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Whether you realize it or not, you’re probably sharing your home with unwanted roommates. Between the chemicals and other hazards found in common building materials, our homes can harbor some very unsavory, if quiet, houseguests.

This may not come as a surprise if you’re among the 1 in 4 Americans with some form of chemical sensitivity, or the 12.8 percent with multiple chemical sensitivities — a diagnosis that’s grown 300 percent more common in the past decade, according to a study by the Journal of Occupational and Environmental Medicine. But remodeling or building a healthier home requires knowing what materials to avoid or limit.

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“It’s pretty hard to get a completely safe product,” said Liz Harriman, deputy director of the Toxics Use Reduction Institute at the University of Massachusetts at Lowell. “But there are choices you can make that are better.”

As a general rule, using nails or screws is preferable to adhesive, and the more natural a material is, the better — unless it requires an unnatural finish or additive to make it useful. For example, linoleum and solid hardwood are two of the best flooring options when it comes to environmental health, said Bill Walsh, founder of the Healthy Building Network. Linoleum is made from natural linseed oil, making it a healthy and sustainable choice — when installed without adhesives. Similarly, Walsh recommends buying hardwood floors prefinished, so the chemical-laden protective layer gets applied in a contained, controlled environment at the factory, not in your living room. That’s because many floor finishes, such as polyurethane, contain volatile organic compounds, or VOCs. These foul-smelling chemicals take the form of a gas at room temperature.

“They’re often pretty powerful neurotoxins,” Harriman said. “They’ll affect your central nervous system. They can give you everything from a headache and respiratory problems to much more serious symptoms.”

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While paint used to be a notorious VOC offender, it’s now easy to find low- or no-VOC options from industry pioneer AFM SafeCoat and more mainstream competitors. Water-based p roducts are preferable to oil-based ones, Walsh said. He recommends paints certified GS-11 by Green Seal or, failing that, purchasing paint from The Home Depot. The home improvement giant no longer sells latex water-based wall paints with alkylphenol ethoxylates, chemicals banned from paint in Europe due to their endocrine-disrupting properties.

It’s not just paint and finishes spewing unstable molecules. “VOCs are found in a lot of things,” said Bob LaFond, owner of Boston Green Renovations and Terrene of New England, a green-building designer and supplier in Newton. “Cabinets are a big offender because they’re often made with particle board … and when you get them into your home, they really do smell.”

Cabinets and other composite-wood products can also contain formaldehyde, a carcinogen. “Formaldehyde is a very common substance; it’s found in wood. It’s a natural-occurring thing,” LaFond said, but too much of it and certain types can be harmful, particularly urea-formaldehyde. Choose solid-wood cabinets whenever possible, Walsh said, or cabinets sold as NAF (no added formaldehyde). Because it requires fewer binding agents, plywood is generally preferable to particle board, medium-density fiberboard, or oriented-strand board.

While granite and other stone countertops don’t pose much risk by themselves, the penetrating sealants they require do. “The real durable sealants used on countertops and on floors have an epoxy base, which is a highly toxic endocrine disrupting chemical, and there are no drop-in alternatives for those at this point,” Walsh said. For that reason, he said, it’s preferable to avoid a sealant-dependent material; he recommends a solid-surface (Corian, for example) or quartz counters.

Spray foam insulation is another big concern, Walsh said. Even a small exposure to the isocyanates that mix with the blowing agents can give you asthma, he said. “You’re basically doing chemistry on the house; you’re mixing compounds.”

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Fiberglass batting used to present its own problems, but as of 2015, “no insulation manufactured in the US uses formaldehyde as a binder anymore,” Walsh said, making the cotton candy-style fiberglass insulation a safer choice.

Carpet and upholstered furniture have historically been problematic because of flame retardants and stain repellents; the latter use a class of chemicals called PFAS, which may ring a bell if you’ve seen the new film “Dark Waters,” which is about a lawsuit against DuPont over pollution. “They work really well, but eventually they all break down into these chemicals, per- and poly-fluorinated substances, which never go away in the environment and cause problems with endocrine systems,” Harriman said.

Carpet can offer refuge to dust mites, mold spores, and other particulates as time goes on.
Carpet can offer refuge to dust mites, mold spores, and other particulates as time goes on. REDPIXEL - stock.adobe.com

Carpet can also contain toxic coal fly ash or polyurethane backings, but there are natural options available if you want something soft underfoot. “If you’re making a choice about carpet, use wool,” said LaFond. “It’s about the greenest thing you can use, and it’s incredibly durable ... There are wool-composite padding materials that are not toxic.”

Walsh recommends against vinyl flooring for several reasons — including the toxic production and waste cycles associated with polyvinyl chloride, but also the phthalate plasticizers typically added to make vinyl more supple. Engineered-wood floors and laminates without formaldehyde binders are a better choice if linoleum or solid wood is out of the question, he said.

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For a low-VOC floor finish, LaFond recommends a product called PolyWhey from Vermont Natural Coatings, which uses whey left over from cheese production. “It’s incredibly durable and much lower in VOCs,” LaFond said.

In 2016, Walsh’s organization debuted HomeFree, an initiative that aims to accelerate the use of healthy building materials in affordable housing. To that end, HomeFree developed a series of red-to-green “stop light” charts that rank bad and better choices for common building materials like flooring, paint, and composite wood.

HomeFree offers broad category recommendations, because “products vary so widely in how they’re manufactured,” Walsh said. “Literally the same type of carpet or same type of ceiling tile can have different contents based on which factory it comes out of.”

Another complexity is when what sounds like a healthy choice for the planet presents problems for your own health. Products made from recycled vinyl, for instance, would seem a slightly better choice for the environment, but Walsh said such materials often contain toxic chemicals the industry has since phased out. Some ceramic tiles, meanwhile, contain recycled cathode-ray tubes from old televisions, which often contain lead. HomeFree suggests choosing unglazed tiles or tiles made in the United States, which typically have a lead-free glaze.

And not to totally freak you out, but children are especially vulnerable to chemical exposure, Harriman said — and more likely to be spending time on that carpet or recycled-vinyl floor. “Their systems are developing. They’re smaller and consume more air and water per kilogram of body weight than an adult would,” she said.

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When it comes to your health, some of the most important building materials in the home are range hoods, bathroom exhaust fans, and home ventilation systems, said Bill Hayward, founder of the Hayward Score, which helps builders and consumers assess and improve the air quality and environmental health of their homes.

Hayward, the chief executive of California-based Hayward Lumber, became interested in home health after he and his wife purchased a newer house in 2008 and grew sick soon after moving in — sneezing, coughing, and feeling exhausted. “I at one point thought I had a brain injury, and I needed to sell the company,” he said, and their 6-month-old stopped growing. It turned out that mold in the home’s crawl space was permeating the indoor air, making all of them ill.

That nightmare experience prompted Hayward to study building health. He and a team set about designing a scoring system that could accurately assess a home’s potential for health issues based on certain conditions and the behaviors of its occupants — which, he hoped, could nudge builders to create healthier homes and consumers to make simple changes. They’ve since scored about 60,000 homes, tracking 23 self-reported medical symptoms.

“People can do a whole lot just by changing their habits,” Hayward said, whether it’s taking their shoes off when entering the home or running the range hood when they’re cooking. Preparing a large meal can release enough particulates to temporarily make your kitchen’s air quality worse than that of Delhi — one of the most polluted cities on Earth. But one study by Berkeley Lab found that a range hood, if switched on, can exhaust 50 percent to 70 percent of cooking particulates from a stove’s back burner.

Indoor air flow is an often overlooked facet of home health, Hayward said. When we heat our homes, the warm air rises, creating an air current. “It’s literally pushing to escape out the upper half of the house, and it’s sucking in like a vacuum through the lower extremities of the house,” Hayward said — especially through our basements and garages, damp places that may host unseen mold growth, but also our fuel oil, pesticides, paint cans, and other harmful chemicals.

The Environmental Protection Agency estimates that the air inside our homes is 2 to 5 times more contaminated than the outdoors — and we spend 90 percent of our time inside. The solution, Hayward said, is to ventilate the home in an intentional way. For example, a heat recovery ventilator will suck humid air out of the bathrooms and kitchen, filter it, and then return fresh air to bedrooms and living spaces. A cheaper, low-tech solution is to simply crack one window at the bottom of the house and another at the top — “just enough so you feel it on the back of your hand but it’s not a draft,” Hayward said. “Better it’s coming in through the edge of the window as opposed to through the wall or the dark undercarriage of the house,” where prolonged moisture may be creating a biology experiment.

Meanwhile, the environmental health risks of carpeting don’t end with chemical stain repellents and formaldehyde foam underlayment. Carpet can offer refuge to dust mites, mold spores, and other particulates as time goes on. “We see symptom counts increase 60 to 75 percent when your carpet gets up over 15 to 16 years of age,” Hayward said.

Grosser still . . . “When you remove old carpet, it often weighs close to 200 percent of its original weight,” he added.

That’s one roommate you’ll be glad to see go.


Jon Gorey blogs about homes at HouseandHammer.com. Send comments to jongorey@gmail.com. Follow him on Twitter @jongorey. Get more home improvement advice at realestate.boston.com.