Use a brush or wear disposable gloves long term exposure is not
good. It is a poison.
Let's try to be a bit realistic. Kitchen salt is the other example
given in this article. Salt is lethal as well, do you wear
respiratory protection and rubber gloves when baking?
Taking the numbers from the article, the LD is 5 to 20 g/kg. That
means 350g (12oz.) to 1400g (50oz.) for me. I might be crazy at
times, but would you imagine someone eating so much boric acid?
Anything is lethal in a high enough dose.