Here is what we know from a scientific point of view: There is no amount of wood smoke that is good to breathe. It is at least as bad for you as cigarette smoke, and probably much worse. (One study found it to be 30 times more potent a carcinogen.) The smoke from an ordinary wood fire contains hundreds of compounds known to be carcinogenic, mutagenic, teratogenic, and irritating to the respiratory system. Most of the particles generated by burning wood are smaller than one micron—a size believed to be most damaging to our lungs. In fact, these particles are so fine that they can evade our mucociliary defenses and travel directly into the bloodstream, posing a risk to the heart. Particles this size also resist gravitational settling, remaining airborne for weeks at a time.

Once they have exited your chimney, the toxic gases (e.g. benzene) and particles that make up smoke freely pass back into your home and into the homes of others. (Research shows that nearly 70 percent of chimney smoke reenters nearby buildings.) Children who live in homes with active fireplaces or woodstoves, or in areas where wood burning is common, suffer a higher incidence of asthma, cough, bronchitis, nocturnal awakening, and compromised lung function. Among adults, wood burning is associated with more-frequent emergency room visits and hospital admissions for respiratory illness, along with increased mortality from heart attacks. The inhalation of wood smoke, even at relatively low levels, alters pulmonary immune function, leading to a greater susceptibility to colds, flus, and other respiratory infections. All these effects are borne disproportionately by children and the elderly.

The unhappy truth about burning wood has been scientifically established to a moral certainty: That nice, cozy fire in your fireplace is bad for you. It is bad for your children. It is bad for your neighbors and their children. Burning wood is also completely unnecessary, because in the developed world we invariably have better and cleaner alternatives for heating our homes. If you are burning wood in the United States, Europe, Australia, or any other developed nation, you are most likely doing so recreationally—and the persistence of this habit is a major source of air pollution in cities throughout the world. In fact, wood smoke often contributes more harmful particulates to urban air than any other source.