Formaldehyde is one of the most commonly used chemicals in the nation. It’s used in wood composites in furniture and cabinets, as well as in cleaning products and cosmetics, and is spewed into the air by oil refineries. Formaldehyde can be inhaled as a gas or vapor or it can be absorbed through the skin in liquid form, according to the National Cancer Institute. The federal Centers for Disease Control says that formaldehyde is “known to cause cancer.”