How Potassium Alum Works in Our Crystal Deodorant Classic
Door Salt of the Earth
If you've started reading deodorant labels, you've probably spotted "potassium alum" on the ingredients list of our Crystal Deodorant Classic. It's a simple ingredient, but it does a clever job. Here's what it is, how it works, and how it differs from aluminium chlorohydrate, the ingredient found in products designed to block sweat.
What Is Potassium Alum?
Potassium alum is a naturally occurring mineral salt [1]. Its full chemical name is potassium aluminium sulfate, sometimes called alum stone [1]. People have used potassium alum (and a close relative, ammonium alum) as an underarm deodorant for a long time, across many different cultures, including in Europe, Mexico, Thailand and the Philippines [5]. It isn't a new idea. Salt of the Earth has used potassium alum since we launched our original crystal deodorant back in 1993 [10]. It's the ingredient our Crystal Deodorant Classic is built around, and it hasn't changed since.
How Does Potassium Alum Stop Odour?
Body odour comes from bacteria on your skin [4]. When you apply potassium alum, it sits on the surface of your skin as a thin layer [2][3]. From there, it works against the bacteria that cause underarm odour. A lab study testing potassium alum against these odour-causing bacteria found it stopped their growth, working from a concentration of 7.5mg per millilitre upward [4]. That's the whole job: fewer active bacteria on your skin means less odour.
Why the Crystal Format Matters
The Crystal Deodorant Classic is a solid block. You dampen it with water and rub it gently onto your skin. This is how the thin surface layer forms in the first place [2][3]. There's no spray, no stick residue, just a light, even layer of potassium alum sitting where it needs to be: on the surface of your skin.
Potassium Alum vs Aluminium Chlorohydrate: What's the Difference?
This is the question most people want answered. Potassium alum is made of bigger particles that can't get through skin [2]. Aluminium chlorohydrate, the ingredient used in many products designed to block sweat, works differently. It's made of tiny particles, small enough to get into your sweat ducts [6][7]. Once inside, these tiny particles get into the duct and block it up, near the surface of your skin [6]. Only particles this small can do that [7]. Potassium alum simply isn't built that way, so it can't block anything, it stays on top of your skin instead [2][3][7].
