Is borax toxic to cats?

I have used borax to successfully treat a flea infestation in my house. I have 13 cats and 4 dogs and none have had any ill effect from the borax. I have not left it on the carpeting for more than a few hours before vacuuming it up again, however.

The MSDS (material safety data sheet) for borax states "WARNING! HARMFUL IF SWALLOWED, INHALED OR ABSORBED THROUGH SKIN. CAUSES IRRITATION TO SKIN, EYES AND RESPIRATORY TRACT. "

I would err on the side of caution and not use it directly on your cats.