About 1.5 million years ago, our ancestors Homo erectus learned to light fire from wood to keep wild animals away. Over the years, the human race has used several biologic sources of fuel to produce fire, not only for getting rid of enemies but also for cooking and heating. These sources have included wood, charcoal, dried twigs and grass, crop residues, and animal dung cakes, which collectively are called biomass fuels. Although the modern world has replaced these highly polluting fuel sources with cleaner sources, such as liquefied petroleum gas and electricity, it is estimated that ~ 50% of all households worldwide and 90% of all rural households continue to use biomass fuel as their main domestic source of energy.1 Even in some developed countries, such as Canada, Australia, and the western states of the United States, the persistent rise in cost of energy has prompted an increasing number of households to use wood or other biomass fuels for cooking and heating purposes.2 For example, a recent study in New Mexico reported that 26% of the population was exposed to smoke from biomass fuel.3 According to estimates, > 2 billion kg biomass are burned every day worldwide4 in open fires and inefficient stoves in poorly ventilated rooms, making biomass smoke one of the most important sources of indoor air pollution globally. Moreover, biomass burning also contributes significantly to outdoor air pollution,5 thereby exposing many nonusers to biomass smoke components.