Hi lakosil,
It depends on the type of foam you are referring to, the testing certifications they have for harmful substances and VOC’s, and where the foam is manufactured.
For almost all adults … I would look for memory foam and polyfoam that was manufactured in North America or that was CertiPur certified if it wasn’t. Almost all latex has been certified by OekoTex standard 100 or other similar testing protocols which is even more stringent than CertiPur and would be fine as well.
ADMIN NOTE: *Removed 404 link|Archived Footprint: certipur.us/pages/for-industry/find-a-foam-supplier/
For younger children I would tend to look for foams that are certified by OekoTex standard 100 class 1 (safe for children). I would also consider polyfoam that was CertiPur certified in the base layer of a mattress but I would tend to avoid memory foam because of possible support / alignment issues for children (who need firmer mattresses) and for possible sensitivities to memory foam. Post #2 here also has links to some of the better threads on the forum about mattresses and children.
Some people may also be more sensitive than the large majority of people who would be fine with these guidelines and certifications or have unusual health issues such as MCS (multiple chemical sensitivities) or be more concerned about some of the fire barriers or glues or other components used in mattresses or may be more comfortable with more natural materials for personal reasons and in this case they may have a different answer to the question of “how safe is safe enough for me” than most people. In this case it can take a great deal of additional research into different materials and components used in mattresses that can lead to a lot of complex and conflicting information and for those who are in this smaller group and are willing to take the time and do the research then post #2 here and the many links and sources of information it includes would be a good place to start.
Phoenix