Thirdhand smoke: a toxic time-release capsule

A new study has investigated the threat of ‘thirdhand smoke’ highlighting the fact that the dangers of indoor smoking persist long after the cigarette is put out.

While secondhand smoke is directly inhaled, thirdhand smoke (THS) is the toxic chemical residue that clings to walls, furniture, carpets and fabrics. This sticky residue acts as a persistent, low-level source of air pollution that can re-emit harmful compounds for hours or even days.

The new research shows that this pollution isn’t static but evolves over time.

Professor Yele Sun, the study’s corresponding author explains: ‘The key takeaway is that thirdhand smoke is not a static stain; it’s an active and ongoing source of pollution in a room. The smoking session might end, but the release of hazardous compounds continues, exposing people to low levels of toxins long after the fact. This turns our homes into environments of chronic, low-dose exposure.’

Using advanced air monitoring technology, Professor Sun’s team tracked the real-time chemistry of thirdhand smoke in an indoor environment. They found that while secondhand smoke particles dissipate, thirdhand smoke aerosols maintain a stable, measurable presence in the air at low concentrations (1–2 μg m⁻³). Furthermore, the chemical signature of these lingering particles changes, becoming notably enriched with nitrogen-containing compounds over time, which may alter their toxicity.

The research found that porous materials such as wool sweaters, carpets and upholstery soak up tobacco molecules deep into their fibers. This deep penetration creates a ‘reservoir effect,’ causing a slow, prolonged release of pollutants that is resistant to simply opening a window.

Thirdhand smoke acts like a toxic time-release capsule, emitting chemicals in three stages, starting with a quick burst of gases, then a hours-long release of nicotine compounds and finally a slow, days-long trickle of other pollutants. This means a single smoking session creates a continuous, low-level source of harmful air pollution long after the cigarette is gone.

The full research can be accessed here.

Photo: Sara Kurfeß / Unsloash