In the process of polymerization, some formaldehyde is released into the atmosphere. As the foam is setting up, smaller amounts of formaldehyde may be released to the air. However, there is a finite amount of formaldehyde that is available for off-gassing, so over time, the formaldehyde being emitted decreases steadily. Since it has been nearly 20 years since the insulation was installed, it is entirely probable that little or no available formaldehyde remains in the insulation. Urea-formaldehyde insulation is not the only source of formaldehyde in the home.
Many products use formaldehyde during the manufacturing process.
Formaldehyde consistently ranks among the top 50 manufacturing chemicals by volume. It is a common ingredient in many household furnishings and consumer products. Finally, formaldehyde is synthesized within the human body as a natural metabolite of methanol. Because this is so, the human body has built in mechanism to metabolize formaldehyde. This metabolic pathway must be overwhelmed before adverse affects are observed.