Tea Tree Oil - Although it's relatively safe when diluted, make sure you never use tea tree oil undiluted. It's basically an insecticide/bactericide manufactured by the tree to protect itself. In undiluted form it can burn skin or cause an overdose. Products that have less than 1% tea tree oil are not bad, but the smell is really awful to a dog. They take care of bacteria, but that's not really the problem. The real problem is too much histamine causing inflammation in the skin cells and sending itch signals to the brain. Tea tree oil and it's relatives are very good at killing germs but itching and inflammation isn't caused by germs and the smell is way too intense for dogs.
With Borax it’s all chemistry, and the way they try to manipulate those who aren’t as proficient in chemistry is beyond greedy and shows ulterior motives[those being it’s not as ‘profitable’ for big corporations to market it which is why ‘laundry detergent’ is so expensive… Chemical companies profit more from synthetics than natural substances. Natural borax is even used in homemade ‘cold cream’ recipes and skin care. It is not harmful unless you inhale it into your lungs.. Incidentally, sodium ‘bi’carbonate [baking soda which is non-toxic and edible] can be made into washing powder [sodium ‘carbonate a bit toxic if ingested] just by heating it in the oven at 140F/60C until it becomes dull and opaque [this is how I make my own since the shops here don’t have actual ‘washing powder] All it is, is a removal of the water molecules and you got yourselves a different chemical. But it is still safe when used according to it’s purpose!! Just don’t eat or breathe it in it’s caustic forms and you’re ok [common sense, really…]