Cooking with a gas hob can cause more indoor than levels on one of the UK's busiest roads, a new investigation has found.

Consumer group Which? examined how everyday cooking activities affect levels of pollution in the average home. They looked specifically at Nitrogen Dioxide (NO2) and fine particulate matter (PM2.5) - two of the most damaging air pollutants found both indoors and outdoors.

Air quality monitors were given to five volunteers – four with gas hobs and one with an induction hob– 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 also asked to keep windows and doors shut, aside from one test scenario where they fully ventilated the kitchen.

Those using a hob experienced PM2.5 peaks of over 100µg/m³ on several occasions, and one volunteer experienced a peak PM2.5 of nearly 650µg/m³, (the 24-hour mean guidance limit is 15), when frying. Another experienced nearly 600 when frying. Two volunteers also had peaks of nearly 500 when cooking a fry-up.

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Over the period that volunteers were testing, 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

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

At the moment, scientists simply do not know if the effects of indoor and outdoor PM are the same, but current WHO guidance limits are set on the basis that there are no safe levels of air pollution.

Emily Seymour, Which? Energy and Sustainability Editor, said: “It’s shocking to think that something as routine as cooking dinner could be releasing harmful pollutants into our own homes, but our snapshot research shows that once it spikes, air pollution can spread rapidly through the house and linger for long periods of time.

“We still don’t know the full impact of indoor pollutants on our health but if it is something you are concerned about, ventilating by using your extractor hood and opening windows can make a big difference. If you are using a gas hob you could consider switching to induction when you next need to replace your hob.”

A study earlier this year found that pollution from gas cookers cuts short the lives of nearly 4,000 people in the UK each year, scientists have found. The fume levels increase in poorly ventilated homes and during longer cooking sessions.

Dr Juana Maria Delgado- Saborit, from the University Jaume I in Spain, said: "The problem is far worse than we thought." She added that modelling suggests the average home across half of Europe breaks World Health Organisation limits.

About a third of British homes cook with gas. The cookers leak powerful greenhouse gas methane even when switched off.

Air pollution is considered the biggest environmental health risk.