Formaldehyde is a common chemical in building materials and household products. The chemical is also found in glues, and permanent press fabrics. Most people recognize formaldehyde as a chemical used in mortuaries and medical laboratories. Long-term exposure, such as through the air, has been linked to leukemia, nasal cancer and nasopharyngeal cancer. It was officially classified as a known carcinogen in 2004 by the International Agency for Research on Cancer. Formaldehyde is known to have effects on some people who are only exposed for a short length of time. Those symptoms include watery eyes, coughing, wheezing, nausea and skin irritation. Many people have no adverse reaction to formaldehyde at all. Many homeowners unknowingly had high formaldehyde levels in their houses, at least deep in the walls. Urea-formaldehyde foam insulation was popular in the 1970s but is not widely used now. The most common exposure in the home would come from pressed wood products and kerosene heaters.