In 2006, the U.S. Surgeon General reported that “the scientific evidence indicates there is no risk-free level of exposure to secondhand [tobacco] smoke.” At that time, over 50,000 deaths per year were attributed to secondhand tobacco smoke alone. Although more studies are needed on cannabis (marijuana) secondhand and thirdhand smoke, some data already available shows that kids may be at risk. There are many similarities between tobacco and cannabis smoke, so we can infer health effects from exposure to cannabis smoke from the established evidence on tobacco smoke. This post covers what we do and do not yet know about secondhand and thirdhand smoke from cannabis.
What is secondhand and thirdhand smoke?
Secondhand smoke (SHS) is smoke coming off the burning end of a tobacco cigarette, cannabis joint or other smoking device, plus the mainstream smoke that comes from the smoker’s end. SHS contains thousands of chemicals including ammonia, carbon monoxide, formaldehyde, hydrogen cyanide, polyaromatic hydrocarbons and many other toxins.
Thirdhand smoke, also known as “aged” or “residual” smoke, is the secondhand smoke particles that stick around in air, dust and on surfaces for days to months. These particles can be transformed into new chemicals or re-emitted into the air. The presence of thirdhand smoke is sometimes obvious, such as when you smell it on a smoker’s clothing, but it can also be hidden in the carpeting or dust in the home.
Cannabis vs. tobacco, isn’t the smoke different?
Cannabis and tobacco smoke are very similar in that they both are mostly composed of plant biomass. They obviously differ in their active compounds: cannabinoids/THC (tetrahydrocannabinol) and nicotine. However, the secondhand smoke from the burning biomass of both cannabis and tobacco has been shown to cause cancer. Of the many proven side effects of nicotine, the most concerning is its cardiovascular damage. The secondhand smoke from cannabinoids are especially worrisome because they affect the developing brains of children and adolescents. Early-life exposure is associated with lower volume of brain grey matter and poorer performance on cognitive tests.
What are the health effects of thirdhand smoke?
Most of the current studies on thirdhand smoke are related to tobacco. Tobacco thirdhand smoke contains carcinogens and toxins that damage DNA, affect cognitive and respiratory function, and hinder wound-healing. Some evidence suggests that these chemicals can build up to measurable amounts in the body. The blood test for tobacco smoke (known as cotinine) has been shown to be significantly higher in nonsmokers who live in homes of previous smokers than those in homes without previous smokers. This shows that tobacco smoke particles that have remained in the home can be breathed in or swallowed by non-smokers. It is safe to assume that the same may be true of cannabis smoke. Thirdhand smoke particles probably remain on clothing, furniture, and house dust where children can breathe them in or swallow them.
Children and infants are the most susceptible to the health effects of thirdhand smoke. First, they spend more time near dust and are more likely to insert non-food items into their mouths, swallowing the attached dust particles. Second, they breathe much faster than adults, so they’re taking in more particles in the air. Lastly, their developing bodies and especially their brains are more susceptible to the harmful effects of chemicals, such as those in thirdhand smoke.
Is vaping safer?
Possibly. Vaporized smoke (tobacco or cannabis) out of electronic devices at low temperatures may be less toxic because at high temperatures a more toxic smoke is produced (e.g. formaldehyde formation occurs at the higher temperatures). Also, the electronic devices produce significantly less smoke, and therefore may produce less thirdhand smoke particles. Vaping may also include the use of vaping oils and other compounds derived from plants which consist of less biomass, so there may be a lower concentration of biomass toxins. But vaping oils often contain other liquid compounds not seen in the dry plants, whose health effects have not been studied. And studies suggest that toxin-containing dust is elevated in the homes of people using vaporizing. Currently, there is very little regulation of and evidence for the safety of these vaping compounds. Many of the added chemicals have little evidence proving their safety, while others have been shown to cause DNA mutations.
Why is this a Public Health concern?
Protecting people from involuntary smoke exposure (e.g. a non-smoker in the home of a previous smoker), and the negative health consequences is a public health issue. In recent years, complaints of smell, eye irritation and respiratory distress have led to smoking bans in many private sectors (e.g. rental cars, hotels, etc).
We need coordinated efforts to develop, reinforce and strengthen norms toward establishing and maintaining smoke-free environments. Voluntary no-smoking policies have been shown to have positive outcomes. Not surprisingly, children living in homes with no-smoking policies have six times lower markers for smoke exposure (via cotinine measurements). The American Academy of Pediatrics offers help to quit smoking. Click here for more information.
How do I get rid of thirdhand smoke in my home?
Remediating a home with previous smoke is not the best solution. Although replacing carpeting and repainting has been proposed as a means to rid the home of thirdhand smoke particles, evidence has shown continued elevation of toxins in dust of these homes afterwards. The scientific community’s concern about thirdhand smoke has lead the U.S. Department of Housing and Urban Development to invest in developing cleaning techniques that effectively remove thirdhand smoke. In the meantime, preventing smokers and their smoke from entering your home is an effective way to avoid exposure.
The Tobacco-Related Disease Research Program has focused on thirdhand smoke research since 2010 and continues to provide quality studies.
The lack of evidence for adverse effect from thirdhand cannabis smoke does not make it harmless. Although more studies are needed on thirdhand smoke from both tobacco and cannabis, there is enough evidence to warrant caution and avoidance of thirdhand smoke. As cannabis is becoming increasingly legal and available across the United States, long-term and more robust secondhand and thirdhand smoke studies are not only necessary, but more feasible.
April 2017. This blog post was written by Melissa Pavelack, Medical Student at the Chicago College of Osteopathic Medicine and edited by Dr. Susan Buchanan.
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