Winter brings more air pollution inside. Here’s how to minimize your risks.

Burning—wood, gas, or candles—fuels unhealthy air pollutants

Combustion pollutants—released from burning oil, kerosene, gas, coal, or wood—are another prime source of winter’s indoor toxins.

Nitric oxide and volatile organic compounds irritate the eyes, nose, and throat and, in extreme cases, damage the central nervous system. Burning also produces fine particulate matter or PM2.5s—particles with a diameter of 2.5 micrometers or less. If these particles make it to the bloodstream or deep in the lungs, they’ve been linked to respiratory and heart disease, as well as complications from respiratory viruses.

Half of the PM2.5s in an average home come from outdoor pollutants that make their way inside, but the other half originate internally from burning.

Wood-burning stoves and fireplaces used to heat homes are some of the worst offenders. Propane fireplaces generate PM2.5s as well, though in lower quantities because more are burned off with the gas. 

Of course, these devices vent to a home’s exterior, but some particles nonetheless remain in the room. And in older homes where air regularly moves through cracks and joints and around windows and doors, “some of the particles that are vented outside can come back in,” Nassikas says.

Even candles release combustion pollutants. One study of several dozen Danish homes in winter found that extensive candle use for hours a day caused almost 60 percent of the particle exposure in those homes.

Cooking is a major source of particulate pollution

Most of us do much of our burning in the kitchen, and not only when we leave bread too long in the toaster. All cooking involves heat that generates a large amount of indoor pollutants. Gas stoves are especially problematic, because they release nitrogen dioxide and formaldehyde that affect a person’s airways. Nearly 13 percent of childhood asthma cases in the U.S. have been linked to gas stoves; in some states, like Illinois and California, the figure is closer to 20 percent. 

But electric stoves aren’t off the hook. If you smell something burning when you turn on the stove, “that’s the crud that’s left over and becomes aerosolized when heated to high temperatures,” releasing particulate matter, Nassikas says.

The other factor is what’s for dinner. Stews, casseroles, fried chicken, and other fatty fare may warm your insides on a cold winter evening, but they also generate numerous PM2.5s. Frying on the stove is the most polluting, but baking in the oven carries risks, too.