I use the witch hazel as a base because alcohol is very drying to my skin. I add a bit of alcohol to my recipe because I've read it helps keep the essential oil from separating. It seems to be true , because that's how I keep my air freshener scent mixed w/o having to shake it before spraying. I can't answer to the magnesium hydroxide because I've never tried it. Give it a shot and see what you think? If you already have it, and it turns out that it works - problem solved! Not to mention it would be one less thing to have to buy. I used the magnesium chloride because of the health benefits, and it's one of those minerals that our bodies get the most benefit from through absorption, rather than by supplement. If you try magnesium hydroxide and it works, please let us know. I bought a HUGE container of the mag chloride (the only size I found) that may last me a life time, but who knows, the hydroxide might be milder, or work better than magnesium chloride in deodorant. I'd like to know too.