Cooking veggies

This article was originally published on July 7, 2021, but has been updated with current information.

Can cooking be bad for your health? Scientists say yes.

A paper published in December 2022 states that cooking on gas stoves accounts for 13 percent of asthma cases in children in the U.S. By sending a shower of polluting particles into the air, these cooktops pose a “significant public health burden,” according to the study.

The Consumer Product Safety Commission responded quickly to these results by announcing plans to strengthen voluntary safety standards for these stoves in January 2023. Yet this concern about the potential risks associated with cooking is not entirely new.

Like many people, Stephanie Holm made holiday cookies with her family in 2020. Her daughter found a recipe online and the two set about making the treats in their apartment kitchen.

Together, they kneaded the dough, rolled it out, put the cookies on a sheet pan and popped it in the oven — “literally sprinkles on the outside … sweet and very tasty,” says Holm, a pediatric environmental medicine specialist at UC San Francisco.

But while the cookies were baking, Holm noticed that the sweet sugar coating had burned a little in the oven, but not enough to ruin the cookies. Then Holm heard her daughter exclaim, “Mom, it’s purple!” and she saw that the air quality sensor she keeps in their apartment had indeed changed from green (good air quality) to purple (very unhealthy) . Could a batch of lightly fried cookies be to blame?

What happened to Holm’s cookies was no accident. All cooking releases a complex mixture of chemicals, some of which would be classified as unhealthy pollutants. As for whether cooking is dangerous to your health – the short answer is, it depends. But generally if you have good ventilation you should be fine.

“We all cook, and the average life expectancy is 78 or 79 years. So we shouldn’t worry too much,” says Delphine Farmer, an atmospheric chemist at Colorado State University. “But it’s an opportunity to think about how to reduce your exposure to pollutants.”

Out of the pan

The farmer’s study found that cooking releases a mixture of hundreds of different chemical compounds into the air. Each ingredient emits its own unique mixture of particles and gases. Proteins in meat can break down and release ammonia. Baking can produce isocyanates. Oils from frying and sauteing can aerosolize (thus leaving your counters with a thin layer of grease on them). Molecules in the air can continue to react and change as they drift around your kitchen and bump into each other.

“You can see some of these really interesting compounds,” Farmer says. “But are they at levels that are toxic?” We don’t know.”

Part of the uncertainty when it comes to health impacts comes from the fact that most air quality studies and standards are based on outdoor air—despite our world today, where people spend about 90 percent of their time indoors. While Canada and on World Health Organization have indoor air quality guidelines, the US does not.

In general, the chemical composition of indoor air fluctuates much more than outdoor air. Average air quality may be good, but as Holm and her daughter have experienced, certain activities — like cooking and cleaning — can cause dramatic changes. Pollutant levels will spike in the kitchen while cooking is actively underway and then drop back down as the molecules in the air disperse.

“The exposure pattern is different. And we really don’t have big scientific data on what this difference in exposure pattern means for people’s health,” says Holm.

Acquiring this scientific data is not an easy task. Variables that can affect cooking fumes and their content include how often a person cooks, what he cooks, how he cooks it, what kind of appliance he uses, what kind of ventilation he has and maybe even the kind of pots and pans he uses, he says Ian Walker, an engineer at Lawrence Berkeley National Laboratory who studies indoor air quality and ventilation. The best researchers can do is try to gauge the relative impact of each factor: gas stove or electric? Boiling or frying? Meat or vegetables? Nonstick or stainless steel pan?

Read more: Standing next to your microwave is not dangerous

In the fire

The main pollutant of concern associated with cooking is dust particles. This catch-all term refers to a complex combination of microscopic solid particles and ultrafine liquid droplets that can be composed of hundreds of different chemical compounds. Chemistry is not as important as size. Particles smaller than 10 microns (less than 1/5 the width of a human hair) can make their way into the lungs and stay there. Even smaller particles can make their way into the bloodstream.

Particulate matter is why you don’t want to breathe in car smoke or exhaust. Chronic exposure to high levels of particulate matter worsens asthma, but it also makes it more likely that a child will develop asthma, Holm says. It is also associated with changes in childhood growth, metabolism and brain development and is classified as a a carcinogen from the WHO.

All cooking produces some particles in the form of aerosols and small pieces of char generated from food and dust that are heated. If you smell something burning, you’re probably inhaling a lot of dust particles. “Anything with a red-hot element will generate particles,” Walker says. This includes most stoves, ovens, and even small appliances like toasters. Both frying and baking cooking methods produce far more particles than boiling or steaming. And fatty foods release more than vegetables.

Gas stoves are particularly bad for indoor air quality. Not only do they produce more particulate matter due to the creation of an open flame, but the actual burning of fossil fuels also generates other gases, such as carbon dioxide and nitrogen dioxide. From a health perspective, the thing of greatest concern in this scenario is nitrogen dioxide.

Nitrogen dioxide, like particulate matter, contributes to breathing problems such as asthma and is regulated in outdoor air. The gas has also been linked to heart problems, lower birth weight in newborns and shorter life expectancy in people who are chronically exposed.

A 2016 study from Lawrence Berkeley National Laboratory found that simply boiling water on a gas stove produced nearly twice the amount of nitrogen dioxide the EPA external standard. That being said about a third of American homes use natural gas for cooking, this is a large potential exposure.

“We’ve kind of gotten used to an unvented fossil fuel unit in our homes,” says Brady Seals, who runs the carbon-free buildings program at the Rocky Mountain Institute, a clean energy think tank. She wants to raise awareness about nitrogen dioxide health risks as a way to discourage the use of natural gas in homes.

And she is not alone in this mission. The Massachusetts Medical Society accepted resolution in 2019 to recognize the link between gas stoves and pediatric asthma. Several cities in California, incl San Franciscopassed bans on natural gas in new construction, citing both climate and health hazards.

If you have a gas stove, Seals and Walker recommend replacing it with an electric one if you have the means and ability to do so. “You’re not just reducing your carbon footprint [on the environment]but you can have a healthier home if you get rid of combustion appliances,” says Walker.

The best option for both energy efficiency and air quality, he says, is an induction stove, which uses magnets to transfer heat directly to your pots and pans. No incandescent means less dust particles. If you can’t replace your gas stove, Seals recommends a plugin induction cooking surface.

Ventilated air

Realistically, few people will swear off stir-frying or using their oven for the sake of producing fewer particulates. “Everybody’s going to cook what they’re going to cook,” Farmer says, noting that people use whatever kitchen appliances they have. That’s why all these experts emphasize the importance of good ventilation.

Holm was part of a 2018 survey looking at particulate matter in the homes of children with asthma. One of the most surprising findings: In homes that never used a hood or fan, people were exposed to unhealthy levels of particulate matter for roughly 10 percent more time than in homes that used ventilation.

Walker, the ventilation expert, recommends that people use a high setting on their kitchen hood whenever possible, as quieter low settings only capture about half of the pollutants. Since most hoods do not extend above the front burners, you may want to consider using the back burners, especially if you have a gas stove. Walker also advises people to keep the vent on for about 15 minutes after they finish cooking. Approximately this time is needed to change all the air in the room. But this only applies if your vent is sending fumes outside, which doesn’t happen often.

Unless you have a new kitchen and a higher-end stove, your built-in vent may be essentially a fan. It’s just pushing the vapors around the room, which helps disperse the concentration of pollutants faster, but doesn’t actually remove them from your house. Many homes and apartments, including Holm’s, don’t even have that option. In this case, Holm recommends opening some windows if the outside air quality is good, or using a portable air purifier with a HEPA filter.

After all, there are still many unknowns about how cooking fumes affect us. To some extent, we just have to accept them as a byproduct of enjoying our favorite foods, much like we accept pet hair as part of having a furry friend. “You start to realize how pollutants are part of our lives,” Seals says. “Let’s reduce pollution wherever we can. But I won’t give up my dog ​​and I won’t stop cooking.”

[Correction: A previous version of this story erroneously stated the findings of Holm’s 2018 air quality study and the type of portable air purifier that Holm recommends using in homes. We apologize for the errors, which have been corrected in this current version.]

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