Being inside with the windows closed does not completely protect you from the smoke caused by wildfires, early findings by University of Manchester researchers suggest.
And opening windows during hot weather, they show, almost certainly exacerbates the problem of indoor air pollution caused by the fires.
The University’s Cystic Fibrosis Hub Air Quality Research team analysed real time indoor air-quality records from 23 Greater Manchester homes monitored between 1 and 26 July 2026, during two periods of wildfire activity in the nearby Pennine hills.
Every monitored home in the Cystic Fibrosis Trust funded study exceeded the World Health Organization’s 24-hour guideline for fine particle pollution on 17 July, when outdoor smoke levels peaked.
The preliminary analysis, which has not yet undergone peer review, also showed when households opened widows as temperatures climbed to over 33C , the problem seemed to get worse.
Dr Congbo Song, based at The University of Manchester and the National Centre for Atmospheric Science (NCAS), led the analysis of PM2.5, particles produced by smoke small enough to travel deep into the lungs, where they can harm health.
During the wildfires, overnight bedroom PM2.5 spiked from an average of 2.7 micrograms per cubic metre to 7.8 with windows closed and 11.8 with windows open. Closing windows reduced exposure, but levels remained 2-4 times higher than normal.
In some homes, concentrations in the bedroom overnight rose to well over 100 micrograms per cubic metre, many times higher than the levels normally recorded in those homes.
Levels of indoor-generated pollution, such as volatile organic compounds and carbon dioxide, actually fell during this period as participants opened windows to cool their homes, allowing the outdoor pollution in.
The researchers say that following the UK Health Security Agency’s guidance on wildfire smoke by staying indoors and closing windows should help reduce the pollution.
Levels, they say, did not rise as much in homes where windows appear to have remained closed though this did not prevent all outdoor smoke pollution from getting in.
The researchers are also currently working on a Greater Manchester Local Innovation Partnership funded study, the Retrofit Advanced Materials and Manufacturing Innovation Centre to investigate measures that may help further combat indoor pollution, for example during periods of wildfire, and during intensely hot weather.
That could include the use of air purification and integrated ventilation systems, improved sleeping arrangements and other measures.
One of the researchers from The University of Manchester, Professor Alex Horsley, said: “These findings show the difficult challenges that people face during periods of wildfires and high environmental temperatures.
“Following the simple but often repeated instruction of going indoors and shutting the windows will only give you some protection from wildfire smoke, and keeps heat in the home. Both smoke and heat can make breathing worse for those with chronic lung conditions.
“During July’s fires, in every home we monitored we found the effects of smoke was present indoors at potentially harmful concentrations levels, especially during periods when the heat forced people to open windows.
“We saw this in homes up to 60km away from the wildfires on the moors outside Manchester.”
Dr Thomas Bannan, lead Environmental researcher for the group said: “The findings support advice to close windows while smoke levels are high, but show that this cannot completely prevent smoke infiltration and may increase the risk of overheating.
“The challenge is that this advice can be difficult to follow during very hot weather, particularly in homes that are prone to overheating.
“We need clearer, evidence-based guidance that helps households reduce exposure to both smoke and heat. I hope this new data can support these decisions.
“We are now investigating practical measures, including air filtration and approaches to keeping homes cool, so that people – especially those with existing respiratory conditions – have better options during future extreme events such as these.”
Dr Bannan added: “Wildfire smoke contains tiny particles and gases that can irritate the lungs and make respiratory conditions such as cystic fibrosis, asthma and COPD worse.
“Exposure to wildfire smoke can increase symptoms including coughing, wheezing, breathlessness and chest tightness, and may trigger severe flare-ups that require medical treatment.
“That is why people with existing respiratory diseases as well as children, older people and other immunocompromised people are also at greater risk of respiratory infections, hospitalisation and other serious health complications during wildfire events.”
Dr Sharon Weinberg, a clinical research fellow at The University of Manchester added:
said: “While our study examines the impact of PM2.5 on lung health, poor air quality affects far more than the lungs.
“Elevated PM2.5 exposure is known to increase the risk of cardiovascular events-including heart attacks, strokes, and thrombosis.
“It is also associated with headaches and migraines, highlighting that the health consequences of air pollution extend well beyond people with chronic respiratory disease.”
Laura Beattie, who has cystic fibrosis and is taking part in the study, said: “I found it really hard during the heatwave and the wildfires.
“You could see and smell the smoke for days, and it made my breathing worse. I was more breathless, and had to restrict myself to staying indoors. I also noticed that my sputum went dark from the smoke – I’ve never seen it like this before.
“We can all see wildfires becoming more common, and research like this is so important for people like me with chronic lung conditions.”
- The CF Tracker study is still recruiting people with CF across the UK, including in the Manchester and Merseyside regions where the air quality monitoring is included as an optional part of the study. The Pulse-CF Innovation Hub is part of the Translational Innovation Hub Network for CF Lung Health & Infection, funded by Cystic Fibrosis Trust and LifeArc. Though these findings are not yet peer reviewed, the research team felt it was in the public interest to release the figures.
