What Is Thirdhand Smoke?

thirdhand smoke

Story at-a-glance -

  • Despite decades of warnings, smoking continues to be the largest preventable cause of disease in the U.S., killing more than 480,000 each year and contributing $300 billion in direct medical care and lost productivity
  • You may be exposed to chemicals from cigarettes in smoke-free settings when toxins are deposited on furniture, carpeting and walls; called thirdhand smoke, you may inhale the chemicals after they once again become airborne
  • This invisible, toxic and sometimes odorless combination may be contributing to the rising number of people suffering lung cancer who have never smoked
  • The chemical residue may build, remaining in place for years, and is resistant to most normal cleaning methods, which means remediation may require replacement of furniture and carpeting, as well as cleaning walls and ceilings before repainting

By Dr. Mercola

Despite decades of education and warnings by the U.S. Surgeon General,1 smoking continues to be the "single largest preventable cause of cancer and disease in the United States."2 Cigarette smoking kills more than 480,000 people in the U.S. each year, contributing to $300 billion in direct medical care and lost productivity.

Health risks from smoking combustible cigarettes and e-cigarettes are not limited to your lungs. Some of the effects are immediate and others are clinically evident after several months or years of smoking. Nearly 30 percent of all cancer deaths in the U.S. are related to smoking and 80 percent of all lung cancer deaths can be attributed to smoking cigarettes.3

Many of these health conditions are the result of exposure to the 7,000 different chemicals found in combustible cigarettes, including nicotine, benzene and tar. Researchers recently found an alarming number of chemicals deposited from cigarette smoke in unexpected areas, increasing your risk of exposure to the same toxins responsible for cancers and diseases from cigarette smoking,4 even when you think you're in a smoke-free environment.

First-, Second- and Thirdhand Smoke

Prior to being smoked, an individual cigarette has nearly 600 ingredients.5 However, once burned, the combustion creates more than 7,000 chemicals, at least 70 of which are known to cause cancer and more that are poisonous.6 Smokers are exposed to primary or firsthand smoke as they inhale. Bystanders are exposed to secondhand smoke, the combination of smoke from the burning end of a cigarette and the exhalation from the smoker.

According to the U.S. Centers for Disease Control and Prevention (CDC),7 nearly 2.5 million adults have died from breathing secondhand smoke since 1964. In other words, there is no risk-free level of exposure to secondhand smoke. Health effects in children include middle ear infections, lower respiratory infections and sudden infant death syndrome. Adults exposed to secondhand smoke are at higher risk for stroke, coronary heart disease and reproductive problems.

Breathing secondhand smoke interferes with the normal functioning of your heart, blood and vascular system, which may increase your risk of having a heart attack.8 Even brief exposure may damage the endothelium and lining of the blood vessels, and trigger your platelets to become sticky. These changes may lead to a heart attack or stroke.

Thirdhand smoke is the combination of secondhand smoke sticking to surfaces and persisting in the environment long after the smoker has left,9 and includes nicotine.10 These tobacco-related gases and particles may become embedded in carpet, furniture, toys and blankets.

Unfortunately, the chemicals may also undergo transformation and accumulate before being released back into the air. While many are aware of the consequences of smoking cigarettes, and even exposure to secondhand smoke, the idea of exposure long after the smoker has left the room is relatively new, but gaining ground in the research community.

Thirdhand Smoke Exposes You to Hazardous Residue

Research into the potential dangers of thirdhand smoke has received coverage in the international media11 and scientific press, and court cases are appearing in which plaintiffs are citing dangers from exposure to thirdhand smoke.12 Cleveland Clinic pulmonologist Dr. Humberto Choi commented on the increasing number of lung cancer cases not directly related to first- or secondhand smoke, saying13 "we're looking at other causes for cancer aside from direct exposure." 

One study found exposure to thirdhand smoke may be causing damage to human DNA, increasing your risk of diseases.14 Airborne chemicals in a room or car may react with nitrous acid in the air, forming carcinogens. According to Choi,15 "It hasn't been proven that thirdhand smoke is correlated with any other conditions. And that will be very difficult to prove because we are all exposed to it no matter how hard we try to avoid it."

Georg E. Matt, psychology professor at San Diego State University, believes even in the absence of hard evidence thirdhand smoke may have long-term health effects. Nonsmokers and former smokers are already changing behavior by asking for nonsmoker rooms, apartments and cars, while real estate agents understand smoking negatively affects property values.16

Tobacco giant Philip Morris demonstrated their knowledge of the potential risks associated with thirdhand smoke in 1998 when they worked to change the public focus from potential health problems by designing answers to questions at their annual shareholder meeting using a marketing consultant and legally protected language, treating thirdhand smoke risks as merely rumor and blaming smoking restrictions on cigarette butt litter.17

Nonsmoking Is Not Necessarily Smoke-Free

While manufacturers would like you to believe dangers from thirdhand smoke are only rumors, animal studies suggest there may be an increased risk of lung cancer,18 immune damage,19 liver damage and diabetes.20 In the latest study, published in the journal Science Advances, researchers happened upon their findings by accident. Atmospheric chemist Peter DeCarlo, Ph.D., at Drexel University in Philadelphia, led a team intent on studying how indoor and outdoor air interact.

The researchers collected data from a college classroom off limits to smokers for years. The room contained 25 student desks, painted brick walls and a tile floor where chemical deposits were collected.21 The classroom received heating, ventilation and air conditioning from outdoor air. DeCarlo and colleagues compared the air inside the room to the air outside the building and found most of the aerosolized chemicals detected in the classroom originated from outside.22

In many cases, the concentrations of chemicals in the room were positively affected by the HVAC filtration system, and were lower in the indoor air. However, among four different organic aerosols identified by mass spectrometry, one was found mainly in the classroom at higher levels. This aerosol contained the residue of cigarette smoke, called thirdhand smoke. These results surprised the researchers who were testing areas off limits to smokers for decades, suggesting toxins are still present.23

The researchers collecting the data were interested in the movement of particles from outside to indoors. After careful examination and testing, they found 29 percent of the entire indoor aerosol mass contained thirdhand smoke chemicals.24 Subsequently, the team found these chemicals could attach to aerosolized particles and get back into the air, ultimately being transported into environments considered smoke-free. Michael Waring, Ph.D., co-author of the study, commented:25

"While many public areas have restriction on smoking, including distance from doorways, non-smoking buildings and even full smoking bans on campus for some universities, these smoking limitations often only serve to protect non-smoking populations from exposure to secondhand smoke. This study shows that thirdhand smoke, which we are realizing can be harmful to health as with secondhand smoke, is much more difficult to avoid."

Another study26 evaluated the presence of smoking chemicals, including nicotine, in a casino that banned smoking. The researchers found long-term smoking created deep thirdhand smoke reservoirs, persisting for months after the ban was instituted. While the ban improved air quality and reduced exposure to secondhand smoke, the reservoir of toxins continued to expose customers to low levels of toxic chemicals.

Children May Be at Greatest Risk

Unfortunately, children may suffer the greatest health hazard risks to thirdhand smoke and other environmental toxins. Childhood is a time of rapid growth, accompanied by changes in metabolic abilities and organ system functioning.27 These can dramatically modify the effects of exposure to environmental toxins. Their increased risk is the result of their increased exposure and vulnerability related to their physiological needs.28

Children's exposure to environmental toxins is insidious as they covertly enter the child's body through ingestion of household dust and mouthing areas of their environment, such as toys and furniture, where toxins may have been deposited. Children also consume more food and water per unit kilogram body weight and breathe more air. Immature organs are sensitive to external stimuli and their rapid growth increases the long-term accumulation of chemicals.29

Becoming Airborne Again

Researchers from Drexel began digging into the mechanism allowing thirdhand smoke to get indoors and become airborne again. Previous research had demonstrated as chemicals transition out of gas form they settle on any surface.30 However, they can concentrate in particles when the chemicals are in gas form and exposed to an acidic, liquid aerosol. This means they may be carried into smoke-free environments while waiting for the right conditions to transition into gas.

The researchers discovered a combination of conditions necessary for the particles to become aerosolized is actually pretty common indoors. They suggested the chemicals could return to a gas phase when exposed to specific chemicals often commonly found in buildings, such as ammonia. In fact, HVAC systems provide the necessary factors to spread toxic chemicals and the factors needed to become airborne again. The researchers wrote:

"The HVAC system not only serves to condition the aerosols to wet or dry states, but also to move air through a building zone. HVAC systems recirculate and disperse air throughout the multiple rooms of the zone served by the system. For this reason, a room located near a smoking area with smoke penetration or a room occupied by a smoker can effectively expose the other occupants served by the same HVAC system to third-hand smoke, even if they do not share space directly."

Research from Drexel only evaluated ventilated spaces, such as office buildings and classrooms. Waring explained31 concentrations are likely higher in residences, hotel rooms and rental cars where people had smoked and where there is less ventilation.

The researchers suggest the gravity of the situation indicated by the data raises important questions for further research about how you can limit exposure. It might be easy to recognize the presence of pollutants if you can see them or smell them, but this data is a reminder of how many odorless chemicals are in the environment.

Cleaning Residue Is Difficult

As chemicals and toxins from thirdhand smoke builds over time, it may remain for weeks, months or even years. This buildup is resistant to normal cleaning methods. Additionally, the toxins cannot air out of a room or car with fans or cleaned with vacuums.32 Unfortunately, the only solution is often to replace your carpet and thoroughly clean the walls before repainting them. Ventilation systems often need to be cleaned and furniture replaced.

It's expensive to completely eliminate thirdhand smoke from a room and eliminate exposure to future residents. The best way to manage the danger is to stop smoking. Your home represents a large portion of your exposure to risk related to the amount of time spent at home. If you're able to improve air quality in your own home, you go a long way toward reducing your potential risk over time.

Consider methods of improving air quality at home using some of the strategies outlined in my previous article, "The Air You Breathe Is More Polluted Than You Know." Researchers who studied the pollution effects of a smoking ban in a casino over time33 say you can accelerate positive health effects by remediating thirdhand smoke reservoirs, which include intensive cleaning and replacement of carpet, furniture and other materials.