How much formaldehyde is too much indoors?

The World Health Organization guideline for indoor air is 0.1 mg/m³ of formaldehyde averaged over 30 minutes. In the measurements Coridum holds, a room with newly installed laminate flooring reached a mean of 0.038 ppm (F-0013), and a modelled residential room with 20 m² of medium density fibreboard at a ventilation rate of 0.5 h⁻¹ reached 0.093 mg/m³ (F-0015). The numbers that get quoted most often — class E1, E0.5, ENF — are none of these: they are limits for what a panel may emit in a test chamber.

Where it comes from indoors

Almost all of it comes from things made with resin. Wood-based panels — particleboard, medium density fibreboard, plywood — are bonded with formaldehyde-based adhesives, and the panel continues to release a small part of that for as long as it is in the room. Laminate flooring is a panel with a decorative surface, and behaves the same way. Furniture, kitchen carcasses, shelving and door blanks are all the same material under different names.

The consequence is that formaldehyde indoors is usually a question about surface area, not about a single object. One shelf changes nothing measurable; forty square metres of new fitted units in a closed flat is a different situation, and the same panel emitting the same amount per square metre produces a different concentration in each.

Exposure limits by jurisdiction

Two kinds of number are routinely confused here, and separating them is most of the answer to the question in the title.

What it applies to	Body	Value	Averaging or test	Source
The air in a room	World Health Organization	0.1 mg/m³	30 minutes	WHO indoor air quality guidelines, 2010
A panel or article	European Union, class E0.5	0.062 mg/m³	chamber, EN 717-1	F-0016
A panel	European Union, class E1	0.124 mg/m³	chamber, EN 717-1	F-0018
A panel	China, grade ENF	0.025 mg/m³	GB/T 39600-2021	F-0019
A panel	United States, hardwood plywood	0.05 ppm	large chamber, ASTM E 1333	F-0017

Only the first row is a value for the air you breathe. The rest are product limits, and a product that meets them can still produce a concentration above or below the guideline depending on how much of it there is and how the room is ventilated. The full set of ten product thresholds, with the test method for each, is in the formaldehyde emission limits table. Slovakia, the United Arab Emirates and Hong Kong are being compiled.

What it is linked to

The evidence Coridum holds on health effects is narrow and worth stating precisely rather than broadly. In a study of people with atopic dermatitis, those whose indoor formaldehyde fell by more than the group mean (a fall of 41.9 µg/m³) showed a greater reduction in their severity score than the rest: −2.69 against −1.48 (F-0026). The study did not state whether that difference was statistically significant, and it is a comparison within one group of people rather than a controlled trial.

That is the whole of what this article can say about health. The general case for keeping formaldehyde low rests on the World Health Organization guideline and the reasoning behind it, not on measurements held here.

What reduces it

Choosing the material. A panel certified to a stricter class emits less by definition, and that is source control at the point where it is cheapest — low-emission materials cost nothing extra to specify before an order is placed and cannot be retrofitted afterwards.

Ventilation is the second lever, and the modelled value above shows why it matters as much as the material: the 0.093 mg/m³ figure is not a property of the board, it is what 20 m² of that board produces at an air exchange rate of 0.5 h⁻¹ (F-0015). Double the exchange rate and the same board gives a lower number.

How strong is the evidence

Grade C for the source–factor link: newly installed laminate flooring and wood-based panels may be associated with raised indoor formaldehyde (C-0007), supported by consistent measurements in more than one study, with no contrary finding recorded.

Weaker than that for anything about health. The single relevant finding (F-0026) reports a difference in symptom score without stating significance, in people who already have a skin condition. It cannot carry a general statement about formaldehyde and health, and none is made here.

The product limits are a third kind of evidence again: they are what regulators decided, documented in one review (CKB 1163) and one study (CKB 0257), not measurements of any room.

What would settle it

A measurement in the room in question, over a period long enough to include the times when it is closed. The guideline is a 30-minute average, so a single reading taken with the window open answers nothing. What would settle the health question is a different kind of study altogether — one that changes the concentration deliberately and follows what happens — and the evidence layer behind this article does not contain one.