Indoor Smoking Bans May Not Be 100% Effective

Third-hand smoke may be lurking on clothing, countertops and more

Researchers at Drexel University in Philadelphia looked at how particles from outside air get inside and found a “chemical signature” that didn’t exist outdoors – which they identified as third-hand smoke – the residue that can be carried on clothing and hair or left behind on couches and counters long after cigarette smoke has cleared.

Those particles can reactivate when they come into contact with the natural ammonia emitted from the human body. Temperature and humidity can also be factors.

The researchers tested the air in an unoccupied classroom where smoking had not been allowed in decades. They found that 29 per cent of the indoor aerosol mass contained third-hand smoke particles.

Particulate matter in the air is just a small fraction of what we breathe in. What’s worrisome is the concentration of contamination. The researchers suggest being in a room contaminated with third-hand smoke during an average workday is the equivalent of being in a room filled with second-hand smoke for about five minutes.


The health risks of this so-called third-hand smoke are becoming more apparent. A Stanford University study using laboratory mice found skin contact with the compounds in third-hand smoke increased the severity of asthma symptoms. It is also known to increase the risk of lung cancer in mice.

Young children are particularly vulnerable since they are more likely to be crawling on contaminated carpets or ingesting the residue when they put their hands in their mouths.

Concentrations of third-hand smoke particles are likely higher in residences, hotel rooms, or rental cars where people have previously smoked.

banner image via Drexel University