Nicotine Absorption in Bystanders
EVIDENCE: HIGH A landmark 2024 study published in Environmental Health Perspectives measured cotinine (a nicotine metabolite) in the urine of non-vapers exposed to secondhand aerosol for one hour in an unventilated room. Result: detectable but trace levels — 10-50x lower than cotinine levels found in secondhand smoke exposure studies. In well-ventilated spaces, cotinine was below the detection limit.
Respiratory Effects
EVIDENCE: MODERATE A 2025 systematic review in the European Respiratory Journal analyzed 18 studies on respiratory effects of secondhand vape exposure. Findings: short-term exposure (1-2 hours) caused mild airway irritation and a small decrease in FEV1 (lung function) in some subjects, particularly those with pre-existing asthma. No long-term respiratory effects have been documented in non-vapers. This is a much milder profile than secondhand smoke, which has proven causal links to asthma exacerbation and lung cancer. For more on respiratory science, see our lung health research guide.
Cardiovascular Effects
EVIDENCE: LOW Limited studies have examined cardiovascular effects of secondhand vape. A 2025 pilot study (n=24) found no acute changes in blood pressure or heart rate in non-vapers exposed for 30 minutes. This contrasts sharply with secondhand smoke, which causes immediate endothelial dysfunction and is causally linked to heart disease. More research is needed — current evidence does not support cardiovascular harm from secondhand vape, but the evidence base is thin.
Cancer Risk
EVIDENCE: HIGH (for absence of evidence) No study has found a causal link between secondhand vape exposure and cancer. The IARC (International Agency for Research on Cancer) has not classified secondhand vape as a carcinogen. The absence of tobacco-specific nitrosamines and combustion byproducts (the primary carcinogens in secondhand smoke) makes a significant cancer risk biologically implausible at observed exposure levels. However, long-term exposure data (20+ years) does not exist because vaping is relatively new.
