Formaldehyde (systematic name: methanal) is an organic compound with the formula CH2O. As the simplest aldehyde, it is an important precursor to many other chemical compounds, especially for polymers. In 2005, annual world production of formaldehyde was estimated to be 21 million tonnes (46 billion pounds). In view of its widespread use, toxicity and volatility, exposure to formaldehyde is a significant consideration for human health.
Formaldehyde is more complicated than many simple carbon compounds because it adopts different forms. Formaldehyde is a gas at room temperature, but the gas readily converts to a variety of derivatives. These derivatives generally behave similarly to gaseous formaldehyde and are used in industry. One important derivative is the cycle compound trioxane, the "trimer" of formaldehyde with formula is (CH2O)3. When dissolved in water, formaldehyde converts to H2C(OH)2, a diol (i.e. a compound with two hydroxy groups). Aqueous solutions of formaldehyde are referred to as formalin.