An important question about formaldehyde is how long it takes for formaldehyde to off-gas in new homes and new furniture–how long will it take for levels to get back to normal? The best data I’ve seen suggests formaldehyde takes about two years to off-gas back to normal levels.
Why We Need Real-World Tests
When researching this question, I really wanted to see tests in real-world apartments. I want to understand how formaldehyde acts in real homes, not in a laboratory plexiglass container. That’s critical because sometimes people take results from sealed boxes and incorrectly apply them to our homes.
For example, many articles trumpet how great plants are as purifiers, but real-world tests show that plants have no detectable effect on particulate pollution indoors (including tests I did in Beijing).
Real-World Formaldehyde Off-Gassing Tests
Fortunately, scientists in Hong Kong did real-world tests. They tested for formaldehyde and other VOCs in homes and then compared new/remodeled homes with older apartments.
They found that one year after remodeling, formaldehyde levels were down 48%.
After two years, formaldehyde levels were the same as in older homes. So the data suggests it takes about two years.
But it’s worth noting that these are home in Hong Kong. Why’s that important? Because temperature and humidity make formaldehyde off gas faster. In Beijing or New York, this off-gassing will probably take longer than in Hong Kong.
3 Things You Need to Know About Formaldehyde
Thomas is an Associate Professor of Behavior Science at the University of Chicago Booth School of Business and the founder of, a social enterprise to help people in China breathe clean air without shelling out thousands of dollars for expensive purifiers.