Gas stoves and cognitive development: What the research shows.

If you spend any time among parents, at least in bougier circles, you’ll know that protecting your kids from environmental toxins is a passion bordering on obsession. Lengthy discussions ensue about which brand of BPA-free plastic water bottles to use, how to find crib mattresses that don't off-gas volatile organic compounds, or whether it's worth getting a vacuum cleaner with a HEPA filter. Now, some parents are starting to worry about their gas stoves.

A third of American homes—some 46 million—have gas stoves. People in the U.S. are indoors and at home about 70 percent of their time. This means gas stove emissions could add up to a serious pediatric public health issue. "I’ve been working on cooking-related pollution for quite a few years now," said Stephanie Holm, co-director of the Pediatric Environmental Health Specialty Unit at the University of California, San Francisco. "And I always say to folks that it's one of the most underappreciated exposures that our kids have."

Gas stoves are a major source of indoor air pollution, releasing a toxic potpourri of inhalable particulate matter, nitrogen dioxide, formaldehyde, and methane. Some of these chemicals are cause for environmental concern—methane, for one, is a potent greenhouse gas. But headlines have also raised health concerns: Gas stoves may worsen asthma in children and can release numerous carcinogens (though in low concentrations), even when turned off.

It's understandable that parents might be tempted to rip these appliances out of the walls immediately—there are a ton of reasons to lightly fear them. I have my own particular worry to add to the mix. As a neuroscientist living in an old, unventilated apartment with a 4-year-old, I can't help but wonder: How does cooking my kid a quesadilla affect his brain? And, since I can't simply replace my stove, what can be done to mitigate its general ill effects on our health?

Neuroscience research suggests several ways that air pollution in general could damage the developing brain. In the womb, particulates inhaled by the mother can cross the placental barrier. The kind of particulates liberated during cooking can be covered in toxic substances and heavy metals that can accumulate in fetal tissue. The developing brain hasn't learned to dispose of these metals yet, leaving it particularly vulnerable to damage.

After birth, contaminated air enters children's bodies via their lungs, and from there, toxins can cross the blood-brain barrier to trigger inflammatory and oxidative stress responses. Certain pollutants may be shuttled from the nose directly into the brain, bypassing the blood-brain barrier entirely. Brain-imaging studies find pathological abnormalities in children exposed to significant air pollution, including thinning of the cortex, disorganized connectivity, and unusual sizes for certain brain areas.

But do these scary-sounding biological processes translate into real-world issues with brain health when it comes to pollutants from gas stoves? It seems only two studies empirically weigh in on this question, both conducted by the same group in Spain. In one study, the group found that the presence of a gas cooker in the home was associated with a very, very small drop in scores on a cognitive development test administered to 1-year-old infants (think a few points out of 100; nowhere near enough to put your typical kid in "cognitive delay" territory). But this study didn't measure air quality in homes directly, so it's unclear if the score drops were simply because people who cook with gas stoves are systematically different from people who cook with electric stoves.

Another study by the same group is more conclusive. In this study, field workers went to 500 homes with newborns and directly measured indoor nitrogen dioxide concentrations for three months. (Nitrogen dioxide—a major pollutant of traffic—is only released by gas stoves, not other cooking devices.) Then, four years later, they tested the children's mental functioning and attention-hyperactivity behaviors. Kids who lived in homes with gas stoves experienced levels of nitrogen dioxide triple to those who came from homes with electric stoves. Kids from homes with gas stoves fared marginally worse on cognitive tasks (again, a point or two out of a 100-point scale). But the higher the nitrogen dioxide levels, the worse the children did—suggesting the small effect is truly due to toxins released by the stove. Children in homes with gas stoves also had a slightly higher risk of developing some ADHD symptoms. The researchers controlled for all sorts of confounding factors such as social class, location, and outdoor nitrogen dioxide levels, making these results convincing.

But these are only two studies, and the cognitive and behavioral effects were really small. To put it in perspective, having smokers in the household, or lead in pipes, would be far more damaging. Yu Ni, a postdoctoral scholar at the University of Washington, recently published one of the largest, most-rigorous studies of outdoor air pollution in the U.S. Her group found that outdoor air pollution was associated with cognitive and behavioral problems, but Ni said that the magnitude of the changes were relatively small. "Lifestyle behaviors or genetic factors probably have a much larger impact on specific groups of people," Ni said.

So what are parents to do with this information? As a scientist, I’m reluctant to make a major decision like ripping out an appliance based on two studies, even if the more robust evidence from outdoor air pollution strongly suggests the indoor harm to developing brains is real. I’m more compelled by the studies linking gas stoves to asthma and respiratory problems, but even this literature isn't a slam dunk.

Another issue is it's difficult to separate the effects of gas stoves specifically to cooking more generally. Holm recalled baking cookies with her daughter with an indoor air quality monitor on hand, and she was shocked to find that "With just one batch of a dozen cookies, we managed to get our indoor particulate matter levels up into the same range that you would see from wildfire smoke. Very unhealthy levels." The kicker: Holm has an electric oven. In other words, cooking, regardless of heat sources, is a combustion process that releases chemicals and particulate matter, all contained in a small space. Yes, gas stoves likely make air quality even worse because they release additional chemicals, but it's not clear how much more that pollution exacerbates what's already a pretty small effect on brains. If you’re inclined to ruminate over whether your gas stove is going to hobble your child's chances at Harvard, maybe just spend that energy reading a book to your kid instead.

In some areas, the fretting over the health impacts of gas stoves may become moot. Several cities, including New York City, are banning installation of gas heaters and appliances in all new buildings in the name of environmental sustainability. Gas stoves release the powerful greenhouse gas methane, even when turned off. But gas bans are really part of a broader push for cities to replace fossil fuel infrastructure with cleaner electric grids. Because many of the highly publicized reports about the health impacts of stoves are put out by climate advocacy groups and allied think tanks, some are suspicious that the health risks to individuals are being exaggerated as a scare tactic to get people to switch appliances for climate reasons. Maybe so, but you could view a switch as a win-win: An electric stove reduces a small brain risk and a small environmental emission all in one go. On a population-wide level, the shift to electric appliances could be meaningful for both public health and climate change.

Even though cooking may only pose a marginal risk to your child's brain, it's still worth taking some simple steps to make a small risk smaller, particularly if you or someone living with you is pregnant. Only a third of people with exhaust hoods say they regularly use them. It might be easy to think that hoods are just there to remove strong odors, or to flip on when food is burning. But exhaust hoods are meant to help with all toxins: In the studies above on household pollution, the more people reported using an exhaust hood, the lower the levels of household nitrogen dioxide. Holm thinks an education campaign could go a long way. "A lot of times people think, ‘Oh, you know, sure if I’m burning bacon, I turn [the exhaust hood] on. But other times I’m cooking, I don't need it.’ And that's not true. You really should be using it every time you cook." Her group has just released a video tutorial about best practices in ventilation while cooking.

For those, like me, who don't have an exhaust hood and can't install one, you can pick up a $25 box fan facing out a nearby window to pull the fumes out. I tried this out. To see if the ventilation was working, I picked up an air quality monitor and tested cooking with and without the fan: With the fan running, pollutants in the kitchen didn't reach stratospheric levels, and the air cleared in 20 minutes or so. Without the fan, the airborne pollutants lingered for over an hour. I also added air purifiers in other rooms just to generally clean the air, but they have the bonus of filtering out residual particles from the stovetop. Not everyone can afford air purifiers, but a box fan is within most people's reach. At minimum, you can utilize a tried-and-true (and free) air quality improvement tactic: just open the window.