Hi mamakaw,
I would add a “ditto” to Daniels comments.
While some people may be unusually sensitive to some materials due to certain medical issues such as MCS (multipal chemical sensitivities) or may be sensitive to some materials that the large majority of people would be fine with and these types of exceptions are really impossible to predict … if the foam has a reliable certification for harmful substances and VOC’s (see post #2 here) then outside of these more unusual circumstances or outside of those people who may prefer more natural materials for “personal” or lifestyle reasons (rather than “safety” reasons) … they would certainly be “safe enough” for the very large majority of people to sleep on.
Any initial odor can last for anywhere from a day or two to a few weeks before they diminish to levels that most people wouldn’t notice depending on the type of mattress and the materials inside it and on the sensitivity of the person.
As Daniel also mentioned … there is a great deal of exaggerated material on the web about “toxins” and “chemicals” and after 3 years it would be very unlikely that any offgassing would be at a level that would be harmful and probably weren’t even when the mattress was new.
Phoenix