Outdoor air quality has improved in many cities around the world as people shelter in place to help control the spread of the novel coronavirus. Fewer cars on the road have led to dramatic reductions in fine particulate matter like soot in the air in places like Delhi, India, but as we all continue to spend an increasing amount of time in our own residences, it’s worth considering the effects of indoor air pollution, too.

If you have a gas-powered stove, furnace, or water heater at home, you might want to take a look at a recent study by the UCLA Fielding School of Public Health, which points to some pretty concerning potential health effects that could worsen COVID-19 outcomes.

The study found that gas appliances emit a wide range of air pollutants, including carbon monoxide, nitrogen oxides, particulates, and formaldehyde, all of which have been linked to acute and chronic conditions like respiratory illness, cardiovascular disease, and premature death.

“Under a hypothetical cooking scenario where a stove and oven are used simultaneously for one hour, peak concentrations of NO2 [nitrous dioxide] from cooking with gas appliances exceed the levels of acute national and California-based ambient air quality thresholds in more than 90 percent of modeled emission scenarios,” states the report. “Concentrations of CO [carbon monoxide] and NO2 resulting from gas cooking are the highest for apartments, due to smaller residence size. This presents an additional risk for renters, who are often low-income.”

These concentrations are often amplified by poor ventilation, as many homes in California and the rest of the U.S. lack range hoods or any proper type of ventilation system. Old and unmaintained appliances, small residences where air pollution can reach higher concentrations, and the use of kitchen appliances as supplemental heating by people who can’t afford more conventional heating sources in winter (or lack them altogether) also worsen the effects.

The study also looked at outdoor air quality. Assuming all indoor emissions are transported outside, it found that about 12,000 tons of carbon monoxide and 15,900 tons of nitrogen oxides were emitted into the air through the use of residential gas appliances in California in 2018. But if all of these gas appliances were immediately replaced with clean electric alternatives, the ensuing reduction in outdoor air pollution would result in 354 fewer deaths, 304 fewer cases of chronic bronchitis, and 596 fewer cases of acute bronchitis annually in California.

Natural gas, a fossil fuel, is currently one of California’s primary energy sources, used to fuel power plants and industrial processes, heat buildings, and power appliances. The state is set to implement recent legislation calling for 100-percent carbon-free electricity, but there’s no current statewide policy to address the gas burned inside homes and commercial buildings.

Considering how severe the respiratory effects of COVID-19 can be, indoor air quality is more important than ever. People who have the ability to do so might want to switch to electric appliances as soon as possible, and investigate other potential sources of indoor air pollution in their homes like mold, scented candles, and formaldehyde off-gassed by furniture, paint, and textiles.