Is polyurethane toxic once dry?

Once fully dry and cured, polyurethane is generally not toxic and is considered safe for everyday use in homes. The toxicity of polyurethane comes from its liquid components, isocyanates and solvents, which evaporate during curing. When polyurethane is fully cured, which takes about 7 days for water-based and about 30 days for oil-based, it becomes an inert solid plastic that does not off-gas significant chemicals and does not leach toxins under normal conditions. This is why it is used on hardwood floors, dining tables, chairs, and even children's toys and is approved for indirect food contact after full cure by the FDA. However, there is an important distinction between dry to touch and fully cured. Dry to touch in a few hours does not mean fully cured and non-toxic, it can still emit odor and volatile organic compounds for days. Also, sanding dry polyurethane creates fine dust that can irritate lungs if inhaled without a mask, but that is a dust hazard, not chemical toxicity. New polyurethane foam in mattresses can off-gas for a few days after unpacking but is considered safe after that, especially if CertiPUR-US certified. So once completely cured and off-gassed, polyurethane is not toxic, though sensitive individuals may still prefer natural alternatives.