"The first thing we swallowed every morning was smoke," Marco Tulio Guerra, a native of rural Guatemala, tells Nat Geo. In places like rural Guatemala, open-fire cooking is often a necessity, as many households are unable to afford fuel for safer gas ranges. Wood-burning open fires give off the same mount of smoke as 20 packs of cigarettes per hour, which makes smoke inhalation a major health risk in poorly-ventilated homes. According to the EPA, smoke inhalation can lead to heart and lung diseases, as well as a long list of respiratory problems. However, health concerns aren't the only negative byproduct of cooking with an open fire—the demand for firewood exacerbates an already serious strain on local forests, and the smoke emissions contribute to global warming.