Second Hand Cannabis Smoke

Fine Particulate Matter Exposure From Secondhand Cannabis Bong Smoking

March 30, 2022


The PM2.5 concentrations generated in a home during social cannabis bong smoking to which a nonsmoking resident might be exposed were greatly increased compared with background levels, and PM2.5 decayed only gradually after smoking ceased. After 15 minutes of smoking, mean PM2.5 (570 μg/m3) (Figure) was more than twice the US Environmental Protection Agency (EPA) hazardous air quality threshold (>250 μg/m3). If one assumes the exposure concentrations were at the mean levels observed, a single home smoking session with no other exposures would generate an estimated mean daily concentration (200 μg/m3) that greatly exceeds the average in cigarette-smoking homes (44 μg/m3), nonsmoking homes (15 μg/m3), and the US EPA daily standard (35 μg/m3).3 A strength of this study is that measurements were made during actual social bong smoking sessions without artificial constraints. Limitations include that cannabis smoking was not directly observed.

This cohort study suggests that, contrary to popular beliefs, bong smoking is not safe. Decades ago, many people thought SHTS presented no health risk to nonsmokers. Scientific research since then changed this perception and led to smoke-free environments.3 Incorrect beliefs about SHCS safety promote indoor cannabis smoking.1,2 Nonsmokers are exposed to even higher concentrations of SHCS materials during “hot-boxing,” the popular practice in which cannabis smokers produce high volumes of smoke in an enclosed environment. This study’s findings suggest SHCS in the home is not safe and that public perceptions of SHCS safety must be addressed.

An emerging allergen: Cannabis sativa allergy in a climate of recent legalization

6 June 2020

The legalization and accessibility of Cannabis sativa in Canada has created a renewed interest in the health implications of its use, including allergic and immunologic consequences. This brief review has highlighted the diversity of sensitization routes and reactions to the plant, emphasizing the heterogenous presentation of Cannabis allergy. In addition, this article has underscored the fledgling nature of available testing and treatment options for C. sativa allergy. There have been recent, exciting advancements in isolation of culprit allergens and clinical testing, although these are not yet applicable to general office use. At the moment, there are existing practical suggestions for diagnosing and treating C. sativa allergy, which will hopefully evolve in the coming years as Can s 3 preparations and immunotherapy schedules mature and become commercially available. However, currently, a detailed allergy history with adjunct hemp sIgE testing are the cornerstones of diagnosis, and avoidance (in combination with standard symptomatic treatment) is the mainstay of treatment

Cannabis allergy: what the clinician needs to know in 2019

  • Cannabis allergy can elicit a variety of symptoms from mild rhinoconjunctivitis to life-threatening anaphylaxis;
  • Crude extract-based diagnostics show a very high sensitivity albeit a low specificity;
  • Can s 3, the nsLTP of Cannabis sativa, is a major allergen with Can s 3 based diagnostics showing the highest performance;
  • Reports suggest that symptoms can occur after smoking, cutaneous contact but also ingestion of spacecake, cannabis tea, oil or hemp seeds;
  • A significant number of patients even report symptoms on indirect smoke exposure or cutaneous contact;
  • Cannabis allergy has been described following both recreational use and occupational cannabis exposure.

Surface Detection of THC Attributable to Vaporizer Use in the Indoor Environment

2019, December 09

We showed that in a room in which cannabis was administered by vaporization surfaces tested positive for THC at quantifiable levels. This study represents a first step in understanding how side-stream cannabis vapor deposits in the environment and may result in tertiary exposure to users and bystanders.

Health effects of exposure to second- and third-hand marijuana smoke: a systematic review

 2017 Nov 24


Tetrahydrocannabinol metabolites are retained in the body upward of 4 hours, and people report the experience of psychoactive effects after exposure to second-hand smoke. On a molecular level, marijuana smoke has chemical components similar to those of tobacco smoke, although they are present in different amounts. Although this provides support for the biological plausibility of the relation between exposure to second-hand marijuana smoke and negative health outcomes, there is a gap in the literature in this area. If exposure to second-hand marijuana smoke has similar health risks as direct marijuana use, it may be associated with conditions such as respiratory and cardiac disease as well as mental illness. However, high-quality research on the long- and short-term health effects of exposure to second-hand marijuana smoke are required to confirm these possible risks. Given the current state of knowledge, coherent policy approaches to exposure to smoke of any kind may result in the most effective harm-reduction policy.

Measuring indoor fine particle concentrations, emission rates, and decay rates from cannabis use in a residence

 April 2021,


-60 experiments comparing indoor PM2.5 from secondhand marijuana & tobacco smoke.

-The marijuana joint’s emission rate was 3.5 times that of the tobacco cigarette.

-All the cannabis sources had PM2.5 emission rates greater than tobacco cigarettes.

-The order of cannabis emission rates was joint, bong, glass pipe, and vaping pen.

-The vaping pen’s mean decay rate exceeded the other sources’ mean decay rates.

Secondhand bong smoke is worse than that from tobacco.

March 30, 2022

The fine particulate matter in cannabis smoke from bongs is at least four times greater and more dangerous


Conclusion: Metabolites of marijuana smoke can be
detected in children; in this cohort, 16% were exposed.
Detectable COOH-THC is more common in children with
tobacco smoke exposure. More research is needed to assess
the health impacts of marijuana smoke exposure on children
and inform public health policy.

Wilson KM, et al. Detecting biomarkers of secondhand marijuana smoke in young children. 2017;81(4):589-592. Doi:10.1038/pr.2016.261


Approximately half of the children who qualified for our study had biological evidence of exposure to marijuana. Researchers in studies such as this provide valuable data on secondhand exposure to children from parents using tobacco and marijuana and can inform public health policies to reduce harm.

Wilson KM, et al. Marijuana and tobacco coexposure in hospitalized children. 2018;142(6):1-7. Pediatrics. e20180820

Conclusions: One minute of exposure to marijuana SHS substantially impairs endothelial function in rats for at least 90 minutes, considerably longer than comparable impairment by tobacco SHS. Impairment of FMD does not require cannabinoids, nicotine, or rolling paper smoke. Our findings in rats suggest that SHS can exert similar adverse cardiovascular effects regardless of whether it is from tobacco or marijuana.

Wang X, et al. One minute of marijuana secondhand smoke exposure substantially impairs vascular endothelial function. 2016;5:e003858 doi:10.1161/J Am Heart Assoc.116.003858 

Second-hand marijuana smoke is not benign.

Here are three important facts from these articles for your consideration.     

  1. One out of six or 16% of children under 2 years of age, hospitalized with bronchiolitis in Colorado between 2013-2015, were found to have marijuana products in their blood, indicating prior exposure to the drug. 
  2. Approximately 50% of hospitalized Colorado children whose parents were in a smoke cessation program also showed biologic evidence of exposure to marijuana.  
  3. In animals, only one minute of exposure to secondhand marijuana smoke substantially harms vascular function for at least 90 minutes, suggesting that secondhand marijuana smoke can harm the heart and blood vessels just as we know secondhand tobacco smoke contributes to heart attacks and peripheral vascular disease.