Illustration of a yellow house on a blue background

Credit: Illustration by Paul Garland

Could your house make you sick?

Johns Hopkins experts weigh in on pressing questions about health and safety indoors

To describe something as risk-free and secure, there's an old saying: "As safe as houses."

Our houses were certainly seen as refuges during pandemic lockdowns. Now, amid the ongoing trend of working remotely, we're spending more time than ever in our homes. Americans, on average, spend approximately 90% of their lives indoors, according to the Environmental Protection Agency.

But how safe are our houses? Outdoor air quality has been monitored and regulated for decades, with air pollution information and alerts now part of weather reports. But what about indoor air—the stuff we spend the bulk of our time breathing? The EPA has found that the concentrations of some pollutants are often two to five times higher than typical outdoor concentrations.

There are currently no standards for indoor air quality, and many of its potential risks remain little understood. Witness the news splash (and caveats) greeting recent research on the potential health hazards of gas stoves. And domicile dangers long uncovered, such as radon, remain a threat not fully appreciated.

Johns Hopkins researchers are working to fill the large gaps in our knowledge about how indoor activities—cooking, cleaning, showering— along with allergens such as dust and mold, impact human health. We asked some Hopkins experts to weigh in on various household hazards and offer mitigation advice where appropriate. With some prudent precautions, they say, home can be a safe haven.

Tales of the Tap

The 1974 Safe Drinking Water Act (amended in 1986 and 1996) empowers the EPA to regulate the nation's water supply, setting limits on nearly 90 potential contaminants. Natalie Exum, BSPH '16 (PhD), an assistant scientist in the Department of Environmental Health and Engineering, says the act is one of the most effective pieces of environmental legislation we have.

Still, all might not be right with what flows from your faucet or showerhead.

The country grapples with larger infrastructure needs, such as replacing old pipes that could leach dangerous contaminates and bringing cleaner water to rural areas. In the past decade, the troubled water systems in Flint, Michigan, and Jackson, Mississippi, have resulted in an ongoing public health crisis and national wakeup call.

Inside our own homes, pipes can be sources of harmful chemicals, including lead that can leach out of lead-soldered fittings in older homes. Household pipes can also harbor biofilms, colonies of microorganisms that can include Legionella bacteria, which causes the pneumonia-like illness Legionnaires' disease. And if you are among the more than 43 million Americans using water from a private well for drinking and bathing, you face all these issues while being largely on your own to determine whether the water you pump from the ground is safe.

Expert tip: Consumers should have a well water test at least annually and be alert for any changes in its color, smell, or taste, Exum says. She adds that county health departments are usually the best resource for information on potential localized water hazards and testing resources.

"For most [PFAS] we just have zero understanding of their health impacts and how they mix with one another is of huge concern."
Carsten Prasse
Assistant professor of environmental health and engineering

Meanwhile, researchers on the frontiers of water-safety science are examining the risks of PFAS, an acronym for per- and polyfluoroalkyl substances, dubbed forever chemicals because of their resistance to breaking down in the environment. Traces of one or more of these chemicals are now found in nearly half the country's tap water, according to a recent study by the U.S. Geological Survey. They have been linked to reproductive and immune system harm, cancer, and other diseases. "For most of them we just have zero understanding of their health impacts and how they mix with one another is of huge concern," says Carsten Prasse, an assistant professor of environmental health and engineering who studies water contamination. The EPA recently drafted legislation to regulate six PFAS in drinking water. It's a start, Prasse says.

Expert tips: A plethora of home water-filtering systems are available, ranging from $30 pitchers to sophisticated whole-house filters costing thousands. Many of these pitcher-based filters effectively remove heavy metals such as lead and cadmium, Exum says. The most established method for removing PFAS is with a reverse osmosis filter, often mounted under sinks. To help you sort through the manufacturer's claims, the National Sanitation Foundation tests and certifies filter performance to various standards.

Public water system administrations release annual Consumer Confidence Reports (mailed with bills and available online) listing the amounts of various contaminants found in their water. The EPA's website provides resources for consumers looking to test their own water, including links to government-certified labs in their state.

"The main exposure to some harmful compounds is through showering because, in a hot shower, you form aerosols and you can inhale them, in addition to skin exposure."
Carsten Prasse
Assistant professor of environmental health and engineering

Bathing or showering with tap water can present another hazard. "The main exposure to some harmful compounds is through showering because, in a hot shower, you form aerosols and you can inhale them, in addition to skin exposure," Prasse says. One such group of compounds is trihalomethanes, formed when the disinfectants that water systems use, such as chlorine, interact with naturally occurring organic materials. These "disinfectant byproducts" are widespread, and while more research is needed, at high levels they are associated with long-term cancer risks, Prasse says. Hot tubs and humidifiers can also bring aerosol risks.

Expert tips: Activated carbon filters are most effective in removing harmful organic compounds in water. And moving water is generally safer water. When water sits in pipes for extended periods, such as when you're away on vacation, any lead in your plumbing has time to leach out and biofilm pathogens are more likely to be present. One simple precaution is to let your water run a few minutes when it hasn't been used in a while to flush out any harmful buildups. "You want really to turn over the water in your whole house if you've been away from home for an extended period of time to ensure that you're getting fresh chlorinated water in there again," Exum says. Ensuring that your hot water heater is set to at least 120 degrees Fahrenheit can also help.

Radon and Me

Radon is a stealthy household toxin. This colorless, odorless, radioactive elemental gas emerges from the ground (the byproduct of the natural decay of certain types of rock) and is a known carcinogen that can get trapped in your lungs. It's the second leading cause of lung cancer after smoking and is associated with an estimated 21,000 deaths a year.

Outside, it harmlessly dissipates into the atmosphere. However, if it comes out of the ground beneath a house or other structure, it can accumulate to dangerous levels. The EPA created maps in the 1990s indicating areas of the country at the greatest risk for elevated indoor radon levels. But Paul Locke, SPH '98 (DrPH), a professor in the Department of Environmental Health and Engineering, advises against relying solely on these maps to assess your danger.

"If your house is in an area where they show low radon potential, you still could be at risk," he says.

Expert tip: Basic radon test kits—available at hardware stores and online—involve small devices that you position in the lowest area of your living space. After a specified period, you seal it up and send it to a lab for evaluation. The combined cost of the kit and lab processing is around $30. If results show radon is not present at hazardous levels, you generally don't need to test again unless you make home renovations.

And if unhealthy levels of radon are found?

"The basic mantra for radon is test, evaluate, and fix," Locke says. "There's almost no home or building I've ever heard of that can't be fixed." You (or your landlord), Locke says, will need to call in a specialist to design and implement a radon remediation system, which usually involves changing the pressure dynamics beneath the foundation so that the radon vents up a pipe through the roof instead of seeping into living spaces. After remediation, a radon gas detector is recommended.

Fungus Among Us

Mold can be a lifesaver, such as the fungus-derived antibiotic penicillin. But when mold proliferates in your home, it can produce a bloom of allergens and irritants. Sensitivity to the fungus varies from person to person and can be worse for those with asthma. Just breathing in or touching mold spores can cause nasal congestion, red eyes, and wheezing. "In extreme cases with what we call black mold, you can have flu-like symptoms, diarrhea, headaches, and severe respiratory distress," says Marsha Wills-Karp, a professor and chair of the Department of Environmental Health and Engineering. "It can be quite bad, and younger children are more susceptible than adults."

Illustration of a blue hand holding a petri dish with a house image

Image credit: Illustration by Paul Garland

Molds come in a variety of colors and growth patterns, but what they all have in common is a need for moisture. Stray mold spores float all around us, and when they encounter a damp place with a food supply (any organic material, such as wood or paper), they can begin to colonize. Outbreaks can follow plumbing leaks or water intrusion in roofs, walls, or floors when it rains. Where humidity is high, condensation on pipes or windows can also be a source of moisture. When mold can't be seen, such as behind walls, its musty smell can alert you to its presence.

Expert tip: "Basements are places you find [mold] most, and it's a good idea to be regularly evaluating your basement, particularly after a heavy rain," Wills-Karp says. "Any water needs to be eliminated as soon as possible. Put fans on and take up any carpets and fabrics and make sure it all gets dry." Dehumidifiers can also help.

Small moldy areas can be cleaned with a bleach solution, and it's a good idea to wear an N95 mask, goggles, and gloves when doing so. A mold remediation specialist might be needed for larger blooms or those in hard-to-reach places; the Centers for Disease Control and Prevention recommends using a professional to clean moldy areas over 10 square feet.

Eight-Legged Bedmates

For most people, dust mites are more gross than troublesome. Who wants to think about millions of eight-legged creatures fornicating, defecating, and dying in our mattresses and bedding? But chances are you'll sleep with them tonight. These microscopic arthropods (related to spiders and ticks) don't bite, burrow into flesh, or sting but rather live on cast-off flakes of our dead skin and thrive where the humidity is over 50%. The American Lung Association estimates that dust mites can be found in four out of five homes.

"Dust mites are... not going to kill you, but they can cause a lot of illness. It's actually their fecal material that we're allergic to, causing red eyes, sneezing, coughing, and shortness of breath."
Marsha Wills-Karp
Chair of the Department of Environmental Health and Engineering

"Dust mites are one of the primary allergens, particularly in people who have asthma," Wills-Karp says. "They're not going to kill you, but they can cause a lot of illness. It's actually their fecal material that we're allergic to, causing red eyes, sneezing, coughing, and shortness of breath."

They're most frequently found in beds because that's where we spend around eight hours a day under the covers creating the warm humid conditions dust mites prefer while shedding plenty of dead skin flakes for them to feast on. They can also live in furniture, carpets, and some clothing, particularly items that are not washed frequently, such as coats. "They're sort of ubiquitous and not really a sign of a lack of cleanliness," Wills-Karp says.

Expert tip: Dust mites can be kept at bay in our beds by using special mattress covers and pillowcases woven to be impervious to dust mites. Blankets and other bedding should be frequently washed in hot water, Wills-Karp says.

You Smell That?

You know that heady, plasticky aroma dubbed new car smell? What your nose is actually detecting is called off-gassing: when new plastics, vinyl, adhesives, paints, synthetic fabrics, and other manufactured materials emit gaseous volatile organic compounds (VOCs), such as benzene, styrene, and formaldehyde, trapped within them during manufacturing. Off-gassing happens in the home as well, from furniture, paints, carpets and flooring, and mattresses.

"Generally, if you smell it and it smells a little chemically, it's not good for you."
Peter DeCarlo
Associate professor of environmental health and engineering

"Generally, if you smell it and it smells a little chemically, it's not good for you," says Peter DeCarlo, an associate professor of environmental health and engineering. Sensitivity to off-gassing varies, and short-term effects include headaches, hoarseness, and eye irritation. Less is known about the potential long-term health risks of off-gassed VOCs. While many are known to be carcinogenic, more research is needed to understand what concentrations are dangerous and how they might mix with one another. Most household air filters won't remove them.

Governments and industry are starting to pay attention. The EPA has launched ongoing efforts to regulate formaldehyde emissions from engineered wood products, and California's Proposition 65 consumer information law mandates that household goods that may off-gas carry warning labels. Meanwhile, the flat-pack furniture giant Ikea has phased out formaldehyde in its paints and adhesives.

Expert tip: Low- or no-VOC house paints are now available at hardware stores, and third-party certifiers, such as Made Safe, evaluate consumer goods and label those that produce low or no emissions.

"I prefer natural materials because they're more sustainable," DeCarlo says. "Solid wood is just better than particle board because you don't have all the glue holding the pieces together." Off-gassing dissipates over time, usually within a few weeks or months.

Hot Topic

Gas ranges went from mundane kitchen appliance to political lightning rod seemingly overnight after research emerged last year from Stanford University highlighting their contributions to both indoor air pollution and global warming. Hopkins researchers have also been exploring this topic, including a 2008 study showing that gas stove emissions aggravate asthma symptoms in children. Ideological squabbling aside, some 47 million U.S. households contain gas stoves, so what happens when we cook with it?

"If you burn natural gas to make food, along with that blue flame comes things like carbon monoxide, carbon dioxide, and nitrogen oxides," DeCarlo says. "Also, a little bit of leakage of methane, which is really more of a climate issue."

"A lot of people have vents over their cooking surface that may actually just blow air right back into the room."
Peter DeCarlo
Associate professor of environmental health and engineering

That leakage can add up, with estimates suggesting the nation's gas stoves have the annual climate change impact of 500,000 cars. The blue flames also emit harmful particulates and the noxious pollutant benzene and nitrogen dioxide. New research suggests that gas stove usage might be responsible for over 12% of childhood asthma cases. And in less time than it takes to boil a pot of spaghetti, a poorly vented kitchen can blow past the EPA's standards for outdoor air quality. Nitrogen dioxide is particularly harmful. "It is a respiratory irritant that can lead to a host of respiratory issues," DeCarlos says. "Its concentration and buildup are what modulates what the ultimate health impact is."

Expert tip: The ready solution to the emissions released from a gas stove is to always use the exhaust hood when cooking—providing it actually vents outside. "A lot of people have vents over their cooking surface that may actually just blow air right back into the room," DeCarlos says. People in this situation may have to use an open window and a fan to help ventilate the room. Tabletop appliances, such an electric kettle for boiling water, can reduce your need to always fire up your gas stove. Dedicated cooks who love the power and speed of gas cooking should know the latest electric induction stoves are nothing like the glowing-coil electric ranges of old. Still, switching is expensive. The High-Efficiency Electric Home Rebate Program within last year's Inflation Reduction Act can help, as it provides needs-based rebates of up to $840 toward the purchase of an electric stove.

Oh, and while gas stoves produce some carbon monoxide, deadly levels of this odorless gas in the home are more likely to come from other flames, such as gas furnaces, water heaters, and other appliances. "When these are not working properly or optimally, they can produce high concentrations of carbon monoxide from poor combustion," DeCarlo says.

The U.S. Consumer Product Safety Commission recommends that every household have a carbon monoxide alarm. Combo alarms monitoring for smoke and carbon monoxide are available so that you have only one device chirping at you when it's time for a battery change.

Brennen Jensen is a senior staff writer forĀ Johns Hopkins Magazine.