The burning of biomass fuels such as wood and crop residues, which are often used for cooking and heating homes in rural China, contributed to 32% of an estimated 1,150,000 premature deaths caused by inhaling fine particle pollutants in China in 2014, according to a new study. Residential energy use of all types led to 67% of these premature deaths overall, the findings suggest. Previous studies have tended to focus exclusively on concentrations of PM2.5 (particles with a diameter of less than 2.5 micrometers, which pose the greatest health risks when inhaled) in the outdoor air, excluding indoor environments where people spend most of their time. And while evidence does increasingly suggest indoor residential fuel emissions pose significant dangers, results from previous research focused on indoor environments have varied widely due to a lack of detailed, reliable data on residential emissions. To systematically study residential PM2.5 exposure in China, Xiao Yun and colleagues modeled variations in emissions based on energy type (including coal, biomass, and clean energy), activities (such as cooking and heating), geographic areas (urban and rural), and location (indoor and outdoor). They found that average indoor PM2.5 concentrations in Chinese households were 3 times higher than outdoor air concentrations and that rural indoor air levels of PM2.5 were about 1.6 times higher than those in urban indoor air. Yun et al. also concluded that energy use for cooking and heating led to similar health impacts, noting that current plans to mitigate PM2.5 exposure in China do not account for cooking emissions.