The 4 worst enemies to breathing good air? Your walls.

The breath you just took is full of history.

Two millennia ago, Julius Caesar drew his final breath before dying at the hands of his assassins. Odds are that at least one of the molecules in that breath is in your lungs right now. It makes no difference if you’re in Rome, Japan, Argentina or even the North Pole – the air had plenty of time to disperse, and nothing was stopping it.  

That’s why humans burned fossil fuels for centuries before they faced the outdoor air pollution we have today. It takes constant, high-volume emissions to cause problems when there’s so much atmosphere to disperse into. But indoors, it’s a different story.

Buildings confine air in an unnatural way, preventing it from dissipating the way it does outdoors. The “history” in your home’s air is of nightly cooking fumes, months of furniture trapping dust, and mornings of your teenager spraying enough cologne to match his hormones. Without proper measures, indoor air can be up to eight times worse than outdoors—just like the consequences to your health.

What’s exactly in my air?

Air has lots of stuff in it. Molecules are really, really small, and it’s not just Caesar’s olive oil breath that’s been adding to it. Though without going too scientific, it’s mostly nitrogen (78%) and oxygen (21%). The nitrogen doesn’t do much, while the oxygen keeps you alive.

Next up (usually) is carbon dioxide, or CO2, varying between 0% and 6% since we breathe it out. Then there’s water vapor, followed by “noble” gases that get their name because they do almost nothing on a chemical level.

So far, none of these things hurt you. Some might think CO2 is bad since it seems like the “opposite” of oxygen, but studies show that breathing even extreme amounts of CO2 is perfectly safe. The culprits fall mainly into two distinct categories: “Volatile Organic Compounds” and “Particulate Matter.”

Volatile Organic Compounds: sneaky vapors that don’t play nice

“Hold on,” you might say. “Volatile sounds nasty, but organic? Isn’t organic good?”

Yes, and no. In scientific terms, “organic” just means “there’s carbon in it.” That’s important because carbon is like a molecular wild card: It can bond to many different chemicals, and a bunch of them at once, including other carbon atoms. That means organic molecules can be very long and complex, such as DNA. But it also means that they can do things they shouldn’t do if they end up in the wrong place.

That’s where the “volatile” part comes in. VOCs have a boiling point so low that they could evaporate even in your freezer, meaning it’s easy for them to turn into fumes and travel through the air. Breathe them in, and it’s like letting animals loose in a busy chef’s kitchen. Some aren’t harmful, like frogs hopping around his feet. Others are like monkeys, jumping around and actively interfering with important bodily processes. A few can cause permanent damage to your cells—dinosaurs that eat the chef.

In the short-term, VOCs can irritate your eyes and nose, give you headaches, make you tired yet also get in the way of sleep. In the long-term, they can damage your immune system, your kidneys, your liver, your brain, and can even increase your chances of getting cancer.

Unfortunately, many of the things that release VOCs are found indoors. Cleaning products are the worst as they carry some of the deadliest ones, like formaldehyde and ammonia. But VOCs also evaporate from materials in the building itself, like paint, adhesives and insulation. In fact, the effects of staying in a building with these issues for too long is so pronounced that it has a name: “Sick Building Syndrome.”

Particulate Matter: too small for comfort

Nature puts lots of stuff in the air, like pollen, molds, and dander. Since you started reading this, your own skin has dumped tens of thousands of particles into the air in the form of dead cells. Because of this, our bodies have natural defenses that keep them from hurting us, starting with your nose hairs and leading to a picky filtration system in your lungs.  

Occasionally, natural particles pass through these obstacles. But there’s a magic length—2.5 micrometers—where anything smaller can easily pass through these barriers and end up in your bloodstream. Nature makes such particles occasionally, but mankind makes them a lot. Burning things, whether it be oil, coal or wood, puts enormous amounts of “PM2.5s” into the air. Car exhaust, power plants and industrial complexes are some of the worst offenders.

Much of indoor PM2.5s come from the outdoors. But your home’s biggest source is your kitchen stove. We all know that burning a roast can fog up the room and set off the smoke alarm, but cooking releases plenty of particles even when it’s not so apparent. Candles, fireplaces and most anything that involves burning something releases PM2.5 particles.

That includes cigarettes, which is why the dangers of breathing PM2.5s are much the same as smoking: both immediate and long-term damage to your respiratory system and heightened chance of heart disease. Other symptoms resemble allergies, like irritation to your eyes, nose and throat. Anyone with sensitive respiratory systems, such as the young and elderly or anyone with asthma, is especially affected.

Other offenders

Not every indoor pollutant fits into the VOC or PM2.5 gang, though. Buildings have a way of trapping big clumps of natural pollutants, and even helping nature make more of them.

Dust is a big one. The cloth in your curtains and furniture collect lots of the stuff, which later falls off and fills the air nearby. Spore-spawning mold can grow in wood, and mites love a quiet shelter where they can breed and produce fecal matter that gets swept up into the air. While these particles are mostly too big to pose the dangers of PM2.5s, the unnaturally high concentrations in buildings isn’t exactly physician approved.

And you can’t talk about pollution without mentioning carbon monoxide, or CO. Thankfully there’s more awareness about CO than other indoor air concerns. While made of the same stuff as the mostly-harmless carbon dioxide (CO2), CO is much deadlier; too much can make you very sick or even kill you in a matter of minutes. It takes a lot, but given the dangers it’s imperative that we keep on the lookout for it.

Okay, so my air is bad. What do I do?

Before you think about solving the problem, know that the biggest harm comes from time. Just as smoking a single cigar won’t kill you, but living with a smoker might, air pollution does the most damage from prolonged exposure rather than individual times you breathe bleach fumes or smoke up the house cooking tacos.

That’s important because we already take steps to vent out extremely bad air. We turn on the fan when we bleach the bathroom floor, and generally open the window if there’s smoke or a bad smell. But you can breathe kind-of bad air every day without knowing it.  That’s where the change needs to happen.

Good habits, good air

Just by reading this article you’re likely to breathe a lot better. Being just a little cognizant of the things that pollute your air can lead you to do the little things that make a big difference.

When you use cleaning products, make sure to open your doors and windows before you start cleaning, and leave them open for 30 minutes afterward, even if there isn’t a strong smell. The same applies to cooking. If you have a hood over your stove, even better! Turn that sucker on before, during and after you cook, rather than waiting for the smoke detector to prompt you.

If you don’t dust regularly, start. Make sure to hit the spots you don’t normally see, like behind the television and under your furniture. Speaking of furniture, use a damp cloth to scrub the fabrics themselves. Wipe the ceiling, walls and floor on occasion, and if you have carpet, break out the Hoover. You certainly don’t have to do it every day or even every week, but do it long before it makes you sneeze.

Also, keep scented candles and oil diffusers for special occasions. Just because they’re good on the nose doesn’t make them good on the lungs. Air fresheners are just fine, but make sure they’re all natural.

Make the house do its part

Some changes take a bit more work up front, but can have huge, instant results.

Every once in a while, check your ventilation to make sure it’s working at 100%. The easiest way to do this is to take a piece of paper and hold it against the intake vent while the system is running. Let go. If the paper sticks, your vents are working great! If not, there’s likely a blockage or a leak that’s stopping you from getting fresh air. See if your filter needs replacing, and if not, it’s time to call a specialist.

Replacing furniture’s not the easiest thing on your wallet or your back. But the wood and foam in cheaper furniture can emit VOCs, even the cancer-causing formaldehyde if it’s more than ten years old (owing to a flame retardant that has since been banned). Look for fixtures made of solid wood, not pressed or particle board, and go for upholstery stuffed with natural fibers like linen and wool instead of polyester foam.

Your house’s humidity should also stay around 40-50%. It’s a healthy range for not just humans, but the building itself. High humidity is ideal for molds, which release tons of spores into the air. Running a dehumidifier during rainy months can solve this problem. And while humidity is usually associated with higher temperatures, letting the house get too cold actually worsens the problem since cold air can’t absorb as much water as warm air.

It may also be worth hiring a professional to work on optimizing your home’s HVAC system. An efficient system can make sure your air is recycled regularly and the humidity is well-balanced. This can be a tad pricey, but can also make your home more comfortable and lower your energy bills. And seeing as moisture is the number one cause of damage, it might pay for itself quicker than you think.

Bring in the tools

Even making half of those changes can make a big difference. But there’s still some things you just can’t do without help from a few gadgets.

Keeping an air purifier around is handy when opening the window isn’t a good idea, like if it’s cold out or if the air outdoors is more polluted than indoors on a given day. They come in a variety of sizes and price tags, so you can buy one to fit your situation. If your home is already well-ventilated, you probably don’t need something fancy. But if you’re going to be relying on it a lot, best to spend a little extra.

But the biggest obstacle to fighting indoor air pollution is that it’s invisible, and that’s where a small purchase can make the biggest difference. A good indoor air quality monitor can tell you exactly when you’ve got problems with VOCs, PM2.5s, carbon dioxide and monoxide, and even humidity and temperature. The best ones can track your quality over time.

This information is useful across the board. It helps build habits, because you can see the exact change in air quality when you run your stove hood for a bit longer or crack the window more often. Moreover, it means you’ll know when something starts polluting your air that you don’t know about, like if an adjacent apartment is doing a big painting project, or if your daughter’s freshly-dyed hair is letting off more fumes than you thought. A monitor lets you nip every air quality problem in the bud, potentially saving you months of breathing bad air.

Fixing air quality isn’t just a pain in the gas

A lot of these steps might seem like overkill. After all, we’ve gone without worrying about air quality for a while without problems, right?

But the problems were there; we just didn’t know where to point the fingers. A 2012 study estimated that indoor air pollution causes roughly as much loss of life as automobile accidents. The difference is that car crashes are the least subtle things in the world, whereas long-term health conditions creep up very slowly.

Yet cleaning your air doesn’t have to be about fear of getting cancer someday. Better air makes it easier for your body to sleep, concentrate on tasks, and fight off diseases like the cold and flu. Like eating well, it’ll make you feel happier and more energetic.

That, and there’s no need to go all in from the start. You’ll start to feel benefits just by opening your windows more and cleaning out your filters. If you do, then you can think about replacing your furniture or picking up an air quality monitor. Do it entirely on your terms; either way, the difference will be huge.