~ World Almanac and Book of Facts, 1916
Though it’s a known carcinogen, formaldehyde is more common than one might think. It’s even a [very transient] structure in some processes within the bodies of vertebrates, though formic acid is more common.
When you’re exposed to formaldehyde in the environment over long periods, it can cause nasopharyngeal cancer and some forms of leukemia. Though it’s not the primary preservative in most current zoological or biological specimens, older ones are still often kept in it, and this can cause some exposure in students if proper safety precautions aren’t taken. The safety is easy enough though, and there’s little risk for people who don’t encounter it every day.
Everyone knows its toxicity and that you can die from it if there’s too much exposure, but when you don’t get exposed to enough to die, why do you feel so sleepy and confused and stupid-like? Well, formaldehyde breaks down a major carrier protein in the body, serum albumin.
When serum albumin is broken apart and its internal structure is exposed, it can’t do its jobs, which include: transporting drugs, transporting thyroid hormones, maintains osmotic pressure, and transports any fat-soluble hormones it encounters.
For those interested in chemistry, formaldehyde is quite interesting. It’s the simplest aldehyde out there, and is known by its systemic name “menthanol”, which, if you fuck up in lab and confuse with “methanol”, does not do remotely the same thing, and will greatly piss off your lab partner.