Today's star is a staple in my stock and present in all of my deodorants. Its chemical formula is shown above. It belongs among the privileged few ingredients that have a pronounceable INCI name: Potassium Alum.
Potassium alum is 'the potassium double sulphate of aluminum'. It is derived from the oxidation of sulfide minerals and potassium-bearing minerals. In short, it shows up as encrustations on rocks (that contain sulfide and potassium-bearing minerals) when they come into contact with air (well, not so much air as oxygen molecules, but you get the drift). You may already know these encrustations as 'natural crystal deodorant', because potassium alum is shaped and sold in solid form as such.
Potassium alum is naturally occurring and can be found all around Europe, North and South America and parts of Asia (check the pictured map for potassium alum hotspots).
Can it Be Made Synthetically?
Yes, it can. As far as I understand, you have to be a fairly mineral-savvy person to distinguish a synthetic potassium alum crystal from a naturally occuring one. Synthetically made crystals will have a different opacity due to the presence of aluminum hydroxide.
So What's The Diff?
Naturally occurring potassium alum is preferred for cosmetics use because it has no aluminum hydroxide. The synthetically made crystals can be a mild skin irritant due to the aluminium hydroxide content.
Does it Deodorize?
In a word, yes. However (there's almost always a however, isn't there?) – potassium alum can't carry a full day of deodorizing action all by itself. If you don't mind applying deodorant every few hours, it's fine. But I do mind. Therefore, I combine it with other actives to create a deodorizing cocktail that works as long as a commercial deodorant.
You Can Eat it Too
Potassium alum is used in various areas (among these: water purification and leather tanning) but you may very well already have potassium alum on your kitchen shelf. Can you guess where? Potassium alum is used as the acidic component of some baking powders.
There are several recipes around on how to do a simple DIY baking-soda based deodorant. These deodorants are reported to work, but are unfortunately also often accompanied by a skin reaction after a short period of use. I've read accounts of everything from a mild redness to serious rash forcing the person to stop use (with subsequent nursing of armpits for a period of time). I have a sneaking suspicion that it is the presence of aluminium hydroxide and sodium aluminum phosphate (or perhaps even some of the other more acidic components found in baking soda) that could be the culprits. Sodium aluminium phosphate is produced from aluminium, phosphoric acid and sodium hydroxide and is not allowed for use in foodstuffs in Japan and some European countries due to its aluminum content. Despite also reading many positive accounts on how well a baking-soda deodorant works (if you can get past the almost inevitable period of rash and irritation), I'll readily admit that I would want to do a bit more research into the specific components of baking soda before feeling comfortable about giving this a try.
Find The Previous Posts in This Series Right Here
No sweat - how does deodorant work
No sweat - the basic make-up of deodorant
Updated post on Potassium Alum
Have you ever made and used a DIY baking soda deodorant? Did it work for you without any skin irritation?
Please see an updated post on potassium alums deodorizing capabilities here.