A leading respiratory expert at University Hospital Southampton (UHS) has warned of the “invisible threat” of indoor air pollution – with the UK “sleepwalking” into crisis.

Dr Thom Daniels, consultant respiratory physician at UHS, said the consequences could be far-reaching as emerging research suggests indoor air pollution may pose even greater risks to health than pollution outside.

The warning comes as the Royal College of Physicians (RCP) issues a new report that links air pollution to 30,000 deaths in the UK each year, which they estimate costs the economy and the NHS more than £27 billion annually.

The report identifies indoor air pollution as an escalating public health concern, emphasising its disproportionate impact on the most deprived communities – those who contribute least to emissions yet suffer the worst health outcomes.

Exposure can trigger short-term respiratory symptoms, exacerbate conditions like asthma and allergies and contributes to the development of many long-term illnesses – it has been deemed the largest environmental threat to human health according to the World Health Organisation (WHO).

Last year, the WHO said fuels and technologies used in and around the home contain a range of health-damaging pollutants which penetrate deep into the lungs and enter the bloodstream.

Speaking on Clean Air Day, the UK’s largest air pollution campaign, Dr Daniels said: “While outdoor air pollution is widely recognised and understood, the dangers of indoor air pollution remain largely overlooked – and I worry we’re sleepwalking into another microplastics-style crisis if we don’t act now.”

Indoor air pollution can cause headaches, eye and throat irritation and coughing. Over time, it can lead to, or worsen, chronic conditions like asthma and COPD, while increasing the risk of heart attack, stroke, cardiovascular disease, dementia and lung cancer.

He said: “A simple way to visualise just how concentrated indoor air pollution can be is to think of those sunny days when sunlight streams through a window, showing tiny particles dancing in the air. Many recognise these as “just dust” – but much of it may be harmful air pollutants. It’s quite alarming when you realise what you’re breathing in.

“Although many worry about outdoor air pollution, we spend 90 per cent of our time indoors, yet rarely think about the quality of the air we’re breathing. This is an invisible threat to health in every home.”

Dr Daniels has been conducting personal studies using a handheld device that measures airborne particulate matter - tiny particles that range from a few nanometres (about the size of a virus) to around 100 micrometres (about the thickness of a human hair).

Particulate matter and harmful gases come from human activities such as using gas hobs or wood burning stoves in your home, as well as natural sources, formed through chemical reactions in the atmosphere.

He added: “I was shocked by how often my device showed that air pollution levels indoors were worse than outside – even when the air looked clear. Once, after burning some toast, the readings shot off the scale. Even two hours later, the air quality was still poor, despite ventilation.”

He emphasised that this issue goes far beyond those with existing lung conditions. “It is a hidden threat to everyone. Without action, indoor air pollution could have devastating long-term consequences for everyone.

“Particulate matter has been found in almost every organ including the brain, in blood vessels and even in the testicles and placenta – potentially affecting foetal development. We don’t yet know for sure what it is doing there, but it can’t be good for you. But by making a few small changes, we can all reduce our risk.”

Sources of indoor pollution include:

Cooking (especially with gas hobs or burning food)
Household cleaning and air freshening products as well as personal care products
Wood-burning stoves and fireplaces
Outdoor pollution that enters through open windows and doors
Building materials and house renovations

Dr Daniels outlines four key areas to focus on:

1. Cooking: “Burning gas on the hob and scorched food releases harmful particles. If you can’t switch to an electric or induction hob, make sure your extractor fan works well. Cook on the back rings and open windows when you can.”

2. Sprays and household products: “Polishes, cleaning agents, and air fresheners reduce air quality. People with chronic lung conditions should limit use where possible.”

3. Outdoor air entering the home: “If you live near a road, try to keep street-facing windows closed during peak traffic times (between 7/9am and 4/6pm, Monday to Friday), when pollution levels are highest.”

4. Wood-burning stoves: “These significantly contribute to air pollution and are linked to lung cancer and heart disease. If you do use one, burn only dry, untreated wood at a high temperature. But better still — consider using them less often. Burn better, breathe better.”

Leading lung expert warms UK “sleepwalking” into indoor air pollution crisis