Formaldehyde is a very dangerous chemical if inhaled or ingested in any sort of way into the body. Products and things that release Formaldehyde are car exhaust, pressed wood products, tobacco smoke, secondhand smoke, and hair smoothing treatments. Scientists have done many studies that say that inhaling or being exposed to formaldehyde for too long can lead to cancer. They have tested it on rats and it led to cancer people that have been exposed to a lot of formaldehyde have reported a higher risk of Cancer of the nasopharynx.