That depends entirely on the resin. Some are toxic, some are sensitizers, some are irritants. For the latter two, your sensistivity may vary.
Good rule of thumb: If you can smell it, you shouldn't.
I've noticed that most commercial suppliers of resins are now quite happy to provide you with an MSDS (Material Safety Data Sheet). It's a good idea to get these, read, and undestand them. If you are not sure what they mean, e-mail me and I'll be glad to help.
See "Good rule of thumb" above.
Reread "Good rule of thumb" above.
ibid.