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. Plants do work in sealed test containers surrounded by grow lights, but real-world tests show that plants have no detectable effect on particulate pollution (1) indoors (including tests I did in Beijing). So it’s important to have real-world data.
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. The data showed formaldehyde fell 48% one year after remodeling.
After two years, formaldehyde dropped to the same levels as in older homes.
Bottom line: The data suggests it takes about two years for formaldehyde to off-gas down to levels of the average home.
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.
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.