I am a retired chemist and have used boric acid and borax extensively, in the lab and as supplement, both oral and topical. Though extensively used as an effective ant poison when mixed with sugar, boric acid is quite safe and non irritating, indeed having been used for decades as an eye wash. Similarly borax is basically boric acid with a lot of sodium. Both contain boron about 22% for boric acid versus 11% for borax. And oral borax is instantly converted to boric acid in stomach acid. Contrary to medical hype attempting to block its use as an effective arthritis remedy in Australia and Europe where sales are banned, it is about as toxic as common salt and widely used baking soda in antacids.
The major problem is high sodium in borax for persons on low salt diets. Luckily it can still be bought also as fairly pure 20 Mule borax for use as an excellent detergent enhancer and an arthritis remedy at about 1/4 teaspoon borax or hard to find pure boric acid, best USP or NF grade, in quart of water taken in small portions over about 16 hrs. Google The Borax Conspiracy to get the facts and disregard medical hype seeking to outlaw this arthritis remedy, another miracle drug like aspirin.
Also chelated boron sold as 3 mg capsules may not be as effective.