I'm looking to purchase a sofa, but have been bombarded with all kinds of internet info about the toxicity of certain materials used to make sofas. For example, polyurathane foam is labeled as toxic--is this true? Is something like a blend of cotton/polyester and polyurethane toxic?
The polyurethane would have to be absorbed through your pores when you're in contact with the sofa. That's not going to happen easily? Theres a few tangent articles about the safety of these so called "cheap" sofas and mattress on livestrong and other websites. I'd say it's not a concern. Sofa on bro.
Polyurethane is a polymer that's made up of toxic chemicals that react pretty completely with each other during the manufacturing process. While there's always potential that there could be residual unreacted materials, I'd say the risk of exposure to these is very minimal.
More important would be to look out for formaldehyde. It's a component in some of the adhesives that are commonly used in furniture making. New furniture can off-gas formaldehyde. If located in a room that doesn't get a lot of fresh air (either through the HVAC system or through building envelope leakage), then concentrations can build up. Sensitive individuals will experience upper respiratory tract and eye irritation. Long term exposure can cause sensitization - even small exposures would then lead to asthma like symptoms. It's also a recognized carcinogen, for good measure.
Problems mostly occur in office settings where they replace all the furnishings at once, and get a lot of off-gassing for the first several months. In a home environment, if you're just buying a sofa, it could still cause issues, but it's less likely.
The other broad category of chemicals to beware of are flame retardants. It's impossible to cover the full scope of these here, but suffice to say that different compounds are linked with health effects including atopic dermatitis, allergic rhinitis and asthma, and possibly endocrine disruption. Interesting to note that most Americans have measureable concentrations of various flame retardant chemicals in their blood. Related to this, there's a group of scientists that have come out strongly against incorporating flame retardants into furniture: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3002202/