Formaldehyde is a colorless, flammable gas that can be carcinogenic to humans, and is a common additive to building materials and household products. Formaldehyde is also formed in the environment upon oxidation of a variety of hydrocarbons, including natural gas (methane). Symptoms of exposure to low concentrations of formaldehyde may include headache, nausea, throat and skin irritation, and exacerbated chemical sensitivity. For a quick summary of formaldehyde exposure basics, please see the ASTDR’s ToxFAQs for Formaldehyde. For much more in-depth information, please see the ASTDR’s Toxicological Profile for Formaldehyde.