When I handle hemlock bark mulch with my bare hands, they hurt after a short time, usually for the rest of the day. This doesn’t seem to happen to anyone else I know, and it doesn’t happen when I handle cedar mulch. Just how toxic is it, and do many people have problems like this?
Eh, I don’t see anything offhand, so I’d guess that it’s just that you personally are more sensitive to hemlock bark than to cedar. Could be an allergy, could just be an irritant. It could also just be a mechanical irritant, from prickles. Wear gloves?
There are (at least) two different plants with the common name hemlock; one of them is an umbelliferous (carrot family) herb that looks a bit like Angelica and Cow Parsley; this is the famously deadly plant from which the poison was extracted to kill Socrates.
The other is a conferous tree which is not especially poisonous - this is the one from which your mulch is made. Sounds like you have an allergy to it (or something(mites, fungus etc) that lives on it).