor hood every time you cook and cook on back burners where the hood will be more effective. Extractors are much more effective if they’re vented outside, instead of recirculating the air. Higher fan settings will work best. Clean your extractor hood often (some mesh panels can be put in the dishwasher – check the instruction manual) and replace the filters every six months.

Read more: how to buy the best cooker hood

Monica Mateo-Garcia of Birmingham City University, co-founder of the Centre for Future Homes, says the best practice – popular in Germany – is called 'Stoßlüften', or ‘shock ventilation’. This involves fully opening all windows and internal doors in a home for a few minutes on a dry day, for a quick exchange of air and to remove indoor pollutants. This is a more energy-efficient way of ventilating than keeping some windows a little bit open all the time, as less heat is lost.

2. Other ventilation options

Shock ventilation might not be such a good option if, for example, your house is next to a busy road with high traffic pollution. HEPA air purifiers can do a good job of removing PM from the air, as they can trap fine particles. They won’t help for NO2 as it’s a gas. Mechanical air ventilation systems are another possible and effective option. UV air purifiers aren’t recommended, as they can produce dangerous levels of ozone (O3) if misused.

Read more: how to buy the best air purifier

3. Upgrade to an induction hob

Swapping from gas to an induction hob will remove much of the NO2 from your home environment and could reduce your exposure to PM. It also reduces your greenhouse gas emissions. Your existing gas supply will need to be capped off by a Gas Safe engineer and you’ll need to ensure your current electrical connection matches your new hob’s requirements.

Get more information about how to buy the best hob and see the best induction hobs for 2025 in our test results.