It actually isn't bad for you, since the fumes become inert upon contact with moisture. (in your nose, eyes, etc.) They are, however, an irritant - and some people can be allergic to them.
(Maybe someone here can do the whole C5H5NO2+H2O equation.. Years ago I would have been able to, but I can't now
)
So while it can smell nasty and irritate the hell out of your eyes and nose, it's very unlikely that it can actually cause you harm.
So while cyanoacrylate fumes are NOT toxic, remember that ANY irritants can cause 'ideopathic' allergic reactions, (allthough rare--) as well as the possibility of secondary triggers causing a latent allergic reaction. (Even if you've never had an allergic response before. Allergies are generally not 'genetic', and can begin for anyone at any time.) If at any time, (with ANY possible irritant -- solder fumes, glue, plastic, anything) you start to feel your throat closing up (Even a little) , or your tongue swelling, DO NOT "wait around" to "see" if it's an anaphylactic reaction. Call help RIGHT away, and take an antihistamine such as benadryl/diphenhydramine while you're waiting for them to come.
Not to scare you. That's just good sense from working with any possible irritants, from onions to epoxies.
Also, take what AUTO XX said about the reaction with cotton seriously: If you're wearing cotton clothing and working with cyanoacrylate, a drop of it on that cotton clothing can cause an exothermic reaction that can burn your skin severely (and compound it by bonding the burnt material to your skin) or even set clothing on fire. (Really.)
So, generally, cyanoacrylate is rather safe even though its fumes can knock you on your butt. Just be aware of what can happen, and respect the materials...
