Winter Indoor Air Pollution: Expert Advice for Healthier Homes

As an especially fierce winter blankets much of the U.S. in snow, ice, and subzero temperatures, many of us are spending more time indoors to escape the cold. But indoor air contamination can be most dangerous in the winter months, when we’re lighting more candles, using fireplaces, or simmering warm foods on a gas stove.

Burning anything indoors releases gasses, volatile organic compounds, and particulate matter, tiny particles that can enter the bloodstream and are linked to respiratory health issues. Some cleaning and personal care products can also release chemicals linked to developmental issues in children.

We spoke with Jonathan Levy, an environmental health scientist at Boston University, and Gabriel Bekö, environmental engineer at the Technical University of Denmark, about how they keep their homes both cozy and safe.

Ferrari: Most of us think of pollution as something we’re exposed to outside, from sources like car tailpipes or power plant smokestacks. Should we be worried about the air inside our homes too?

Bekö: The World Health Organization estimates that indoor air pollution can be two to five times higher than outdoor [air pollution].

Many of the chemicals we have indoors are coming from indoor sources, from consumer products. A lot of it is from personal care products, but there are other sources like combustion—if you have gas burners, if you have candles, for example. Cooking generates chemicals and particles.

Levy: One indoor pollutant we think about a lot is particulate matter, which comes from combustion of different fuels in homes. It can come from cooking, cigarette smoke, candles—anything where you’re generating a flame or burning something. Particulate matter is known to contribute to a lot of different health effects, including respiratory and cardiovascular disease.

Nitrogen dioxide is another one we think about a lot, which comes from burning gas, so gas stoves are an important source of nitrogen dioxide indoors.

Ferrari: Have you changed any habits in your home since you started studying this topic?

Levy: I try to be conscious during the cooking process. Things everyone does pretty intuitively: if you’re cooking something very smoky open some windows, even if it’s cold outside, to air things out as quickly as possible. Indoor spaces [can improve with] a portable air cleaner, or if you have an HVAC system in your home, have a good air filter running through that.

Three things that affect your indoor air quality when burning things are: How much are you burning and for how long? What is the ventilation? And how big is your home and the space? The larger the space, the more dilution you get, so smaller homes and apartments do amplify the effect of any indoor source of pollution.

We’ve [in my home] taken all those steps. It’s impossible to get pollution down to zero, but we try to be conscious of good ways to reduce exposure where we can.

Bekö: I try to avoid chemical exposures. I’m not so worried about particles that come from cooking; of course I turn on the exhaust hood. And I open windows in the bathroom after every shower to stop mold growth.

But what worries me most are endocrine-disrupting chemicals, chemicals that mimic hormones. When my kids were small, I really tried to avoid fragrances. My personal care products are unscented or fragrance-free. My laundry detergent is fragrance-free as well.

Ferrari: Are there any products or habits you strictly avoid?

Bekö: If it’s very clearly stated that something is phthalate free, or BPA free, I try to look for it. I always buy fragrance-free products, even though I’m not sure how big of an impact it has on long-term health.

I also limit burning candles. In Danish homes, people burned a lot of candles every evening for hours. We did a study here in the winter months showing that particulate matter concentrations linger for hours after blowing out a candle.

It’s a good idea to open the window after the candles are blown out; combustion particles contain carcinogenic compounds. I’m not saying you’re going to get sick if you burn candles, but why not avoid it when we know some of those compounds are not good for you?

Levy: Everybody’s lifestyle is different. It’s a question of: what do you need to do versus what do you like to do? What things could you eliminate without great harm? If you don’t have a need to burn incense in an indoor space, you don’t need to do it, but if it’s something that’s important for your lifestyle or traditions, do it for a shorter amount of time and make sure you have ventilation and filtration running.

Ferrari: What are manageable changes concerned readers could make to their homes?

Bekö: What’s really important, and not appreciated enough, is ventilation. Opening windows regularly, even in the winter months, at least several times a day for five to ten minutes is beneficial. It might be drafty, but it’s a balance between comfort and health.

Filters should be regularly changed and maintained, and ventilation ducts and systems should also be maintained properly to avoid pollution buildup.

Removing dust also removes chemicals. Washing surfaces, floors, walls, windows—you remove chemicals, so cleaning is a good thing.

Levy: Not having the source at all is the best way to eliminate its contribution, but that’s not always realistic––people have to cook. Some people like lighting candles; you can’t eliminate all sources of pollution.

When you have sources of indoor pollution present, the key is ventilation and filtration. If you’re cooking, you want to run an exhaust fan that vents to the outdoors. If you don’t have an exhaust fan that vents to the outdoors, opening some windows nearby can help.

If people stop and think, “How many hours a day do I spend inside?” people realize most of their time is spent inside their home. You can influence what’s happening in your own house, so that gives you some control and authority over the levels of exposure that you and your family face.