My understanding is that EVERYONE will eventually become sensitised to epoxy if exposed. It's just a question of how much exposure it takes.

Once sensitised, you can forget about working with it ever again without major protection, and in severe cases, even touching a 'cured' epoxy surface can set off a reaction.

As has been said, respirators are cheap, overalls are cheap, gloves are cheap, so really, why would you not protect yourself?

Also remember that the same applies when sanding epoxy - there will be small amounts of uncured, or partially cured epoxy in the dust, and that is just as bad for you.