Outdoor air pollution is already being seen as a major health threat, but new research is sounding an alarm much closer to home. The “safe” environment people retreat into — their houses, schools and workplaces — may itself be quietly exposing them to a dangerous mix of harmful chemicals, according to researchers.
In their study published in the journal ‘New Contaminants’, they warn that indoor dust, air and everyday household products are increasingly contaminated with a range of “new contaminants” that are poorly regulated and rarely monitored. These substances, researchers say in their study “New contaminants in indoor environments: occurrence, transformation, and health risks,” could raise the long-term risk of heart disease, cancer, hormonal disorders and developmental problems, even though people are largely unaware of their presence.
This warning is especially serious because people now spend nearly 90 per cent of their time indoors. Yet pollution research, regulations and public awareness continue to focus overwhelmingly on outdoor air, leaving indoor environments largely unchecked.
Modern indoor spaces contain a complex cocktail of chemicals released from furniture, building materials, carpets, paints, electronics, cosmetics, cleaning products and plastics. Unlike outdoor pollution, which can disperse, indoor pollutants often linger. Energy-efficient buildings are more airtight, trapping contaminants and increasing long-term exposure.
“In many buildings, indoor pollution can be more severe than what we measure outside,” said Wei Du of Kunming University of Science and Technology, the corresponding author of the study. “That is particularly worrying for children and older adults, who spend most of their time inside these environments.”
The danger is often invisible. Many of these pollutants have no strong smell or immediate symptoms, allowing exposure to continue unnoticed for years.
Unlike familiar indoor hazards such as carbon monoxide or formaldehyde, the contaminants highlighted in the study are newer and less understood. They include persistent organic pollutants, endocrine-disrupting chemicals, antibiotics and microplastics.
These substances can be released from common items such as shampoos, sunscreens, toys, plastic containers, electronics, office materials and childcare products. Once indoors, they enter the body through breathing contaminated air, ingesting dust or through skin contact.
Alarmingly, researchers have already detected these chemicals in human blood, urine, breast milk and even bone marrow.
Dust and surfaces can act like tiny chemical reactors, where pollutants interact with indoor light, ozone and oxidants to form new compounds — sometimes more toxic than the original substances.
For instance, flame retardants or fragrance chemicals can transform into derivatives with stronger neurotoxic or hormone-disrupting effects. This makes indoor exposure harder to assess and far less predictable than outdoor pollution.
The authors caution that relying on outdoor air studies to assess indoor risks may severely underestimate the true health impact.
What is more cause of worry is that despite mounting evidence, indoor air standards remain weak or nonexistent for many of these emerging contaminants. The authors have urged governments and regulators to treat indoor pollution as a serious public health issue, not a secondary concern.
They have also called for systematic monitoring of indoor environments — including homes, schools, hospitals and offices — to build data that can guide regulation. Advanced measurements, research into chemical transformations and targeted health studies are urgently needed.
“Finally, toxicological and cellular studies should be conducted to evaluate the health risks of new contaminants, providing a scientific foundation for their regulation and the development of indoor environmental standards.”
Protecting human health increasingly means looking inward, said co-author Bo Pan. “The places where we live, learn and work must be recognised as a critical frontier for pollution control.”
