Characterization of Indoor Volatile Organic Compound Emissions From Essential Oils and Assessment of Inhalation Health Risks

People spend much of their time indoors, where heated essential oils affect indoor air quality. However, emissions of derivative volatile organic compounds (VOCs) from long‐stored essential oils (> 5 years) remain underexamined. This study evaluated tea tree and rose oils using chamber tests and indoor field monitoring to quantify VOC time‐weighted average (TWA) concentrations and assess exposure risks. Heating long‐term stored oils generated derivative VOCs, with a notable shift toward aromatic and oxygenated compounds, with ethylbenzene reaching 125–226 ppb. The associated cancer risks ((4.12 − 4.68) × 10 −5 ) fall within the commonly cited risk‐management range (10 -6 –10 -4 ). Accordingly, heating long‐term stored essential oils is not recommended for indoor use. By contrast, hazard index (HI) estimates for 3‐ethylbenzaldehyde (another degradation product) and outdoor‐derived toluene indicate limited acute respiratory risk under typical usage conditions (HI < <1). To reduce exposure, nonheating diffusion methods (e.g., stick diffusers or ultrasonic water‐based nebulizers), combined with good ventilation, shorter diffusion durations, and lower oil loadings, are recommended. This study underscores the need for proper storage (airtight, light‐protected, and cool) and realistic shelf lives and cautions against heating long‐stored oils indoors due to the potential for elevated VOC emissions. These findings highlight the importance of incorporating storage‐related emission risks into indoor air quality management and product labeling guidelines.