Most simply stated, polyurethane foam and flame retardants off-gas and decompose over time. The typical mattress and box spring is soaked in a strange brew of fire retardant chemicals, formaldehyde, and other toxic glues, stains, and coatings. These chemicals can release deadly and often carcinogenic gasses. Almost every mattress produced has some form of polyurethane foam, which tends to off-gas isocyanate (an agitator or catalyst which creates the foam bubbles). No studies have demonstrated that the trace amounts of isocyanate found in polyurethane foam off-gassing present any demonstrable health risk. Some people have reported headaches and irritation from certain brands of mattresses; its possible these reactions could be due flame to retardants (phosphorus, arsenic, antimony, and boron). If you find you are allergic to isocynate even in trace amounts, you may be disappointed to find the material is used in almost every mattress produced.