How serious is indoor air pollution (IAP) a mortality threat to young children? This paper estimates the causal effect of cooking fuel choice – a predominant cause of IAP – on infant mortality in India (1992-2016), where the most health-endangering biomass fuels are also most commonplace. Leveraging the speed of change in forest cover and land ownership for identification, we find polluting fuel choice to impose highly heterogeneous local infant mortality effects by age group (from insignificant to 4:7 percent increase) – implying the loss of two lives every 1,000 live births. These conclusions are robust to alternative estimation strategies and additional controls.