^^ i wouldn't want to inhale a big cloud of corn starch. my ex-wife has a lot of degrees and certificates in this area, and she says it's bad to inhale ANY particulates... this would include corn starch and talcum powder, asbestos, diesel fumes, cigarette smoke, etc. some particulates are worse than others, and some can be dealt with by the body better than others, but really, just avoid inhaling particulates, even if they're "natural".

if i was going to spend more than a few minutes in a cloud of talcum powder, or corn starch, i'd get an appropriate mask/filter. otherwise, i wouldn't worry about it.