Background:
The current study, part of the EU H2020 funded TackSHS project, aimed to test the hypothesis that passive exposure to e-cigarette emissions provokes systemic symptoms and to determine their severity and timing.

Methods:
30 nonsmokers, 18-35 years old, BMI< 30, with no significant medical history, no medications, normal physical examination and spirometry, were passively exposed in a 35m³ room, during a 30-minute Control (no passive smoking) and Experimental (standardized e-cigarette smoking by a human smoker) session.
PM_2.5 concentrations were 0.027 mg/m³ and 3.3 mg/m³ during the Control and Experimental sessions, respectively. Participants completed an irritation questionnaire, grading symptom severity at T₀ (pre-exposure), T₁₅ (midway), T₃₀ (exposure endpoint) and T₆₀ (30-minute post-exposure) in both sessions.
The questionnaire showed internal consistency (Cronbach's α>0.70). Scores 1-5 were generated for the environmental, ocular, nasal, airway and general complaints by adding symptoms per system. Analysis was performed using Wilcoxon-signed rank sum test and Spearman correlation (p< 0.05).

Results:
The most frequent and intense symptoms reported were mild eye burning, nasal and airway dryness.
Ocular irritation score gradually increased from T₀ reaching a significant increase by T₃₀ (p=0.034). Nasal score increased significantly from T₀ to T₁₅ (p=0.008) and remained significantly higher at T₃₀. Airway irritation score increased significantly from T₀ to T₁₅ (p=0.004) and furthermore from T₁₅ to T₃₀ (p=0.018). All symptoms returned to T₀ scores by T₆₀ (p>0.05).
The increased scores for ocular, nasal and airway complaints were positively correlated with increased environmental scores at T₁₅ and T₃₀. General complaint scores showed a tendency to increase at T₃₀ that was positively correlated with increased environmental scores at T₃₀.

Conclusions:
Short-term exposure of nonsmokers to e-cigarette emissions resulted in mild ocular, nasal and airway symptoms that persisted up to 30 minutes and were positively correlated with environmental indices. Further research is needed to investigate long-term health implications.