When spring arrives, it’s a joy to open your windows and feel the fresh air. All too soon it will be summer and we’ll shut ourselves in again.
This ritual raises a question: Which is healthier — outdoor air or indoor air?
They’re related, of course. The air inside our homes originates from outside and can carry pollen or pollutants, such as those produced by combustion engines. Indoor sources might add to the mix with tobacco smoke, cooking, mold spores, dust and pet dander.
A tightly sealed home may allow this mix of particulate matter to become more concentrated inside than out.
For good health outcomes, “The key is to catch small particles,” says Stuart Batterman, an environmental health scientist at the University of Michigan’s School of Public Health.
Particles that are 2.5 millimeters or smaller — called fine particles, particulate matter 2.5 or PM2.5 — are small enough to travel deep into the lungs and sometimes cross into the bloodstream. Fine particles are regulated by the Environmental Protection Agency because they can cause health problems.
High particulate matter may be associated with serious outcomes, such as asthma attacks, heart attacks and premature deaths in people with heart or lung disease. Those affected may experience airway irritation, difficulty breathing and coughing.
The most vulnerable are those with asthma, particularly children because their airways are smaller, and elderly people who have respiratory conditions, such as chronic obstructive pulmonary disease or emphysema, or heart disease.
The first things you should do is try to remove the source of irritants, says Brian Christman, a pulmonologist and spokesman for the American Lung Association.
While air filters can be helpful, says Christman, who also is chief of medicine at Veterans Affairs’ Tennessee Valley Health Care System in Nashville, “they’re about number four or five on the list of things you can do about air quality.”
“If you’re allergic to cats, and have five cats at home, an air filter won’t help,” he says.
Short of getting rid of pets, you can keep them out of your bedroom. If mold is a problem, you’d want to dry out areas of dampness — whether that means fixing leaks or seepage or using an exhaust fan when you shower.
Use the exhaust fan over your stove when you’re cooking with high heat, such as grilling or stir-frying. Reducing the humidity of your home makes it less friendly for mold and dust mites. Specialized pillow and mattress covers can reduce dust mite exposure.
Christman also suggests avoiding harsh cleaners such as ammonia and bleach. “Those things are hard on your airways, particularly if you have sensitive airways,” he says. Stick to more natural cleaners such as vinegar and baking soda.
After you’ve managed source control, a good air cleaner may help filter out what’s left.
Air cleaners can remove particulate matter from the air inside your home. There are two basic setups: a portable appliance or adapting a house- or building-wide HVAC system. The stand-alone appliances, also called air purifiers, circulate the air in a room and trap particles. If you have a forced air system of heating and cooling, that system does the same thing for all your rooms, and you can upgrade the system’s filter to improve particle removal.
A 2012 study tested portable air cleaners in low-income households of children with asthma. Air cleaners, when used in the children’s bedroom, reduced particulate matter by an average of 50 percent. But families didn’t use the devices consistently.
Batterman, who co-wrote the study, says the portable air cleaners do produce some noise and people who use them do need to change the filters. “They do a reasonable job for a small area,” he says, such as a bedroom.
Those with forced air should take advantage of that system to clean the air throughout the house, Batterman says. You already have a filter; for cleaner air, you need to upgrade it to better catch small particles. And you need to change it regularly — every three months is a common recommendation.
The cheapest filters are worthless for catching particles, Batterman says. He recommends a pleated filter with a Minimum Efficiency Reporting Value (MERV) rating of 13 or higher (so does the EPA). The MERV 13 filters cost about $15 to $20.
The filter works whenever the system’s fan is running and the windows are closed. That means during heating or air-conditioning season; or you can turn on fan mode. Newer thermostats have a mode that cycles the fan on and off, so you get the benefits of filtering without running the system constantly.
“If you have a child with asthma or allergies, it’s quite effective,” Batterman says. And if you avoid one emergency room visit or a missed work day, then the more expensive filter has paid for itself.
A couple of things to watch out for: Don’t use air filters that have an electrical field. Called air ionizers or electronic filters, these create ozone, which is harmful for health. (Slightly off topic, but another invisible health hazard is radon. It’s best to test your home.)
Specific air-quality problems might provide additional reasons for filtering your home’s air, such as wildfires. Air quality trouble spots can be viewed daily at an EPA website, AirNow.gov.
But unless you have a health condition that requires you pay close attention to indoor air quality, you really don’t need an air filter.
Batterman says he’s not a proponent of super clean spaces. Christman says regular dirt and dust are not bad for you. There’s evidence that growing up in very clean environments is related to the rise in autoimmune and allergic disorders, although the precise culprits have not been identified.