While you may blame outdoor air for carrying loads of potential allergens and pollutants, it turns out indoor air can actually be more harmful for your health than its outdoor counterpart. Because the air is so concentrated, volatile chemicals and pollutants can build up inside the home.
 
"People certainly do have misconceptions about indoor air. It can be dangerous and there are all kinds of things that can have adverse [health] affects," says David Carpenter, MD, professor of environmental health and toxicity at the University of New York at Albany. Luckily, most of these worries can be eased by something as simple as opening your window.

"In general, outdoor air is much safer than indoor air. The concentration in almost every chemical is greater in indoor air than in outdoor air," he says. While opening the windows is the best fix for circulating and cleaning indoor air, if you live in an area with bad air quality or if you're susceptible to allergies, use these tips below to keep your home safe. 
 
Indoor Air Pollutants and How to Avoid Them
Tobacco: "The chemicals that are in tobacco smoke are documented to be more dangerous for the secondhand smoker than the smoker themselves," Dr. Carpenter says.
Fix It: If smoking cessation isn't an option, refrain from smoking in the house and keep all ashtrays outside.  
 
Volatile Compounds: There's the assumption that if you spray a cleaning agent or insecticide in a certain location, it stays there. But that's incorrect. "If you spray to kill the roaches and the ants and assume that you spray it under the kitchen sink and it stays there, it doesn't. You spray it and it goes into the air," Dr. Carpenter says. While these sprays are designed to disinfect, if they get into your lungs they break down your immune system and disrupt natural body functions like digestion and disease fighting. 
Fix It: When you spray, make sure to open the windows and let the room air out at least three hours after using chemicals. Only spray when children and the elderly will be out of the house for a couple hours because their immune systems are weaker, putting them at a higher risk than healthy adults. 
 
Carpets and Shower Curtains: A lot of household items like carpets and curtains come from the same source as the fuel for your car—petroleum. "So many of the articles in the household are gasoline-based, or made up of hydrocarbons. Hydrocarbons are not excessively toxic, but you don't want to breathe them over a long time," Dr. Carpenter says. That "new car" and "new carpet" smell? That's from the hydrocarbons. "[You] shouldn't panic about these things, but on the other hand it's always good to be aware of the fact that these cause headaches and impact brain function," he says. 
Fix It: Open newly purchased items in the garage and let them air out for a week before moving them into the house. Chances are, most things made from plastic or polyester are petroleum-based, so curtains, carpets, shower curtains, and anything plastic (unless it specifies non-petroleum) should be aired out.
 
Radon: Radon is a naturally occurring radioactive chemical that takes the form of a colorless, odorless gas. According to the EPA, radon is found in soil and typically moves up from the ground into the home through cracks and holes in the foundation. It gets trapped in the home and builds up. Long-term exposure to radon can cause lung cancer. One of the best ways to know if your indoor air is exposed is to do a home test kit.
Fix It: Thankfully, dispersing radon can be simple—just open the windows in each room every once in a while whenever possible and when someone is home. "People tend to always depend on air conditioning, but if it's not unbearably hot it's better to get air circulating between indoors and outdoors," Dr. Carpenter says. Air conditioning doesn't allow for the same exchange between fresh and stale air the way a window does, he says.
 
Paint: Everyone knows that fresh paint smell and here's the thing: It's not good for you, even in small quantities. Oil and even latex-based paints aren't the best to breathe in if you're living in tight quarters, so if you have to paint, try to arrange for a weekend away after painting to allow the house to air out, Dr. Carpenter says.
Fix It: Time paint jobs around a weekend trip. If you can't get away, try to schedule a trip for your kids and family members who are susceptible to respiratory or allergy problems. If that's not possible, make sure to keep the windows open to allow the house to air out. 
 
The Bottom Line:
In the same way there can be sick building syndrome," there can be "sick home syndrome," Dr. Carpenter says. "People don't realize that the indoor air in their home is making them not feel really healthy." In general, the older and draftier your home, the more it allows for fresh air to flow through. Because modern homes are so tightly insulated, they're more likely to result in "sick home syndrome" from lack of air circulation. The best way to "heal" your home: Open the windows!