I used some boric acid for fleas, I didn't vacuum it up as well as I should of under the computer table. Over time I started to notice that the flesh around my big toe and second toe was starting to peel. It took over 3 years for it to finally heal up. Not that it was painful especially but definitely destroyed the skin some layers deep, anecdotal yes, and its not borax, it was boric acid over the counter from the drug store. And It did say vacuum it up completely which I didn't. It was my fault, but if you are mixing boric acid with your flux just be a bit careful with it. below is a site with the low down on boric acid and stuff. The site I got it off of for fleas says its a "non-pesticide" http://www.pesticide.org/boricacid.pdf