A Chinese study reveals hidden dangers of third-hand smoke in indoor spaces

A new Chinese study, published in the journal Building and Environment, highlights a persistent and evolving threat to indoor air quality linked to what is known as “third-hand smoke,” or third-degree passive smoking.

Conducted by researchers from the Institute of Atmospheric Physics of the Chinese Academy of Sciences, the study explains that third-hand smoke does not disappear once smoking has stopped.

 Instead, it remains trapped in enclosed spaces and undergoes chemical transformations over time, becoming a permanent source of pollution.

Third-hand smoke refers to the residues of toxic substances emitted from tobacco smoke that settle on indoor surfaces such as walls, furniture, carpets, and curtains. Unlike second-hand smoke, which is inhaled directly from the surrounding air, this type of pollution settles and accumulates inside homes and is then gradually released back into the ambient air.

The research findings show that third-hand smoke represents a dynamic source of pollution, as it continuously re-emits fine particles and gases into the air while undergoing chemical changes that increase its harmfulness over time. Measurements also revealed that this smoke persists at low but stable levels indoors, unlike second-hand smoke, which dissipates relatively quickly.

Researchers observed that the chemical composition of particles emitted from third-hand smoke becomes increasingly nitrogen-rich over time, promoting the formation of compounds that are more harmful to health.

The study also reveals that porous household materials, such as wool carpets and textiles, act as reservoirs that absorb these toxic substances and then slowly release them.

 This makes the pollution resistant to conventional ventilation and prolongs its presence for hours or even days after just a single cigarette has been smoked.

Commenting on the study’s results, Professor Sun Yeh Le of the Institute of Atmospheric Physics emphasized that these findings constitute important scientific evidence to support public health policies. He stressed the need to include third-hand smoke in tobacco control strategies and indoor air quality standards.

He added that the research provides new chemical indicators that make it possible to detect this long-neglected form of pollution, warning that it represents a silent and persistent health challenge that calls for greater awareness and strengthened preventive measures to ensure safer indoor environments.