Safe formaldehyde levels & how testing works

The WHO indoor air guideline for formaldehyde is 0.1 mg/m³, measured as a 30-minute average — the same benchmark used by Singapore's SS 554 standard for air-conditioned buildings. Readings below about 0.06 mg/m³ are comfortably safe, readings between 0.06 and 0.1 are within the guideline, and readings meaningfully above 0.1 warrant action. Formaldehyde is classified as a Group 1 carcinogen by the IARC, which is why the guideline exists — but the number on a calibrated meter, not the smell, is what tells you where your home stands.

What the numbers mean

Most professional meters display milligrams per cubic metre (mg/m³); some also show parts per million (ppm). The conversion is roughly 1 ppm ≈ 1.23 mg/m³ at 25°C, so the WHO guideline of 0.1 mg/m³ is about 0.08 ppm. In practical bands:

A just-renovated bedroom with new built-in wardrobes commonly reads in the elevated band — something like 0.24mg/m³ — while the post-treatment target for every room is 0.06mg/m³ or lower.

Why smell is an unreliable gauge

Two things make your nose a poor instrument here. First, olfactory fatigue: spend time in a home with elevated formaldehyde and you stop noticing the smell within hours, while the level itself hasn't changed. This is why owners often report that the smell "went away" after a week of living in — and why visitors notice it immediately.

Second, the detection threshold varies widely from person to person, and for many people it sits near or above the guideline itself. You can have a home reading above 0.1 mg/m³ that smells like nothing to you, and a safe home that still carries a faint new-furniture odour from other, harmless compounds. The smell and the number are loosely related at best — which is the whole case for measuring. (For what that renovation smell actually is, see what off-gasses and for how long.)

How professional testing works

A meaningful test reflects the conditions you actually live in. We ask you to keep windows and doors closed for 8–12 hours beforehand — overnight is ideal — so readings show what the home equilibrates to with the aircon running, not what it reads after a morning of airing out. On the visit, each room is measured at breathing height, plus inside wardrobes and cabinets, where emissions concentrate. Professional services use calibrated electrochemical meters, which respond specifically to formaldehyde and are checked against reference standards.

The consumer handhelds sold online for S$20–80 use semiconductor sensors that cross-react with alcohol, cooking fumes, perfume and humidity — they can read several times too high or too low depending on what else is in the air. They're fine for watching a trend in one room over weeks; they are not something to base a move-in decision on.

What to do at each band

• Safe (below 0.06): nothing. Genuinely. Keep the report for your records — useful if you later add furniture or renovate.
• Acceptable (0.06–0.10): no action required. If the renovation is recent or a baby is on the way, re-test after a few weeks, since levels move with heat and humidity.
• Elevated (0.10–0.30): either ventilate aggressively for several weeks and re-test, or book source treatment for a verified result — the sensible default if you're moving in soon.
• Significantly elevated (above 0.30): hold off on moving in, treat, and re-verify before occupancy — particularly with infants, pregnancy or respiratory conditions in the household.

If you don't yet have numbers, a S$180 testing visit gives you the room-by-room readings this guide is written around — including, about a fifth of the time, the news that you don't need anything else.