formaldehyde, methanal, formol, methyl aldehyde, methylene oxide, oxomethane Formaldehyde is a colorless gas with a strong smell that polymerizes spontaneously into paraformaldehyde. It is usually stored in aqueous solution (called formalin). Formaldehyde is toxic (carcinogenic) and very volatile but sees widespread use (especially in production of industrial resins). H301H311H314H317H331H335H341H350H370P201P280P303+P361+P353P304+P340+P310P305+P351+P338P308+P310