USEPA Update

Summary:
Based on sufficient evidence in animal testing, human data includes nine (9) studies that show statistically significant associations between exposure to formaldehyde containing products and site-specific respiratory neoplasm's. When inhaled, formaldehyde was causing cancer in the nose and trachea of hamsters, and nasal cancers in rats. Analysis of the remaining 19 studies indicate that leukemia and neoplasms of the brain and colon may be associated with formaldehyde exposure.
See California EPA report regarding the off-gassing of Formaldehyde from Particle Board furniture and closets.

From the US EPA: What should I know about Formaldehyde and Indoor Air Quality? Highlights:

In homes, the most significant sources of formaldehyde are likely to be pressed wood products made using adhesives that contain urea-formaldehyde (UF) resins.... Medium density fiberboard contains a higher resin-to-wood ratio than any other UF pressed wood product and is generally recognized as being the highest formaldehyde-emitting pressed wood product....

...In homes with significant amounts of new pressed wood products, levels can be three times the amount of older homes.

Direct link: https://www.epa.gov/indoor-air-quality-iaq/what-should-i-know-about-formaldehyde-and-indoor-air-quality