Short answer
Secondhand cannabis smoke is harmful. Secondhand cannabis vape aerosol is a smaller risk, but not zero. Smoke from a burning joint, blunt, or pipe carries carbon monoxide, tar, benzene, and fine particles. A vape pen heats a liquid with no combustion, so it releases THC, solvents, and flavorings instead. Research on vape aerosol is thin. No US agency has set an exposure limit for secondhand cannabis in either form.
What is in secondhand smoke
A joint burns between puffs. Most of that smoke goes into the room, not the smoker's lungs.
what are the health risks of secondhand weed smoke
- Combustion products: carbon monoxide, benzene, formaldehyde, acrolein, and PM2.5 particles.
- THC. A 2015 study placed six nonsmokers in a car with cannabis smokers for one hour. All six had THC metabolites in urine afterward. In a ventilated room, fewer did.
What is in secondhand vape aerosol
A vape pen heats a liquid. The exhaled cloud holds THC, terpenes, propylene glycol, vegetable glycerin, and flavorings. Particles are smaller than smoke particles, which lets them reach the deep lung.
secondhand thc smoke from neighbors living in apartments
Illicit THC cartridges have contained vitamin E acetate. The CDC tied that compound to the EVALI outbreak. As of February 2020, states reported 2,807 hospitalized cases and 68 deaths.
THC in exhaled aerosol is real but lower than in smoke. Air in a closed room where someone vapes shows detectable THC within minutes. Measured levels drop fast after the device stops.
Who faces the most risk
- Children. Urine tests of children in homes where cannabis is smoked indoors have shown THC metabolites.
- Pregnant people. THC crosses the placenta.
- People with asthma, COPD, or heart disease.
- Infants held against clothing that holds smoke residue.
Thirdhand residue
THC sticks to walls, carpet, and furniture. A 2022 study of homes found THC on surfaces and in dust where cannabis was smoked indoors. Residue fell over weeks but did not clear fast. Nicotine residue lasted longer than THC residue in the same homes.
How to lower exposure
- Use outdoors or on a balcony.
- Open windows and run an exhaust fan. HEPA filters capture particles, not THC gas.
- Do not vape in a car with passengers.
- Keep children and pets out of rooms where cannabis is smoked.
- Change clothing and wash hands before holding a baby.
What is unknown
No study has set a dose response curve for secondhand cannabis vape aerosol in humans. Long term studies of adults exposed to aerosol alone do not exist. Open air exposure near one vape pen is low. A closed room with repeated sessions is the case to watch.
Convenience and exposure
Vape pens cut smoke and smell. That makes indoor use easier, and indoor use is where secondhand THC concentrates. The same session outside disperses with the air.