Formaldehyde is used in so many products that it is next to impossible to avoid it entirely. It is used in carpets, adhesives, plastics, draperies, plywood, particle board, some paints and other finishes, as well as some personal care products, and foods.
If you think back you may remember the big problem FEMA had with the temporary trailers that were supplied for hurricane Katrina victims.
At that time they recommended increased ventilation until the levels were reduced.
In any case, you may not always smell formaldehyde but they do make detectors that can tell you the level of formaldehyde in the air as well as test strips to tell you the amount of formaldehyde in your food. Formaldehyde is used in many food products to extend the shelf life.