I have not experienced any, not even close to a negative reaction with borax. Borax consist of natrium, boron,hydrogen and oxygen ; it is found in nature; as a matte, whiteish crystal.
Boric acid is a different story; it is the acid variety of borax, used as a vaginal douche for candida /thrush. I have never used the acid; it is much more toxic.
Borax is so mild it can be used in the eyes. When my 9 year old swim in a chlorinated pool; he gets very sore eyes; red, stingy, burning eyes. a mix of borax and water takes away the pain right away (one or two drops in the eye), probably because of the alkaline quality of the borax.
Israel has a very low rate of arthritis; their ground / water has natural high content of borax. Norway is full of Arthritis and also full of people with candida related ailments + fluoride related ailments. Borax is an antidote to fluoride; and also very effective weapon against candida. Works very well with iodine.
My latest experiment with borax also involves one of my kids. He has suffered from frequent urination from when he was little; and I have tried everything to help him ( I am educated as a homeopatic doctor ) One month ago I tried some saw palmetto and for the first time also a little borax. (suspected a fungus origin for this ) It worked right away, same night he didnt have to get up to pee; the next week he was all fine. Then I went away for a 3 weeks working trip. When I came back his problem was back full strenght, even with using the saw palmetto. Then I realised it was the borax that have had effect. I gave him one capsule two days in a row; and problem gone again.
He has probably inherited my candida problem.
More later.. have to make them some lunch..