What Is Thirdhand Smoke?

Thirdhand smoke is the nicotine and other chemicals from cigarettes that remain on surfaces well after someone has smoked. These residues can then be ingested, inhaled, or absorbed through the skin, potentially increasing the risk of certain cancers and other serious diseases. Some of these chemicals can also mix with common indoor pollutants to create toxins harmful to smokers and non-smokers alike.

Infants and small children are especially vulnerable to thirdhand smoke due to hand-to-mouth behaviors. Although there are ways to remove thirdhand smoke from the home, the only surefire way to protect yourself is to ban smoking where you live and to quit smoking if you do.

Routes of Exposure

Smoke does not dissipate in the air as some might suspect, and what's left behind is not without health concerns. That is why researchers at Massachusetts General Hospital in Boston coined the term thirdhand smoke in 2009.

Whereas secondhand smoke is what you inhale when someone else's smoke is circulating in the air, thirdhand smoke is the residue from smoke that settles and clings onto surfaces, objects, and fabrics in a room. This not only includes floors, walls, and counters but also clothing, furniture, toys, drapes, bedding, and carpets.

Unless the toxic chemicals are removed, they enter the body in one of three ways:

• Ingestion: Nicotine and other chemicals from cigarette smoke can enter the body if you touch a surface and bring your hand to your mouth. Children can also ingest these substances by putting contaminated objects in their mouths.
• Inhalation: Off-gassing is a term used to describe the release of residual contaminants back into the air, where they can be inhaled. This can occur while dusting, sweeping, shaking pillows, and turning on a fan or air conditioner.
• Absorption: In the same way that nicotine patches deliver nicotine through the skin, nicotine and other chemicals left behind after smoking can be absorbed through the skin. Because children have more delicate skin, the potential risk of this may be greater than for adults.

Fabrics pose a special concern in that the chemicals from thirdhand smoke are difficult to remove from fibers and weaves. A 2014 study published in PLoS ONE concluded than thirdhand smoke embedded in cotton terrycloth can potentially expose a toddler to seven times the amount of nicotine as passive smoking.

High humidity may reduce the risk by making the particles heavier and less likely to become off-gassed from surfaces. Low humidity may have the opposite effect.

Chemicals in Thirdhand Smoke

Of the multitude of chemicals found in thirdhand smoke, there are several that are known to be carcinogenic (cancer-causing). These include:

• Arsenic
• Benzene
• Butane
• Cadmium
• Cyanide
• Formaldehyde
• Lead
• Nicotine
• Polycyclic aromatic hydrocarbons
• Radioactive polonium-210

There is also evidence that thirdhand smoke can react with common indoor pollutants to form all new and potentially more serious toxins.

Among the concerns: nitrous oxide, which is created by fuel combustion and wastewater emission. When mixed with the chemicals in thirdhand smoke, nitrous oxide can create carcinogenic nitrosamines associated with lung cancer, liver cancer, oral cancer, stomach cancer, and esophageal cancer.

Furthermore, when mixed with ozone (also generated from fuel combustion), the chemicals in thirdhand smoke break down into ultra-fine particles, delivering formaldehyde and other carcinogenic compounds into the deeper airways of the lungs.

Dangers of Thirdhand Smoke

The research into thirdhand smoke is still relatively new and, at present, many of the proposed hazards are more theoretic than established.

With that said, there is mounting evidence of possible harms associated with thirdhand smoke:

• Cancers: A 2014 review in the journal Environment International concluded that cancer risks through exposure to the observed levels of TSNAs at an early life stage (1 to 6 years old) exceeded the upper-bound risk recommended by the U.S. Environmental Protection Agency in 77% of smokers' and 64% of non-smokers' homes.
• that this translates to one case of cancer for every 1,000 people.
• Coronary thrombosis: Mice exposed to thirdhand smoke exhibited increased hemostasis (blood coagulation) and an increased risk of blood clots. Investigators with the Western University of Health Sciences in Pomona, California concluded that this increases the risk of acute coronary thrombosis, which can obstruct blood flow to the heart and trigger a heart attack.
• Fatty liver disease: Animal studies have shown that thirdhand smoke stimulates the accumulation of fat in liver cells, increasing the risk of metabolic dysfunction-associated steatotic liver disease (MASLD, formerly known as NAFLD). MASLD is not only a precursor to cirrhosis and liver cancer but also a potential contributor to cardiovascular disease.
• Hyperactivity: Secondhand smoke is linked to hyperactivity in children, and there is evidence that the same can occur with thirdhand smoke. This is likely caused by nicotine that acts as both a stimulant and depressant in the central nervous system.
• Impaired wound healing: Thirdhand smoke was found to interfere with wound elasticity—that is, how rapidly a wound heals and how extensively scar tissue develops.
• Insulin resistance: Studies in mice have found that the oxidative damage caused by thirdhand smoke reduces insulin receptors on pancreatic cells and increases the risk of insulin resistance (a precursor to type 2 diabetes).
• Pulmonary fibrosis: Animal studies suggest that off-gassed thirdhand smoke can affect the production of collagen in the smaller airways (bronchioles) and air sacs (alveoli) of the lungs, leading to the thickening and scarring of tissues (pulmonary fibrosis). This can further complicate breathing problems in people with asthma, chronic obstructive pulmonary disease (COPD), or cystic fibrosis. It might even affect normal lung development in children.

As concerning as these risks are on paper, it is still unknown how much thirdhand smoke contributes to the onset of disease. Some researchers express doubt, for example, that nitrosamines can be readily absorbed or ingested in a way that can directly link them to cancer or other illnesses.

It is simply too early to say; further research is needed, particularly in relation to the findings of animal studies and their application in humans.

Still, any risk of thirdhand smoke only adds to the risks of secondhand smoke in smoking households. And unlike secondhand smoke, the risk of thirdhand smoke can increase over time as more and more toxins are deposited on surfaces.

Avoiding Thirdhand Smoke

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

Even if smoking is stopped, don't expect the problem to spontaneously disappear. Research from the University of California Riverside found that thirdhand smoke can persist on surfaces, especially fabrics and furniture, for 19 months. Thirdhand smoke can even persist after a room is painted and re-carpeted.

If you think you are being exposed to thirdhand smoke, there are things that you can do to protect yourself and your family:

• Do not allow smoking inside your home or car.
• Do not allow smoking near your family or pets.
• Educate your family and friends about thirdhand smoke, and your related concerns, so that they understand the rules of the house and why you've set them.
• Advise caretakers of your no-smoking policy. If hiring a caretaker, be sure to include "non-smoker" in the job posting. (In some states, it is tricky and potentially illegal to ask a potential employee if they smoke.)
• If you’ve been in a house with smokers, shower thoroughly with soap and warm water even if they weren't smoking in front of you. The same applies to pets. Also clean any toys and clothes exposed to smoke with detergent and hot water.

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 cleanser to remove nicotine, it must be acidic. But most soaps are alkaline and fail to remove nicotine even from smooth surfaces.

On the flip side, acidic solutions like vinegar can remove thirdhand smoke from surfaces, but this option is not always practical as it can damage granite, marble, limestone, onyx, travertine, and grout, as well as leave behind a powerful smell.

The non-profit American Nonsmoker's Right Foundation recommends that property owners and managers take the following measures before new tenants move in:

• Thoroughly wash walls and ceilings with detergent and hot water.
• Repaint walls with two or three coats of paint but only after the walls have been cleaned. Nicotine can still seep through three layers of paint.
• Remove carpeting and padding, washing the floors thoroughly before re-carpeting.
• Remove wallpaper. Wash the walls thoroughly before repapering or painting.
• Replace all curtains, windows, and blinds.
• Clean out ventilation ducts, and replace filters in the air conditioner and heating systems.

A Word From Verywell

Thirdhand smoke is a relatively new concept but one that should be of concern, especially to parents. As there is no such thing as a "safe" amount of secondhand smoke, no amount of thirdhand smoke should be considered "safe" if you have a newborn or infant (or are living with a severe respiratory disease like COPD).

By instating a smoking ban in the home, you can significantly reduce your exposure to thirdhand smoke. If someone in your home does smoke, restricting smoking to outdoor spaces may not be enough. The only guaranteed solution is for them to quit smoking, ideally under the care of a doctor with approved smoking cessation aids.