Why Thirdhand Smoke is So Dangerous

What is Third-Hand Smoke?

close up of lit cigarette and cigarette ash
Daniel Grill/Getty Images

Thirdhand smoke (THS) is a term originally coined by doctors at Massachusetts General Hospital for Children. Meant to describe dangers specifically associated with residual toxins left behind on surfaces once firsthand and secondhand smoke have cleared out of a room, we now understand more about the composition of THS that lingers in the air, as well.

What is Thirdhand Smoke?

Have you ever stood in a check-out line and known there was a smoker nearby, even though no one was smoking anywhere close?

Or maybe you walked into a room thick with the unmistakable smell of stale cigarette smoke, even though there was no visible smoke in the room?

Or, if someone smokes in your house or car, how about that yellow gunk you clean off the windows?

These are all examples of what is known as THS, a noxious mix of gases and small particles that remain in the air for hours after a cigarette is smoked, and are deposited on every surface they come into contact with.

From air, to hair, clothing, bedding, furniture, carpets, table surfaces and toys, nothing is exempt from contamination if it's in a room or other closed environment (like a vehicle) where cigarettes were smoked.  

First, Second and Thirdhand Smoke

So, what is the difference between firsthand smoke, secondhand smoke and thirdhand smoke?

Firsthand smoke is cigarette smoke that a smoker draws into his or her lungs when inhaling from a lit cigarette.

Secondhand smoke is a combination of exhaled firsthand smoke and the smoke wafting into the air from the end of a burning cigarette.

Thirdhand smoke can be broken down into three distinct parts:

1. Gases and small particles that are suspended for hours in the air of rooms or other closed spaces (aged secondhand smoke).

2. Tiny solid particles that settle and stick to surfaces of an enclosed area.

3. Toxins on surfaces and in the air that combine with other common indoor pollutants, creating new chemical compounds or more dangerous forms of chemicals in the process.

Thirdhand Smoke In The Air

Scientists have discovered that aging secondhand smoke hanging in the air of an enclosed space changes over time in unexpected ways.

While most of the solid particles in THS fall to surfaces within 20 minutes, some solid matter does remain in the air and can be inhaled into the lungs.

Additionally, the levels of some chemicals in secondhand smoke actually increase for a time as the smoke transitions to THS, making breathable air in a room more dangerous.  

Three toxic chemicals of this type that have been identified are acrolein, methacrolein and acrylonitrile.  The first two are respiratory and eye irritants, and the third, a highly flammable carcinogenic compound.

Thirdhand Smoke on Surfaces

Nicotine and other toxins from cigarette smoke coat everything it comes in contact with. And worse, some of those chemicals are transformed when they come into contact with other common indoor pollutants. For instance, when nicotine reacts with nitrous acid on indoor surfaces, it creates TSNAs, a group of highly carcinogenic chemicals.

Chemicals from THS also stay in the environment for a long time.  Research has shown that rooms that were smoked in retain THS in dust and on surfaces long after smoking has ceased.  It even persists after cleaning and repainting.  

Chemical Fumes That Rise From Surfaces

Researchers have learned that some of THS toxins parked on surfaces can off-gas, meaning that chemical fumes are released back into the air from the solid particles in that residue.

Other Dangers Related to Thirdhand Smoke 

Scientists have learned that when ozone mixes with residual nicotine in the air and on surfaces, it transforms into ultra-fine particles that can be inhaled deep into the lungs.

 These particles may be difficult for the body to expel and could cause additional breathing problems for asthma sufferers.

Thirdhand Smoke Risks for Children

The chemical fallout that settles on surfaces from the gases and small particles in cigarette smoke isn't good for anyone to be exposed to, but it's especially harmful for small children.   They are much more likely to ingest these invisible toxins when touching furniture, floors and toys, because they put their fingers (and toys, etc) in their mouths often.

It should also be noted that THS in the air is a greater risk for babies and young children too,  because their respiratory rate is faster.  This causes them to inhale more toxins in the same amount of time as someone who is older with a slower rate of breathing.

The Bottom Line

We've known for a long time that cigarette smoke is dangerous air to breathe. Now we also know that secondhand smoke lingers, settles and even transforms into other dangerous chemicals known as thirdhand smoke.

It is important for your health and those you care about to avoid indoor areas where smoking is allowed.  If you have smokers in your family, set a strict boundary about smoking outside.

Other Chemicals in Cigarettes

Researchers have identified upwards of 7000 different chemical compounds that are present in cigarette smoke, including 250 poisonous gases, 70 carcinogens and several heavy, toxic metals.

Do your part to insure that children don't suffer the health hazards posed by cigarette smoking. Ban smoking in your home and car, and if you smoke, quit now


Inhalable Constituents of Thirdhand Tobacco Smoke: Chemical Characterization and Health Impact Considerations. Environmental Science and Technology. Accessed September, 2015.

Formation of carcinogens indoors by surface-mediated reactions of nicotine with nitrous acid, leading to potential thirdhand smoke hazards. National Institutes of Health. U.S. National Library of Medicine. Accessed September, 2015.

Third-Hand Smoke: Another Reason to Quit Smoking. 29 December, 2008. EurekAlert - American Associateion for the Advancement of Science (AAAS).

Thirdhand Smoke Identified as Potent, Enduring Carcinogen. Wiley Online Library. Accessed September, 2015.

When smokers move out and non-smokers move in: residential thirdhand smoke pollution and exposure.. National Institutes of Health. U.S. National Library of Medicine. Accessed September, 2015.

Berkeley study shows ozone and nicotine a bad combination for asthma. University of California, Berkeley. Accessed September, 2015.

Thirdhand Smoke: Toxic Airborne Pollutants Linger Long After the Smoke Clears. University of California, Berkeley. Accessed September, 2015.