Formaldehyde is known as a human carcinogen (cancer-causing substance) by the International Agency for Research on Cancer, and as a human carcinogen by the U.S. Environmental Protection Agency(EPA). Formaldehyde in sidestream cigarette smoke is evident in concentrations of up to three times above occupational limits, which readily accounts for eye and nasal irritation.

Formaldehyde is also found in embalming fluids used to preserve bodies and lab specimins. That frog in the jar at school is floating in formaldehyde.

The tobacco industry uses formaldehyde in order to preserve tobacco moisture. Yummy.