Thirdhand Smoke: Exposure Routes, Risks, and Dangers

Exposure may be particularly dangerous for infants and children

Thirdhand smoke, defined as the particles and gases left behind from tobacco, is now considered to be an additional danger to non-smokers in addition to passive smoking (exposure to secondhand smoke). Toxins such as nicotine, cyanide, lead, polycyclic aromatic hydrocarbons, and more may be present on surfaces where a person has smoked long after the cigarette is extinguished. Recent studies suggest that those who are at greatest risk are young children. We will look at common exposure routes, specific toxins, how to avoid thirdhand smoke, and how to remove it when possible.

Exposure Routes

It might seem obvious that substances left over after a cigarette is put out could be dangerous. After all, the list of additives in cigarettes is frankly terrifying. But there is more than one mechanism by which third-hand smoke causes problems.

Chemicals on Surfaces

The first route is easiest to understand. Chemicals that are left over after smoking land on any surface in an area where smoking has taken place. Studies have found that of chemicals in third-hand smoke, 11 are carcinogens (substances capable of causing cancer). A few of the chemicals that have been found on surfaces after smoking include nicotine, cyanide, radioactive polonium-210, lead, arsenic, polycyclic aromatic hydrocarbons, and butane.


A second way that toxins can be of concern with third-hand smoke is through a process called “off-gassing." Off-gassing occurs when substances from smoke that have been deposited on surfaces (such as nicotine) are released back into the air as gases. Through this process, tobacco residue that has built up on surfaces continues to emit toxins long after smoking has occurred.

Interaction With the Environment

In addition to toxic chemicals that are present on surfaces or released into the air, a third route of exposure is when new toxins are created by the interaction of substances in thirdhand smoke with other chemicals present in the environment. Two examples of interactions that have been documented include:

  • When thirdhand smoke reacts with nitrous oxide (for example from gas appliances or car engines) in the air creating carcinogens known as nitrosamines.
  • When volatile organic compounds (VOCs) in thirdhand smoke react with ozone in the air to create formaldehyde among other chemicals.

How Exposure Occurs

There are at least three ways in which people may be exposed to the toxins in thirdhand smoke.

  • Inhalation: Particles found in thirdhand smoke may be directly inhaled when the surface they are on is disturbed. Off-gassing also gives rise to substances that can be inhaled.
  • Ingestion: Particles that land on food or fingers may be ingested, but particles on any other surface that is touched and then placed in the mouth (especially in the case of exploring toddlers) may result in ingestion.
  • Skin absorption: Absorption of substances through the skin may seem less obvious at first. Yet, in this era in which we have patches for nicotine, hormones, and other medications, it's clear that our skin is not a solid barrier to substances in our environment.

It is thought that children are likely at greater risk of thirdhand smoke exposure than adults. The carcinogens in dust tend to settle to the floor—where children are sitting and playing. Children are also more likely to put their fingers to their mouths after touching surfaces contaminated by thirdhand smoke

A high humidity level appears to be protective to some degree, so people in regions where humidity is low may be at a greater risk of exposure.

Ozone in the air also varies. For example, the reaction of volatile organic hydrocarbons in thirdhand smoke with ozone in the air would be of greater concern in an airplane, than say a vehicle on the ground.

Dangers of Thirdhand Smoke

It is too early since the discovery of third-hand smoke to accurately quantify the risks. Considering that the U.S. Surgeon General states that there is no risk-free level of secondhand smoke, and since thirdhand smoke contains many of the same toxins, it seems wise to say that any exposure to third-hand smoke should be minimized as well.

Unlike secondhand smoke, the risk of third-hand smoke can actually increase over time as more toxins are deposited on surfaces in a home or vehicle.

While there are concerns, it's important to note that much of we know at the current time comes from studies done in the lab or with animals. While effects seen in a laboratory dish or another species do not necessarily predict what will occur in humans, it's a helpful starting point for determining the role of thirdhand smoke in health.

Some of the concern also relates to indirect evidence, knowing about chemicals linked to cancers found in thirdhand smoke, but not knowing the role that the presence of these chemicals in thirdhand plays directly in cancer.

Researchers have just begun to evaluate possible dangers, but findings thus far include:

Impaired Wound Healing

Thirdhand smoke was found to interfere with the healing of wounds, and also "wound elasticity"—in other words, how rapidly a wound will heal and what kind of scar will be formed.

Insulin Resistance

Studies in mice have found that thirdhand smoke causes molecular changes in cells (via oxidative stress) which leads to insulin resistance (simplistically, the precursor to diabetes).


There is early evidence that thirdhand smoke may raise the risk of cancer. Nitrosamines—chemicals found in thirdhand smoke—above the limits recommended by the Environmental Protection Agency for children aged 1 to 6 are found in 77% of homes which have smokers. This is thought to translate into 1 case of cancer for every 1000 people. It's important to note, however, that this research is still very young, and most chemicals in thirdhand smoke have not yet been studied in this manner.

Fatty Liver Disease

Thirdhand smoke exposure in mice can result in fatty liver disease, which in turn may lead to cirrhosis and heart disease.

Induction of Fibrosis

Thirdhand smoke exposure may result in biological changes in cells that predispose to fibrosis, which raises concern that it may play a role in COPD and asthma.

Platelet Issues

Changes in how platelets combine due to thirdhand smoke raises concern that exposure may increase the risk of blood clots and heart disease.


Thirdhand smoke exposure in mice results in hyperactivity, and there is concern that prolonged exposure in children could result in more serious neurological conditions.

How to Avoid Thirdhand Smoke

The best way to avoid thirdhand smoke is to have a zero tolerance policy for smoking in your home and your vehicle. Unlike secondhand smoke, ventilation does little to remove thirdhand smoke, and once it is there, you may not even know it.

Unlike the old adage; time doesn’t heal when it comes to thirdhand smoke. The fact that it lingers on is evident if you’ve ever stayed in a hotel that once-upon-a-time allowed smoking. Even if it’s been smoke-free for a decade, those with bloodhound noses can still catch whiffs of days when the rules were different. And studies have confirmed this as well. Swabs taken from homes in which smoking has taken place still have measurable levels of thirdhand smoke after being left vacant for 2 months.

If you still anticipate being exposed to thirdhand smoke, here are a few tips:

  • Shower, washing your hair and skin if you’ve been exposed
  • When possible, clean surfaces and materials exposed to smoke with vinegar. Keep in mind that this is not always practical, and may permanently stain and discolor certain fabrics and surfaces.
  • If you choose to allow smoking in your home, open windows and try to discourage smoking in rooms that have carpeting. That said, with central heating or central air, the contaminants will still be circulated throughout your home.
  • Educate your friends and family. Studies that have looked at the beliefs of people surrounding smoking have found that if smokers realize that their smoking (via secondhand or thirdhand smoke) affects others, they are more likely to enforce a household smoking ban.

How to Remove Thirdhand Smoke

Removing thirdhand smoke is tougher than it sounds. Washing or dry cleaning alone may not cut it. In order for a cleaner to remove nicotine, it must be acidic. Yet most soaps are alkaline (the opposite of acidic) and fail to remove nicotine even from smooth surfaces. Using an acidic solution such as vinegar may remove it from surfaces such as marble, but is not always practical. Most people don’t want their comfy couches smelling like vinegar. For the same reason, removing thirdhand smoke from carpeting is virtually impossible. If you wish to remove thirdhand smoke from your home, replacing carpeting, though pricey, is likely the best option.

Quitting smoking is the best way to avoid third-hand smoke.

A Word From Verywell

The concern over thirdhand smoke may lead to groans about yet another thing causing cancer. Yet we know that firsthand and secondhand exposure is harmful, so measures to avoid smoke exposure are wise. Removing thirdhand smoke that lingers may be of more concern to parents with young children.

It is clear that there are carcinogens in thirdhand smoke and that these persist for a long period of time after a cigarette is extinguished, sometimes indefinitely. Since the research is new, it's not a bad idea to practice caution until more is known. After all, avoiding thirdhand smoke and taking measures to remove it when possible may be aesthetically pleasing as well as you clean up the environment where you live.

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  2. Adhami N, Starck S, Flores C, Martins Green M. A Health Threat to Bystanders Living in the Homes of Smokers: How Smoke Toxins Deposited on Surfaces Can Cause Insulin Resistance. PLoS One. 2016. 11(3):e0149510. doi:10.1371/journal.pone.0149510

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