What Is Formaldehyde?

Formaldehyde’s a colorless gas that’s common both outdoors and indoors. At higher concentrations it has a sharp, pungent smell. It’s produced naturally in small amounts by living things and by combustion, and it’s also manufactured in large quantities for use in building materials, household products, and industrial processes.

Quick Reference

• Simple definition: A colorless gas and common indoor air pollutant that can irritate the eyes, nose, and throat and is classified as a human carcinogen

• Main concern: Short-term irritation and, with higher or prolonged exposure, increased cancer risk

• Top places found: Pressed-wood products (particleboard, plywood, MDF), some insulation, fabrics, glues, and combustion sources

• Key action: Choose lower-emitting products, increase ventilation, and let new materials off-gas when possible

Why it Matters

Formaldehyde’s one of the most common indoor air pollutants. Even at relatively low levels it can irritate the eyes, nose, throat, and lungs. People with asthma or other respiratory conditions are often more sensitive. At higher concentrations or with long-term exposure, it’s classified as a known human carcinogen, linked especially to nasopharyngeal cancer and certain leukemias in occupational settings.

Indoors, levels are frequently higher than outdoors because so many building materials and furnishings release it. New products tend to emit the most; emissions usually drop over months as the material ages. Heat and humidity increase the rate of release, which is why problems can feel worse in warm weather or tightly sealed homes.

Where You Can Find It

• Pressed-wood products made with urea-formaldehyde resins — particleboard, hardwood plywood, medium-density fiberboard (MDF) used in furniture, cabinets, shelving, and flooring

• Some foam insulation materials

• Permanent-press fabrics, drapes, and some clothing

• Glues, adhesives, and finishes

• Combustion sources — tobacco smoke, unvented gas or kerosene heaters, wood stoves, and vehicle exhaust that enters the home

• Certain personal care products and cosmetics

• Outdoor air (from vehicle exhaust, industrial emissions, and natural sources), usually at lower concentrations than indoors

Pressed-Wood Products and Off-Gassing

The biggest indoor source in most homes is pressed-wood products held together with urea-formaldehyde resin. These materials are widely used because they’re inexpensive and versatile. When they’re new, they can release noticeable amounts of formaldehyde gas into the air.

The emission rate is highest in the first weeks and months after manufacture and gradually declines. Higher temperatures and higher humidity speed up the release. That’s why a new dresser, bookshelf, or laminate floor can make a room smell sharp or cause eye and throat irritation, especially in a warm or poorly ventilated space.

Not all pressed wood is equal. Products made with phenol-formaldehyde resins generally emit much less formaldehyde than those made with urea-formaldehyde resins. Some manufacturers now offer ultra-low-emitting or no-added-formaldehyde options. Looking for those labels (or for third-party certifications) when buying new furniture or cabinets can make a meaningful difference.

The Simple Explanation

Formaldehyde (chemical formula CH₂O) is the simplest aldehyde. It’s highly reactive and highly soluble in water, which is part of why it irritates moist tissues in the eyes, nose, and respiratory tract so readily.

It enters indoor air mainly through off-gassing from materials that contain formaldehyde-based resins and through combustion. Once in the air, it can stay until it’s ventilated out or reacts with other chemicals. Because it’s a gas at room temperature, it mixes throughout a space rather than settling like dust.

The body absorbs formaldehyde mainly through inhalation. At low levels the primary effects are irritation. At higher or repeated exposures, it can damage DNA, which is the basis for its classification as a carcinogen. Most of the strongest cancer evidence comes from industrial settings with much higher concentrations than typical homes, but indoor levels still contribute to overall exposure, especially in new or newly renovated spaces.

Formaldehyde is also a VOC — it evaporates readily at room temperature — so the same strategies that reduce other VOCs (ventilation, source control, choosing lower-emitting products) help with formaldehyde too.

Common Misconceptions

• “If I can’t smell it, it’s gone.” The sharp odor is noticeable at higher levels, but irritation can still occur at concentrations below the odor threshold for some people.

• “Only cheap furniture has this problem.” Any product made with urea-formaldehyde resin can emit, regardless of price.

• “Once the smell fades, emissions stop completely.” Emissions drop significantly over time but can continue at lower levels for months or longer, especially with heat and humidity.

• “Outdoor formaldehyde isn’t a concern.” Outdoor levels are usually lower, but they still add to total exposure, especially near heavy traffic or industrial areas.

What You Can Do About It

Practical steps focus on reducing sources and increasing fresh air:

• When buying new furniture, cabinets, or flooring, look for ultra-low-emitting, no-added-formaldehyde, or certified low-formaldehyde products.

• Let new pressed-wood items off-gas in a well-ventilated space (or outdoors if practical) before bringing them into regular living areas.

• Increase ventilation — open windows when weather allows, use exhaust fans, and consider a balanced ventilation system in tighter homes.

• Keep indoor humidity in a moderate range; high humidity increases emissions from existing materials.

• Avoid unvented combustion sources indoors and don’t allow smoking inside.

• Wash permanent-press fabrics before first use when possible.

No single step removes all formaldehyde, but reducing the strongest sources and improving air exchange lowers indoor levels for most homes.

Conclusion

Formaldehyde’s a common indoor gas that comes mainly from pressed-wood products, some furnishings, and combustion. It can irritate the eyes, nose, and throat at everyday levels and is classified as a human carcinogen with higher or prolonged exposure. Emissions are strongest when products are new and increase with heat and humidity. Choosing lower-emitting materials, letting new items off-gas, and improving ventilation are the most effective ways to keep indoor levels down.