What is formaldehyde?
In one line: formaldehyde is a common indoor VOC — a gas released by pressed-wood furniture, flooring, adhesives and some fabrics. Because it's a gas, a particle filter (HEPA/MERV-13) won't remove it; ventilation and activated carbon are what help.
What it is and where it comes from
Formaldehyde is a colourless gas with a faint sharp smell, and one of the most common indoor VOCs. Typical sources include MDF and chipboard furniture, laminate flooring, plywood, glues and resins, some insulation and textiles, and smoke. It's released (off-gassed) most strongly when items are new and tails off over months — so new furniture or a newly fitted room is a common cause of a "chemical" smell. It's classified as a human carcinogen, so keeping indoor levels low is worthwhile.
Why HEPA can't remove it
Formaldehyde is an individual gas molecule, far smaller than any particle a HEPA or MERV-13 filter can catch — it passes straight through. This is the same reason particle filters don't remove smells: for gases you need adsorption.
How to reduce it
- Ventilate — the fastest way to lower formaldehyde, especially with new furniture or after decorating.
- Activated carbon — a genuine carbon stage adsorbs formaldehyde and other VOCs; more carbon lasts longer (some carbon is treated specifically for formaldehyde).
- Choose low-emission products — look for low-formaldehyde or E1/E0-rated boards and low-VOC paints.
- Give new items time to off-gas, ideally ventilated, before heavy use in bedrooms.
Next step
Tackling VOCs and off-gassing? See the VOCs & new-build guide and carbon-equipped units at Best Air Purifier UK.
FAQ
Does a HEPA air purifier remove formaldehyde? No — HEPA removes particles, not gases. You need activated carbon (and ventilation) for formaldehyde.
How long does new-furniture formaldehyde last? Emissions are highest when new and decline over weeks to months; ventilation and carbon manage it in the meantime.