Are There Glues Used in Infrared Saunas? The Hidden Danger Most Companies Won't Talk About

Here's something most infrared sauna companies would rather you didn't think about: you're sitting inside a heated wooden box, breathing deeply, for 30–45 minutes at 130–145°F. Whatever is in those materials — whatever adhesives, stains, finishes, or synthetic compounds were used to build that box — you are inhaling them.

This isn't theoretical. It's chemistry. When you heat wood products containing formaldehyde-based adhesives, the formaldehyde vaporizes and enters the air you're breathing. The hotter the environment, the faster the off-gassing. In a sealed sauna cabin at 140°F, you're creating ideal conditions for maximum volatile organic compound (VOC) release — and you're breathing it all in through deep, deliberate inhalation.

After twelve years of building custom infrared saunas and evaluating hundreds of competitor products, I can tell you with certainty: most mass-produced infrared saunas contain materials you would never knowingly choose to breathe. This article explains what's in them, why it matters, how to spot the problem, and how we build differently.

The hidden problem: what you can't see is what you're breathing

An infrared sauna looks simple — wooden walls, a glass door, heater panels, a bench. But what's behind those walls? What's under that bench? What adhesive holds those heater panels in place? What finish is on the wood? These questions matter enormously when the materials are being heated to temperatures that accelerate chemical off-gassing.

Most consumers never think to ask. The sauna arrives in a box, you assemble it, you turn it on, and you sit inside it. If there's a slight chemical smell during the first few uses, you assume it's "new furniture smell" and figure it'll go away. Sometimes it does — because the most volatile compounds gas off quickly. But formaldehyde emissions from engineered wood products continue for years. They decrease over time but never fully stop, and they spike every time you heat the enclosure. I've had clients contact us after purchasing a competing product specifically because the chemical smell never went away — even after six months of use and multiple "bake out" attempts. One client measured the air inside their two-year-old prefab sauna with a consumer VOC meter and found formaldehyde levels above 0.3 ppm at operating temperature — three times the EPA recommended maximum.

What cheap infrared saunas are actually made of

I've disassembled and inspected dozens of mass-produced infrared saunas over the years. Here's what I consistently find:

• Plywood wall and ceiling panels — layered wood bonded with urea-formaldehyde (UF) or phenol-formaldehyde (PF) adhesives. UF is the most common and the most problematic — it emits formaldehyde continuously, with rates accelerating dramatically at elevated temperatures.
• MDF or particle board in hidden areas — behind heater panels, under benches, inside door frames. These engineered wood products use even more adhesive per volume than plywood. They're cheap, they're flat, and they're loaded with formaldehyde.
• Synthetic caulks and sealants — around glass door panels, at wall joints, and where panels meet the floor. Many contain silicone compounds, acetic acid, or isocyanates that off-gas at elevated temperatures.
• Stains, varnishes, or polyurethane — applied to make cheap wood look better. These coatings contain VOCs including toluene, xylene, and formaldehyde. When heated, they release these compounds directly into the cabin air.
• Chemical-treated imported wood — treated with insecticides, fungicides, or preservatives for shipping and customs compliance. These treatments are rarely disclosed to consumers.
• Hot-melt adhesive on heater mounting — gluing heater elements directly to wall panels. When the heater reaches operating temperature (200°F+), the adhesive softens and off-gasses.

The formaldehyde risk: what the science says

Formaldehyde is not an obscure chemical concern. The World Health Organization's International Agency for Research on Cancer (IARC) classifies formaldehyde as a Group 1 carcinogen — the highest classification, meaning there is sufficient evidence that it causes cancer in humans. It's in the same category as asbestos, benzene, and tobacco smoke.

The key issue for sauna users is the relationship between temperature and emission rate. Research published in the Journal of Hazardous Materials and Building and Environment has documented that formaldehyde emissions from plywood and MDF increase 2–3 times for every 10°F (5.5°C) rise in temperature. This relationship is exponential, not linear.

Let's apply the math to an infrared sauna scenario. If a plywood panel emits X micrograms of formaldehyde per hour at room temperature (70°F), it emits approximately 8–27X at 130°F, and 16–81X at 145°F. In a small, sealed cabin — typically 30–50 cubic feet of air volume — these concentrations accumulate rapidly. You're sitting in that air, breathing deeply, for 30–45 minutes.

The EPA's recommended maximum formaldehyde exposure for indoor air is 0.1 parts per million (ppm). Studies on new manufactured homes with plywood and MDF at room temperature regularly exceed this threshold. Inside a heated sauna with the same materials, the concentrations can be dramatically higher. No comprehensive study has measured formaldehyde levels inside mass-produced infrared saunas at operating temperature — but the physics and chemistry make the concern impossible to dismiss.

How to spot a glued sauna: the buyer's checklist

Whether you're evaluating a new purchase or checking a sauna you already own, here's how to identify adhesive-containing materials:

1. Check behind the heater panels. Most heater panels are removable or have accessible edges. If the backing material is layered (visible layers of thin wood glued together), it's plywood. If it's smooth, dense, and uniform without visible wood grain, it's MDF or particle board.
2. Look under the benches. This is where manufacturers most commonly hide cheap materials. Lift the bench slats if possible. Is the support structure solid wood or engineered board?
3. Inspect door frame construction. Run your finger along the inside edges of the glass door frame. Is it solid wood or layered/pressed material? Is there caulk or sealant where the glass meets the frame?
4. The smell test. Heat the sauna to operating temperature and step inside. Close your eyes and breathe. A properly built sauna with solid wood and no adhesives should smell like natural wood — cedar, hemlock, or whatever species is used. If you detect a chemical, plastic, acrid, or "new furniture" smell, adhesives or finishes are off-gassing.
5. Ask for material safety data sheets (MSDS). Any legitimate manufacturer can provide MSDS documentation for every material in their product. If a company can't — or won't — provide this documentation, that's your answer.
6. Check the wood surface. Is it coated with a glossy or satin finish? Run a fingernail across it. Natural untreated wood has a matte, slightly rough texture. Varnished or stained wood feels smooth and sealed.

How SaunaCloud builds without a single drop of glue

When I founded SaunaCloud in 2014, the decision to build with zero adhesives wasn't a marketing angle — it was a fundamental engineering requirement. If you're building a device designed to heat the air inside it to 140°F while people sit in it breathing deeply, every material in that device must be safe to inhale when heated. This isn't negotiable.

Here's exactly what goes into a SaunaCloud sauna — and what doesn't:

100% solid Western Red Cedar

Every wall panel, ceiling board, bench slat, backrest, trim piece, and structural element is cut from solid A-grade Western Red Cedar. Not plywood with a cedar veneer. Not cedar-faced MDF. Solid cedar, full thickness, with grain running through the entire cross-section. You can see it. You can feel it. You can verify it yourself.

We choose Western Red Cedar specifically because it's naturally antimicrobial, antifungal, and rot-resistant — it doesn't require chemical treatments to perform in a hot, humid environment. The natural oils in the cedar (thujaplicins) provide built-in protection against bacteria, mold, and decay. Studies have shown that thujaplicin compounds inhibit the growth of Staphylococcus aureus, E. coli, and multiple species of mold and fungus — all without any applied chemicals. No stains needed. No varnishes needed. No polyurethane needed. The wood protects itself. This is why cedar has been the material of choice for saunas, closets, chests, and outdoor structures for centuries — long before synthetic preservatives existed. For a deeper look at why we chose cedar over every alternative, read our guide to premium materials in infrared saunas.

Tongue-and-groove joinery

Our wall and ceiling panels connect via tongue-and-groove profiles — each board interlocks mechanically with the next. No adhesive is needed. This is the same joinery technique used in traditional Finnish saunas for centuries — and for good reason. It's simple, it's strong, and it allows the wood to expand and contract naturally with temperature and humidity changes. This is actually a critical engineering point: cedar in a sauna undergoes thermal cycling from room temperature to 145°F and back, hundreds of times per year. Rigid adhesive joints resist this movement, creating stress fractures, delamination, and warping over time. Tongue-and-groove joinery accommodates the expansion and contraction naturally — each panel slides fractionally against the next without breaking the seal. The result is a structure that gets tighter and more stable over years of use, not weaker.

Stainless steel mechanical fasteners

Every structural connection uses stainless steel screws and brackets. Stainless steel doesn't corrode in high-heat, high-humidity environments, and it's completely inert — no off-gassing at any temperature. Every joint in a SaunaCloud sauna is mechanically fastened, not chemically bonded.

No finishes of any kind

The cedar in our saunas is delivered and installed with zero surface treatments — no stain, no varnish, no sealant, no polyurethane, no oil. When you step into a SaunaCloud sauna and breathe in, the only thing you smell is Western Red Cedar. That's it. That's by design. To see our full construction process, visit how we build.

What about the heaters?

This is a detail most people don't think to ask about, but it matters. Some manufacturers use hot-melt adhesive to bond heater elements to mounting panels. When the heater reaches operating temperature (200°F+), that adhesive softens and off-gasses — right next to the hottest surface in the enclosure.

VantaWave® heaters use exclusively mechanical mounting — stainless steel hardware rated for continuous operation at elevated temperatures. No adhesive touches any heat-producing component. The wiring uses high-temperature rated insulation, and the control panel components are industrial-grade — not consumer-grade plastics that degrade under thermal cycling.

The simple test: what does your sauna smell like?

Here's the easiest way to evaluate any infrared sauna's material quality: heat it to operating temperature, step inside, close the door, close your eyes, and breathe deeply through your nose.

If you smell cedar, pine, hemlock, or basswood — natural, pleasant wood aromas — your sauna is likely built with solid wood and minimal adhesives.

If you smell something chemical, acrid, plasticky, or reminiscent of new furniture — stop using it until you've identified the source. That smell is volatile organic compounds entering your lungs. It's not something that "goes away" — it's something that becomes less noticeable as your nose adapts, while the chemicals continue off-gassing at the same rate.

A SaunaCloud sauna smells like a cedar forest. On day one. On day one thousand. Because the only material in the enclosure is Western Red Cedar and stainless steel.

How to verify any manufacturer's claims

Claims about material safety are easy to make and hard to verify — unless you know what to ask for. Here's what a manufacturer should be able to provide if they're genuinely building with safe materials:

• Material Safety Data Sheets (MSDS) for every material in the sauna — wood, adhesives (if any), finishes, heater components, insulation, sealants. If they can't provide these, they either don't know what's in their product or they don't want you to know.
• Wood species certification — proof that the wood is what they claim it is. 'Canadian cedar' is a legitimate species designation; 'cedar-style wood' is not.
• EMF testing results from a third-party lab, not internal measurements. This doesn't directly relate to off-gassing, but it signals whether the company subjects their product to independent verification.
• A clear, specific answer to: 'Is there any plywood, MDF, particle board, or engineered wood product anywhere in this sauna?' Not 'our wood is all natural' — that's evasion. A yes or no answer to a specific question.
• Willingness to let you inspect a unit before purchase. If a company won't let you look behind the heater panels or under the benches in a showroom unit, ask yourself why.

At SaunaCloud, we invite inspection. We photograph our builds at every stage and share them with clients. You can see the solid cedar before the walls go up. You can see the tongue-and-groove joints before the ceiling is installed. You can see the mechanical heater mounts before the panels are placed. Transparency isn't a burden when you have nothing to hide. If you're evaluating saunas and want to understand what separates mass-produced from custom-built, read our complete buying guide or explore why 99% of infrared saunas are the same.

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