Wood Guide
Real solid wood is getting harder to find in furniture, increasingly replaced by MDF, particleboard, and other engineered "woods," made with glues and covered in plastic veneers. This guide covers which versions are healthier and how to evaluate the variable parts of real solid wood: its stains and finishes, since even solid wood can carry solvent-based stains or lead paint in older pieces. The clearest things to avoid outright are thermofoil, melamine TFL, PVC laminate, and any vintage painted piece without confirmed lead testing. This guide is one of the rating systems behind the Interior Medicine Method.
By Dr. Meg Christensen | Physician-founder of Interior Medicine, a non-toxic home resource built on her background in medicine, biochemistry, epidemiology, and clinical research.
Published March 1, 2021 | Updated Sept 29, 2026
Wood Rating Scale
These scales are a summary of all the information below. They also keep me consistent and unbiased as I rate and rank products for their potential impact on your health, and they’re meant to organize the information in a straightforward way for you, too.
The scale captures a complete picture of wood’s potential impact on your health by considering the wood (or “wood”) itself, and how it was treated — that includes applied stains, finishes, paints, and veneers. Keep reading for the full breakdown on the reasoning behind it, and how to make smart decisions about wood in your home.
Wood Rating Scale
TIER 01
Healthiest
Description
Solid wood, unfinished or with natural finishes only
- Solid wood throughout the piece, either unfinished or treated only with plant oils (tung, linseed, hemp), hard wax oils, natural shellac, or wax, with no engineered wood anywhere, no film-forming finish (like polyurethane), no stain or paint
Look for
- "Solid wood" or "solid hardwood," often named by species ("solid oak," "solid walnut")
- "Raw," "unfinished," or "no finish"
- "Tung oil," "linseed oil," "hemp oil," "hard wax oil," or "natural shellac"
- Watch out for "solid engineered hardwood," which is not solid wood, it's a marketing term for a thin layer of real wood over a "wood" core
Ask the brand
- Is this solid wood throughout, or is any part engineered?
- Is there any stain, paint, or film-forming finish anywhere?
In practice
- Rare
- Mostly high-end natural brand craft furniture, some Amish makers, or sawmill-direct unfinished items
TIER 02
Healthy
Description
Solid wood with a disclosed low-VOC finish, or certified engineered wood
- Solid wood with a water-based, low- or zero-VOC stain or penetrating finish the brand names or clearly describes. No certification needed, since solid wood has no binders inside to off-gas
- No-added-formaldehyde engineered "wood" or veneer, or any film finish, with whole-product certification (GreenGuard GOLD or Indoor Advantage Gold)
Look for
- A named finish, or "water-based" plus "low-VOC" or "zero-VOC," on solid wood
- GreenGuard GOLD or Indoor Advantage Gold on the finished product (required for engineered wood)
Ask the brand
- What finish do you use, and is it low- or zero-VOC?
- Is any part engineered? If so, is the finished product certified?
In practice
- Health-focused brands and small makers who disclose their finishes
TIER 03
OK
Description
Film finishes, vague finish claims, or uncertified engineered wood
- Solid wood with a low-VOC water-based polyurethane, acrylic topcoat, or paint, without whole-product certification. Low-VOC, but it forms a plastic film
- Solid wood with a "non-toxic" or "eco-friendly" finish claim that doesn't name the finish type or VOC level
- No-added-formaldehyde engineered "wood" with a low-VOC finish, without whole-product certification, so it's up to you to trust the brand's binder claim
You'll see
- "Water-based polyurethane," "acrylic topcoat," or "low-VOC paint"
- "Non-toxic finish" with no details
- "CARB Phase 2 compliant" presented as a health claim (it's the US legal baseline)
Ask the brand
- Is the finish a film topcoat, or a stain or oil that soaks in? A penetrating finish moves solid wood to Tier 2.
- What binder bonds any engineered parts? A urea-formaldehyde or "I don't know" answer drops it to Tier 4.
In practice
- Common on mid-priced solid wood furniture sealed with water-based poly
TIER 04
Use Caution
Description
Standard wood with conventional surface treatments
- Standard "wood" with solvent-based finishes
- Solid wood with solvent-based finishes (lacquer, varnish, oil-based polyurethane)
- Solid wood with conventional latex paint or oil-based enamel paint (like alkyd paint)
- HPL (high-pressure laminate, the Formica-style hard surface) on a "wood" core
You'll see
- No disclosure of "wood" type, binder, or finish chemistry
- "Polyurethane" without a water-based qualifier, or "oil-based stain"
- "Conversion varnish" or "catalyzed finish"
- "HPL," "Formica," or "high-pressure laminate"
- "Alkyd" or "enamel paint"
Ask the brand
- What kind of "wood" is used and what adhesive or resin binder bonds it?
- Is the finish water-based or solvent-based?
- Is the surface real wood veneer or laminate?
In practice
- The default for most mass-market and mid-tier furniture, big-box flat-pack DIY pieces, kitchen cabinets, and factory-finished bedroom and office furniture
- HPL sits at the worse end of this tier and is borderline with Tier 5
TIER 05
Harmful
Description
Wood containing known harmful chemistry
- Plastic-surfaced "wood": melamine TFL (a core made with urea-formaldehyde and a formaldehyde-based surface applied), thermofoil (a thin vinyl layer heat-pressed onto MDF, common in low-cost cabinets), or PVC laminate
- Painted vintage wood with potential lead paint (pre-1978 US or imports without lead testing)
- Engineered wood with high formaldehyde-emitting binders, more common in some imports and resale
You'll see
- "Melamine," "TFL," "thermally fused laminate"
- "Thermofoil" (despite the name, it's vinyl, not foil)
- "PVC laminate" or "vinyl"
- Any plastic-feeling surface on a piece marketed as wood
- Chipped surfaces revealing pressboard underneath
- Vintage painted furniture without documented lead testing
Ask the brand
- Is the surface real wood veneer or plastic laminate? If laminate, what kind?
- For vintage items: has the paint been tested for lead?
In practice
- Common in low-cost flat-pack furniture, kids' furniture, office furniture, kitchen cabinets, and rental-grade pieces
HAZARD
Decoder
Prop 65
A Prop 65 warning on a wood product means the brand either knows a listed substance is present above a regulatory limit, or is labeling as a legal precaution. It measures whether your potential exposure meets a certain limit. Each chemical can look alarming on first glance, but there's more nuance to whether you need to worry. Read below to see what each chemical actually means and what to do about it.
The most common possibilities for a Prop 65 warning on wood are:
- Wood dust: solid wood furniture and unfinished wood products, listed for inhalation exposure during cutting, sanding, and manufacturing. The most common reason for warnings on otherwise clean solid wood pieces, including products with no other concerning chemistry.
- Formaldehyde: urea-formaldehyde and phenol-formaldehyde resin binders in plywood, MDF, particleboard, OSB, and most composite wood. The dominant trigger in engineered wood, off-gassing for years after manufacture.
- Toluene: solvent in oil-based stains, lacquers, polyurethane finishes, and some sealants.
- Crystalline silica (respirable): wood filler products, putties, and abrasive sanding products used in wood finishing. The exposure pathway is inhalation during sanding and manufacturing, so it's the workers making the product who are exposed, not you using the finished piece.
- Naphthalene: wood preservative in some treated wood products and older mothproofing for wood storage.
Prop 65 Wood
What should I do about a Prop 65 warning on wood?
Prop 65 warnings on wood are a mixed bag. Some flag exposures that happen during manufacturing, not during your use of the finished product. Others flag chemistry that continues to off-gas into your air for years after the piece arrives in your home.
Companies will essentially never tell you exactly which chemical is present in their product to warrant a Prop 65 label, but your response can be the same no matter what: don’t buy it and choose one without a Prop 65, or ventilate daily and use an air purifier that is capable of capturing VOCs.
If you do get information, the chemical possibilities sort into two groups— ones that deserve your attention and ones that don’t:
Not worth your worry: These come down to exposures that happen during manufacturing, when workers breathe in dust or fumes during cutting, sanding, or finishing. Different exposure route, different dose, and a totally different risk profile than living with the finished piece.
Wood dust: A known human carcinogen by inhalation, linked to cancers of the nose, throat, and sinuses with regular exposure to significant amounts. The exposure that matters is during cutting, sanding, and manufacturing, which means it's the workers making the furniture who face the relevant exposure, not you using the finished piece. This is why solid wood furniture with no other concerning chemistry, including organic certified pieces and natural-brand craft furniture, still routinely carries a Prop 65 sticker. The warning is honest, the listing is real, but the consumer exposure pathway in normal use is essentially zero once the wood is cleaned and assembled.
Crystalline silica: A known human carcinogen and the cause of silicosis, both by inhalation. Found in wood filler products, putties, and abrasive sanding products used in wood finishing. The exposure pathway is inhalation during sanding and manufacturing, so it's the workers making the product who are exposed, not you using the finished piece.
Worth your attention: These chemicals can off-gas from the wood or its finish for months to years after manufacture, with the rate sped up by heat and humidity. Ventilate well, allow off-gassing time before heavy use, and where the chemistry is the most hazardous, choose a different product category.
Formaldehyde: A known human carcinogen linked to nasopharyngeal cancer and leukemia, and a respiratory irritant that can trigger asthma. The dominant trigger for Prop 65 stickers on engineered wood. Used in urea-formaldehyde and phenol-formaldehyde resin binders that bond plywood, MDF, particleboard, and OSB. Off-gassing continues from the glue line for months to years after manufacture. If a product carries both a Prop 65 sticker for formaldehyde and a GreenGuard GOLD or Indoor Advantage Gold certification, the sticker is usually applied out of legal caution rather than confirmed exposure, since those certifications verify total emissions from the finished product at levels below most regulatory thresholds.
Toluene: A neurotoxin that affects the central nervous system, with developmental effects shown in pregnancy. Used as a solvent in oil-based stains, lacquers, polyurethane finishes, and some sealants. The strongest exposure is in the first few weeks after application; ventilation and off-gassing time help.
Naphthalene: A possible human carcinogen linked to nasal tumors in animal studies, and a hemolytic agent at higher exposures. Used as a wood preservative in some treated wood products and older mothproofing for wood storage. Same mitigation as toluene: ventilation and off-gassing time.
In short: for solid wood pieces where the only Prop 65 trigger is wood dust or silica, the consumer exposure is essentially zero once the piece is in your home. For engineered wood and solvent-finished products, ventilation and off-gassing time meaningfully reduce exposure. For CCA-treated wood and any current product still using methylene chloride, choose a different product or seal what you already have.
Certifications for Healthier Wood
What does it mean for furniture to be GreenGuard certified, and is the whole product certified?
Not necessarily. GreenGuard certification can be awarded to a whole assembled product, an individual component (a finish, a foam, a fabric, a laminate), or even a single raw material. A brand can certify just the finish on a dresser and still advertise the dresser as "GreenGuard certified," without the engineered wood substrate or the adhesives bonding the layers having gone through any testing at all. This is different from OEKO-TEX Standard 100, which certifies the finished textile as a whole. So when you see GreenGuard or GreenGuard Gold on a wood product, the actual question is what exactly the certification covers. The strongest version is whole-product certification on the assembled piece, where the substrate, binders, finish, stain, and any paint are tested together as the final emitter. The weaker version is component-only certification, where one part of the product was tested in isolation. Both can carry the same logo. The way to tell is to ask the brand directly which version they hold, or look up the product in the UL SPOT database to see what's actually certified.
What is FSC certified wood?
FSC, or the Forest Stewardship Council certification, is focused on responsible management of forests. For wood, it means that the trees it comes from meet forest management standards, indigenous people’s rights are respected when harvesting, and old growth forests are not disturbed. It’s a fantastic certification in terms of our environment and community, but FSC-certified wood can still be treated or finished with many other chemicals that harm your health.
What is engineered vs plywood vs composite vs MDF vs particleboard?
What do you mean by “wood”?
I use “wood” with quotation marks to describe wood-like products that contain a mixture of wood, resins, and plastics. It covers engineered wood, plywood, MDF, particleboard, composite wood, OSB, and others.
What is engineered wood?
Engineered wood consists of thin pieces of solid wood attached with glue to either side of a non- solid wood core. The core can be either plywood or ground wood fibers mixed with resin— basically a glue. The outer solid wood surface is called a veneer. The glue holding the veneers onto the core, and the glue-based binders in the core, are where the health issues potentially lie, since these glues typically contain urea-formaldehyde, a carcinogen and airway irritant.
Happily, some of the newer engineered wood uses bio-based or formaldehyde-free glues that are much healthier than the old engineered woods.
Engineered wood is often used in furniture construction, like in making couches, because it can be stronger than some types of solid wood and can hold up to many years of wear and tear.
What is engineered hardwood? Is it different than regular engineered wood?
No, it’s the same thing. My guess is that this phrasing is a marketing term used to make the product seem a little more like it’s true hardwood.
What is "solid engineered hardwood" and is it the same as solid wood?
No. "Solid engineered hardwood" is a marketing phrase that means a thin layer of real hardwood bonded to a "wood" core, usually plywood or MDF. The word "solid" in this context refers to the surface layer being a continuous piece of real wood rather than a printed image or veneer pieced together, not to the entire product being solid wood. True solid wood means the same piece of wood goes all the way through the product, with no engineered core, no glued layers, and no thin veneer on top. If a product description uses "solid engineered hardwood," "engineered hardwood," or "real hardwood floor" without the word "solid" applied to the entire piece, the structure is engineered, not solid. The distinction matters because engineered cores bring binder chemistry that solid wood doesn't have.
Is engineered wood toxic?
It depends entirely on what the glue/resin/binder is that holds the wood together. If it is held together with a soy-based resin with no added formaldehyde, for example, then it’s a healthy option. If it is held together with a glue that contains formaldehyde, or a glue that contains other harmful chemicals like isocyanates, then it is harmful to health.
What is plywood?
Plywood is made of many layers of super-thin pieces of solid wood. Each layer’s grain is stacked perpendicular to the one above and below it, and all the layers are attached with an adhesive binder (plywood can have up to 3.5% binder by weight). Alternating the wood grain at perpendicular angles makes plywood even stronger than wood, and is why you see it used for home construction. After the layers are glued together, heat and pressure are applied to make a smooth plywood panel.
Like engineered wood, there are newer, healthier versions of plywood that are made with formaldehyde-free, soy-based resins instead of standard glues. PureBond is an example of a brand that is doing this.
What is composite wood?
Composite wood is very similar to engineered wood, but the materials in the core aren’t always wood-based. Instead, it is often a blend of plastics and wood.
What is MDF?
MDF means medium-density fiberboard and it is made with wood pulp mixed with a resin binder (with up to 10% by weight) to make a wood-like product. This is what IKEA uses in their cupboards, for example, then covers them with a layer of laminate.
What is particleboard?
Particleboard is a type of composite wood made with wood chips mixed with a binder (up to 12% by weight) to make a wood-like product. This is what IKEA uses in its KALLAX furniture, for example.
What are other types of engineered and composite wood?
Oriented Strand Board (OSB), Hardboard, Laminated Veneer Lumber, Glulam, and other wood-type products are some of the other types of engineered wood (and there are a lot!) These are a little different than plywood, MDF, and particleboard for two main reasons: one, they’re not regulated by the EPA to ensure that they contain low levels of formaldehyde, so may have higher levels of harmful off-gassing. Second, they’re less common in furniture, which of course, Interior Medicine focuses on, so that’s all I have to say about them!
What chemicals are in engineered wood?
It's hard to know, unless the brand discloses, which is rare. The Healthy Materials Lab maintains a list of brands that do. The main chemicals of concern in engineered wood come from the binders that hold the wood fibers, chips, or veneer layers together. Urea-formaldehyde is the dominant binder in standard plywood, MDF, and particleboard, and is the most common health concern in this product category. Phenol-formaldehyde is a related binder used more often in exterior-grade plywood and OSB; it emits less formaldehyde than urea-formaldehyde but is still a source. Isocyanates, specifically MDI (methylene diphenyl diisocyanate), are used in some newer no-added-formaldehyde products; MDI reacts away during curing but raises worker exposure concerns at the manufacturing stage. Beyond binders, any stain, paint, or finish applied to the engineered wood brings its own chemistry, which is why whole-product certifications like GreenGuard Gold are more informative than binder-only claims.
Is bamboo solid wood?
Sometimes! Bamboo is technically a grass, and can be solid, or more like engineered wood, when used in home products. Solid bamboo is rarely, but sometimes used as flooring. More often, like you see in butcher blocks or cutting boards, bamboo is processed in a vertical or horizontal fashion, a lot like plywood— thin strips of bamboo are glued and compressed together to make a strong, solid board. Or, bamboo veneers are glued to cores made with a variety of materials, depending on the brand.
Formaldehyde in Wood
Does all wood have formaldehyde in it?
Yes, trees emit around 2-9 parts per billion (depending on the species) of naturally occurring formaldehyde, so therefore, all wood contains some. This is why the term “no added formaldehyde” or NAF is preferred for wood and “wood” products— it’s more technically correct. The laws passed in 2010 that regulate added formaldehyde-based resins in “woods” like plywood, particleboard, and MDF, limit the formaldehyde emissions to between 50-110ppb depending on the wood product type. That’s around 10x above naturally occurring levels in wood, but still significantly lower than the levels allowed before 2010.
What is NAF engineered wood (and ULEF?)
NAF stands for “No Added Formaldehyde.” This means the binders used to glue the wood together don’t contain urea-formaldehyde.
ULEF means Ultra-Low Emitting Formaldehyde, and may be achieved by adding a chemical that sequesters, or captures, formaldehyde from escaping. These are called Formaldehyde Scavengers. It may also mean there is a blend of formaldehyde and non-formaldehyde based binders.
Composite wood that is “CARB or TSCA compliant” means that it has low formaldehyde levels, but not ultra-low. Since 2019, all plywood, MDF, and particleboard manufactured or imported into the US must be compliant.
Wood Veneers
What is a wood veneer?
A wood veneer is a very thin slice of real wood, usually less than 1/16 of an inch thick. It's glued onto a cheaper core material so the whole thing looks like it was made of solid wood. This is really common in cheap furniture. Veneers let brands use less expensive material underneath like MDF or particleboard (made of wood dust and glue mixed together) while still showing a real walnut, oak, or maple grain.
Are veneers plastic?
No. A true wood veneer is real wood. The confusion comes from look-alike surfaces that aren't wood at all, like melamine, thermofoil, and laminate. Those are plastic or resin layers printed with a wood-grain pattern. If a product says "wood veneer," it should be real wood. If it says "wood-look," "wood-grain finish," or "laminate," it's usually plastic.
What's under a wood veneer?
It depends on the brand, but the most common ones are:
MDF and particleboard: wood fibers or chips mixed with resin glue and pressed into sheets. Glue runs all the way through the board.
Plywood: many thin layers of wood veneer glued together, with the grain alternating direction for strength. There's a glue layer between every sheet. Now that the glue’s formaldehyde levels are regulated in the US, plywood is generally able to meet low VOC emissions standards and is becoming a healthier choice.
Blockboard: a core of solid wood strips sandwiched between veneer sheets. It uses less glue than MDF or even plywood, because most of the core is solid wood.
What makes one type of wood veneer safer than another?
Mostly the glue, both in the core and holding the veneer to it.
MDF and particleboard have the most glue, plywood has glue between every layer, and blockboard has the least. The type of glue matters, too. Urea-formaldehyde glues can off-gas formaldehyde for years. No-added-formaldehyde (NAF) options like soy-based or PVA glues are much better.
Since you can't see inside the core, I look for whole-product certification like GreenGuard GOLD. It tests the finished piece, so it covers the core, the glue, and the finish all at once. On my Wood scale, engineered wood with veneer can rate Healthy with that certification. Without it, it rates OK at best, and only when the brand discloses a no-added-formaldehyde glue.
Vinyl “Wood”
What is thermofoil and how do I spot it on furniture?
Thermofoil is a thin layer of vinyl heat-pressed and vacuum-sealed onto an MDF core, despite the misleading "foil" in the name. It contains no metal at all. It's used on cabinet doors, kitchen cabinetry, and a lot of low-cost flat-pack furniture, including several IKEA cabinet lines (GRIMSLÖV, RINGHULT, VOXTORP). The visual giveaway is a perfectly seamless, glossy or matte surface with slightly rounded door edges, no visible brush marks or seams, and a plastic-feeling smoothness. Thermofoil also tends to peel, bubble, or crack at the edges with age and heat exposure, which is the easiest way to identify it on older pieces. It often gets visually mistaken for painted wood because that's the look it's designed to mimic.
Is vinyl flooring toxic?
“Luxury” Vinyl Plank (LVP) is made from PVC, which requires vinyl chloride in production, a well-documented carcinogen that poses risks to workers and communities near factories.
The plasticizers used to soften PVC have historically included phthalates, which are endocrine disruptors, but most major manufacturers have phased these out in favor of phthalate-free alternatives like DOTP. DOTP’s long-term health profile is still being studied. Some LVP is coated with PFAS on the top layers for water and stain resistance.
Certified low-VOC, PFAS-free, phthalate-free LVP from a reputable manufacturer is meaningfully different from an uncertified version. The precautionary case for avoiding LVP where you have better options rests primarily on PVC's production footprint, the unknown long-term health profile of phthalate alternative plasticizers, and potential PFAS coatings.
Are vinyl floors safe?
Even though most LVP doesn’t off-gas VOCs as strongly as versions made a few years ago, and many are made without phthalates now, it doesn’t mean they’re safe, especially if they’re coated in PFAS. Using rugs and washing hands regularly helps.
What should I do if I already have vinyl flooring?
If it’s in the budget, and you’re replacing it, choosing solid wood or linoleum (which is made of flax!) represent healthy options. if you’re not replacing it, use certified non-toxic rugs to help protect kids or babies hand and mouth contact with the floor. Mop or wet-vacuum often to remove any microplastics, PFAS, or semi-volatile chemicals that shed off from it with wear and tear and become part of the dust.
Is laminate flooring safe?
Laminate flooring can be safer than LVP. It can have some wood in its core, or be 100% plastic, depending on the brand. The top layer is a piece of fiberboard with a photo of wood laminated to the top, then covered in a wear-resistant coating. This coating can be scratch-resistant, or water-resistant. Look for PFAS-free versions.
Wood Stains
Are wood stains toxic?
Water-based wood stains are relatively non-toxic, especially ones with certifications like GreenSeal-11 ensuring the most harmful additives are avoided. Ones with low VOCs, and no antimicrobials or heavy metals are a better choice.
Are water-based wood stains safer than oil-based stains?
Yes. For stains, water-based options are lower in VOCs than oil-based stains. Water-based stain is the healthier choice.
What is the difference between wood stain and wood finish?
Wood stains add color to natural wood, while a finish protects it.
Wood Finish Family Tree
How oils, waxes, shellac, lacquer, varnish, and polyurethane are related, sorted from healthiest to least healthy
Wood finishes
- Penetrating finishes Soak into the wood fibers instead of forming a layer on top.
Generally the healthiest option
- Pure drying oils (tung, linseed, hemp) Harden inside the wood by reacting with oxygen in the air. Examples: Hope's 100% Tung Oil, Real Milk Paint Co. Pure Tung Oil, Tried & True
- Hard wax oil A blend of drying oils and wax that adds a little more surface protection. Examples: Rubio Monocoat, Osmo Polyx-Oil, Fiddes Hard Wax Oil
- Wax (beeswax, carnauba, paste wax) A soft, thin buffed-on layer with light protection. Examples: Howard Feed-N-Wax, Minwax Paste Finishing Wax, Briwax
- Non-drying oils (mineral oil) Soak in but never harden, so they need to be reapplied regularly. Examples: Howard Cutting Board Oil, John Boos Mystery Oil, Thirteen Chefs Mineral Oil
- Oil-varnish blends Oil mixed with varnish and thinned with solvent, so not pure oil despite the name. Examples: Watco Danish Oil, Watco Teak Oil, Minwax Tung Oil Finish, Formby's Tung Oil Finish Use caution: contains solvent and varnish
- Film-forming finishes Dry into a hard layer that sits on top of the wood.
- Water-based Resin particles float in water and fuse into a film as the water evaporates.
Generally OK
- Water-based polyurethanepolyurethane Polyurethane resin carried in water instead of solvent. Examples: Varathane Ultimate Polyurethane (water-based), General Finishes High Performance, Bona
- Water-based lacquer or acrylicacrylic Acrylic, sometimes blended with polyurethane, carried in water. Examples: Minwax Polycrylic, Target Coatings EM6000
- UV-cured Hardens in seconds under ultraviolet light, with little to no solvent.
Generally OK
- UV acrylic lacqueracrylic The clear finish on a lot of flat-pack furniture. Factory-applied, like the "clear acrylic lacquer" on many IKEA products
- Evaporative Harden as the solvent evaporates, and can be redissolved by that solvent later.
Mixed: depends on the solvent
- Shellac A natural resin from the lac insect, dissolved in alcohol. Examples: Zinsser Bulls Eye Shellac, Zinsser SealCoat Among the healthiest
- Nitrocellulose lacquer The traditional furniture lacquer, carried in strong solvents. Examples: Deft Clear Wood Finish, Minwax Clear Brushing Lacquer Use caution
- Solvent acrylic lacqueracrylic A non-yellowing clear lacquer for white or pale wood. Mostly professional spray products, like Mohawk Use caution
- Reactive, solvent-based Harden through a chemical reaction, and can't be redissolved once cured.
Generally use caution
- Oil-based varnish Oil cooked with resin that cures in air, including alkyd and spar varnish. Examples: Epifanes Clear Varnish, Pratt & Lambert 38
- Oil-based polyurethanepolyurethane A varnish made with polyurethane resin instead of traditional resins. Examples: Minwax Fast-Drying Polyurethane, Minwax Wipe-On Poly, Varathane Oil-Based Polyurethane
- Catalyzed lacquer and conversion varnish Cured with an acid catalyst, and many use formaldehyde-based resins. Factory and cabinet-shop finishes, like Sherwin-Williams Sher-Wood and ML Campbell
- Two-part polyurethane ("PU lacquer")polyurethane Mixed with an isocyanate hardener right before spraying. Factory-applied, common on furniture made in China and Southeast Asia
- Water-based Resin particles float in water and fuse into a film as the water evaporates.
Generally OK
Wood Finishes
Why are plant oil finishes, but water-based stains, safer?
Finishes: Plant oil finishes like linseed oil, hemp oil, or tung oil are minimally processed and very low in VOCs. Water-based wood finishes are lower in VOCs than solvent-based ones, but they still contain synthetic polymers and some solvents to help them cure.
Stains: On the other hand, oil-based stains typically have higher VOCs, whereas their water-based counterparts have less.
Are water-based finishes safer than oil-based finishes?
No. The ranking from healthiest to least healthy for finishes is: plant oil and wax, water-based polyurethane or acrylic, then solvent-based finishes.
Plant-based oil finishes like tung oil, linseed oil, hemp oil, and hard wax oil are minimally processed and very low in VOCs, making them the healthiest finish option.
Water-based polyurethane and acrylic finishes are lower in VOCs than their solvent-based counterparts, but they still contain synthetic polymers and some VOC solvents, and they're not necessarily safer than a plant oil finish.
Solvent-based finishes (lacquer, varnish, oil-based polyurethane) are the highest in VOCs and the strong smell of a newly finished piece is the solvents evaporating as the finish cures over hours to weeks.
What are plant-based oil finishes?
Linseed, hemp, and tung oil are types of plant-based oil finishes. Linseed oil comes from the flax plant. Hemp oil comes from the cannabis plant. Tung oil comes from the Tung tree (Vernicia fordii), native to China, Myanmar, and northern Vietnam.
Is mineral oil safe?
Now it is relatively safe, as long as it is highly refined and purified. Mineral oil comes from petroleum, and in the past, it wasn’t refined as well, so it contained carcinogenic polycyclic aromatic hydrocarbons (PAHs) and other impurities. Now, the refining process is better, and highly refined and purified mineral oil is generally considered safe for use in cosmetics and food. It is not known to be carcinogenic to you in this version, and is applied to many cutting boards and wooden utensils and serving dishes because of its water resistance.
I personally exercise the precautionary principle with mineral oil. It’s not directly carcinogenic to you, but it depends on petroleum extraction, solvents, and refineries, which is not good for people or planet long term, and I don’t consider it as safe as a plant-based finish.
What are solvent-based finishes?
Varnish, acrylic, solvent-based lacquer, and urethane-based finishes all require a much higher solvent concentration than water-based finishes, so are quite high in VOCs that irritate your respiratory tract and can cause other issues.
What is a lacquer top coat?
A lacquer top coat is a clear or tinted finish sprayed onto wood. It dries into a thin, hard film on the surface, also called a film-forming finish: it sits on top of the wood instead of soaking in the way plant oils or hard wax oils do. Lacquer dries fast and resists scratches, water rings, and stains, which is why it's so common, especially on furniture from big brands.
There are three main types of wood lacquer:
Solvent-based lacquers (the most off-gassing). These use chemical solvents like toluene that evaporate as the finish dries. They release the most VOCs, and while most of it cures and emissions drop greatly after that, some can keep off-gassing in your home. These are used most often on imported furniture, factory-made kitchen cabinets, and antiques.
Water-based lacquers (low off-gassing): These use water instead of solvents. They start with far fewer VOCs, so there's much less to off-gas. They're growing in popularity because of tighter VOC regulations, and health-focused brands use them most.
UV-cured lacquers (very low off-gassing): These harden in seconds under ultraviolet light and use little to no solvent. They're common on flat-pack furniture. Emissions are very low when the finish is fully cured. The main open question is whether small amounts of uncured ingredients remain if the curing wasn't thorough.
A product that just says "lacquer" doesn't tell you much, but asking the brand whether their lacquer is water-based, solvent-based, or UV-cured will help.
Is wood lacquer toxic?
It depends on the type of lacquer, whether it has fully cured, and whether it has GreenGuard GOLD certification. From healthiest to least healthy:
Lacquered wood with whole-product GreenGuard GOLD certification rates Healthy, because the finished piece has been tested for emissions.
Solid wood with a water-based lacquer, with no whole-product certification, rates OK.
Solid wood with a solvent-based lacquer rates as Use Caution.
Is shellac toxic?
It depends if you’re talking about natural shellac or synthetic shellac. Natural shellac comes from the cocoon-like secretions of the female lac bug. Synthetic shellac contains solvents, and often releases high VOCs.
What is milk paint?
Milk paint is one of the oldest paint formulations, dating back thousands of years. It's made from milk protein (casein), lime (calcium hydroxide), natural pigments, and sometimes small amounts of borax or clay. When mixed with water, these ingredients create a durable, matte paint that bonds exceptionally well to porous surfaces. Milk paint typically comes as a powder that you mix yourself, which allows you to control the consistency and ensures no preservatives are needed for storage. As it dries, milk paint cures through a chemical reaction rather than simply evaporating water, creating an extremely durable finish that can last decades. Milk paint creates a characteristic flat, chalky appearance with subtle variations in color and opacity that many people like a lot for furniture and cabinetry. It's popular for getting a colonial or farmhouse look. Because it bonds through absorption rather than adhesion, milk paint works best on raw wood or porous surfaces and may not adhere well to previously painted or sealed surfaces without a bonding agent. It’s not a common choice for walls!
What is chalk paint?
Chalk paint (not to be confused with chalkboard paint) is a modern decorative paint that creates a matte, chalky finish similar to milk paint but with a completely different formulation. Most chalk paints are actually acrylic-based paints with calcium carbonate (chalk) added for texture and opacity, plus other additives for the signature matte finish. While marketed as low-VOC and easy to use without primer or sanding, most chalk paints are not truly non-toxic—they typically contain acrylic polymers and other synthetic ingredients. Chalk paint is beloved for furniture makeovers because it requires minimal prep work and creates a vintage, matte look. However, from a health perspective, chalk paint is not as safe as truly natural paints like milk paint, limewash, or clay paint. If you want the aesthetic of chalk paint but with healthier ingredients, milk paint is the better choice.
FYI: How and why I use the words non-toxic, chemical-free, toxin, and toxic
I use the words non-toxic, chemical, toxin and toxic, even though there is no agreed-upon definition of the term non-toxic, and that everything, even water, is made of chemicals, so nothing is truly chemical-free. Likewise, toxin refers to a natural substance like a plant poison or venom, whereas toxicant is a more accurate term for the chemicals in products that have a negative health impact. I recognize that something that is toxic does not automatically make it a health risk.
I choose to use these scientifically inaccurate words anyway purely for practical purposes, for now. This is because these words are currently the most culturally agreed-upon, descriptive, and accessible terms that allow people to find the information they’re looking for.
In short, “non-toxic” is shorthand for a complicated problem. I’ll update my terminology if this changes!
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FYI, “non-toxic” has no official definition, so I rate every product with the same method. It’s built on third-party certifications and published test data, not brand claims. For a deeper dive, my free course walks you through it.
Everything on Interior Medicine is educational information, not medical advice. Read my full disclaimer.
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