Formaldehyde is widely present from the universe to a single cell. It also comes from our daily life, including food, water, clothing and building materials. As a main material or by-product from industrial and commercial production, formaldehyde is the most common aldehyde in the environment. The most common formaldehyde exposure is from contaminated air. In general, human beings spend around 90% of their time indoors, where there are complex mixtures of pollutants, including formaldehyde. Indoor formaldehyde exposures can be extremely dangerous, such as residential exposing to renovated homes, offces and public shopping centres. Another main method of formaldehyde immersion is through occupational exposure, for instance, in some factories, hospitals and laboratories, where formaldehyde concentrations are much higher and the people working there are highly vulnerable. Although the toxicity of formaldehyde has been extensively studied and its detections have been well developed, the exposure of formaldehyde is still serious all over the world, especially the countries that are producing and consuming huge amounts of construction materials which contain and emit aldehydes. People are exposed to formaldehyde through breathing and gastric intestinal digestion or by skin contact. The exposure to formaldehyde can cause respiratory irritation, asthma, tumours and multiple neuropsychological abnormalities or even cause death. Therefore, it is of great importance to control possible sources of formaldehyde and set up international standards to avoid formaldehyde insult.