While you likely already know what not to do when the air quality is bad outside (no marathon training today), you may not be aware of the major no-no indoor activities to avoid when the air quality near you is in the red. International mold expert and speaker for the Indoor Air Quality Association, Michael Rubino, wants you to think of it this way: Each breath is either an opportunity to inhale pollutants or to inhale the cleanest air possible. And inside your own home, the choice is yours. According to Rubino, the best way to ensure air quality is good inside even if it’s bad outside is to first “develop a routine cleaning regimen to remove dust, allergens, toxins, and other indoor pathogens.” This can include keeping doors and windows closed when you know the air quality is bad outside. He also advises people to purchase a “good air purifier” that removes as small of a particle as possible and as efficiently as possible. And once those measures are in place? Here are five activities not to do at home to ensure your indoor air quality stays as safe as possible, even on a code red day. The same goes for space heaters. William J. Calhoun, MD, professor of medicine and vice-chair of the department of medicine at the University of Texas Medical Branch in Galveston, shared on WebMd that those tiny heaters can “release gases and particulates into the air.” RELATED: 5 Common Activities That Could Be Affecting the Air Quality Inside Your Home “The worst activity someone can do is exercise because it will increase the amount of exposure to chemicals and toxins that each individual has by up to a factor of 10, due to blood flow and respiration, which will only increase underlying exposures,” Richard Firshein, MD, a leading expert in integrative and precision-based medicine and founder of Firshein Center, shares. Jennie Bergman, the senior product manager, indoor environmental quality at Trane Technologies, agrees: “When contaminant levels are high, effects from exposure have the potential to show up immediately such as irritation of the eyes, nose, and throat; headaches; dizziness; and fatigue.” Thus, she says, “avoid activities that aggravate lung exposure to the contaminants, such as strenuous workouts and deep breathing exercises.” “Secondhand smoke is a serious health hazard causing more than 41,000 deaths per year,” the American Lung Association shares on its site. “It can cause or exacerbate a wide range of adverse health effects, including lung cancer, respiratory infections, and asthma.” This goes for e-cigarettes, too. “The use of e-cigs in indoor environments leads to high levels of fine and ultrafine particles similar to tobacco cigarettes,” researchers from the University of California shared in a 2020 study published in the Annual Review of Public Health. “Concentrations of chemical compounds in e-cig aerosols are generally lower than those in t-cig smoke, but a substantial amount of vaporized propylene glycol, vegetable glycerin, nicotine, and toxic substances, such as aldehydes and heavy metals, has been reported.” “Consumers should also avoid burning incense, candles,” says Lauren Wroblewski, senior consumer scientist at Seventh Generation, as these too could further spread pollutants. One study by researchers at the University of Copenhagen even found that particles released while burning candles could be as harmful to mice as diesel fumes. And sorry, but doing your nails is off-limits. As the Environmental Working Group explains, both nail polish and nail polish remover can contain Volatile Organic Compounds (VOCs) and could be harmful to your health. And remember that whole part about avoiding strenuous exercise? That includes cleaning as well, according to Wroblewski, as “your breathing is heightened during this activity.” RELATED: 10 Ways to Clean Smarter, Not Harder