No Sweat - Potassium Alum

Welcome to the third in this mini-series about deodorants and what makes them tick. Now that you know all about what exciting things go on in armpits and are familiar with the basic makeup of a deodorant (if not, find links below), we're going to start focusing on the different active ingredients – the ones that make a deodorant do what it is supposed to to de-odorise!

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.

What is it?

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.

Where's it From

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 occurring 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 Deodorise?

In a word, yes. However (there's almost always a however, isn't there?) – potassium alum can't carry a full day of deodorising 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 deodorising 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. 

Speaking of Which

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 Other 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

Do Tell

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.


Anonymous said…
Hi Lise!

I am a longtime 'lurker' on your excellent blog. Most of the DIY baking soda-based recipes use baking soda, which is pure sodium bicarbonate - not baking powder, which is sodium bicarbonate plus acid salts (including aluminum salts).

I've wondered about why people get when they use baking soda deodorants (including LUSH's discontinued Aromacreme)... I have a couple of guesses: the first is that baking soda is so abrasive that delicate underarm skin just can't take it after a while; and my second guess is that you end up with little granules of sodium bicarbonate all over your skin, so that when you sweat, you have a locally saturated alkaline solution (pH 9 or more, it seems?), which irritates skin after a while. I'm curious to know what you think of these guesses!

Thanks for your great blog!
LisaLise said…
Hi 'Lurker'. Thanks so much for your input and positive words! You are absolutely right about baking soda/powder. In my initial searches on this, I kept running across information that basically places baking soda and baking powder in the 'same drawer'. I have as yet to get down and dirty in my research of the chemistry of the baking soda deodorants, but I suspect you are quite right with both of your theories on why they are so abrasive.

This is now officially on my to-do list - find out exactly what it is that causes the abrasive reaction to baking soda deodorants. I will dedicate a post to this soon. Thanks again!!
Anonymous said…
Thanks, Lise! I look forward to your post!!
Noaa said…
I have been using Baking-soda based deodorant. I've heard from other people that the rash is mainly caused by the corn starch. After hearing that i switched to using arrow root powder, which also makes the deo. softer and creamer (no lumps! :) ), and haven't had the rash problem or irritation. The only irritation i get is when i shave and then immediately apply deo.
I noticed the plain deo works quite well at blocking and absorbing odors for most of the day but if you add clove E.o. it works for the whole day and clear into the evening. Even if you go to the gym after work.
LisaLise said…
Oooh thanks Noaa! This is great input. I will have a serious look at this while I am researching the baking soda.
Also, clove EO can be a skin irritant.. but I'm guessing you are using a very low dose..? (I imagine the scent is absolutely divine!)
Noaa said…
Yes, alittle clove goes along way! I may also be immune to it. the only real problem I've had is that it leave alight stain on my skin (most of it washes off when i shower) after using it for a could of months.
Heather said…
I have also read that it is the cornstarch that causes the rash, because it is very yeast friendly. I have recently started using homemade deodorant, and my left armpit has a rash. I would assume that both arms would have a rash if I was reacting to the ingredients themselves, but my rashy pit looks a lot like the splotchy yeast infection my son got one summer while he was still in diapers.
LisaLise said…
Hi Heather - thanks for your input. That's another one I actually have on my to-do list-- check out the pros and cons of cornstarch in deodorants. From your experience with it, it sounds like you may just be right about the yeast-friendliness.
Anonymous said…
Interesting Lise. I was just doing a google on it as I was thinking of applying to with aloe juice to my dogs legs to keep him from licking. (tastes terrible). I know it's used to heal cancer sores in the mouth also. I think it might be too irritating for the doggie legs....
Anonymous said…
Interesting Lise. I was just doing a google on it as I was thinking of applying to with aloe juice to my dogs legs to keep him from licking. (tastes terrible). I know it's used to heal cancer sores in the mouth also. I think it might be too irritating for the doggie legs....

I used to make a great deodorant with Chitosan. You have to get it to an acid pH to liquefy. Works well though.
LisaLise said…
HI Rebecca -

Thanks for your input! Interesting idea with the aloe and potassium alum for your dogs! I've actually never heard of doing this before and wonder how it goes for you. Please do keep me posted!

As to the Chitosan - I'm not sure as to how this is an effective deodoriser? I only know it as a medical application. Could you elaborate on how you used it?
LisaLise said…
Rebecca - I just came across information (on the ASPCA site) that says aloe is toxic to dogs! Please do some research on this before you try it on your pets!
Anonymous said…
I have fallen to the nasty pit rash left behind from using a baking soda based product. I wish I would have found your site first! I thought it was a reaction to the essential oil that I used so I made another batch with different essential oils - after I had nursed my pits back - only to use the new batch one day and the rash is back!!! Going to try your recipe.
LisaLise said…
Hi Anon - Oh I'm so sorry to hear you have had a skin reaction from baking soda deodorant. I really hope you heal quickly and that my recipe is of help to you. Thanks for sharing.
Unknown said…
I made a diy deodorant based with baking soda...does it work? Yes! Do I have massively painful puss filled pimples and sores? Yes :(
LisaLise said…
Oh Ashley I'm so sorry - I hope your pits heal quickly. If the rash and bumpiness doesn't heal quickly, it might be a good idea to see your doctor.
Unknown said…
Hello Lise, some people use powdered aluminum alum in lotion making for lightening, how safe is this and is it really effective?
LisaLise said…
Hi Judie - painting a mixture of alum and honey onto the face to whiten the skin was popular in the 1500's, but I'm not sure how effective it was. The folks you say are using this in lotion - are these DIY'rs? I can't find anything science-based on this, so already a little red warning flag pops up for me. I'll be doing a bit of research on this and may put it into an upcoming post. Thanks for bringing this to my attention.
Anonymous said…
I have been using baking soda deodorant for years. A few notes -
1. I only get irritation when I use it just after shaving...and sometimes in the middle of an extra hot and sweaty summer.
2. Baking soda works ok. Coconut oil works a little. Together they work wonderfully. Normally I use them mixed together into a convenient stick.
3. Shaving irritation is prevented by rubbing coconut oil onto armpits first, then patting on a little baking soda on top. This protects the skin from the baking soda. For the summer irritation, this seemed to result in happy skin where the coconut oil had been applied, with a ring of redness around it.
4. This seems to support the theory about baking soda making a high-ph solution when mixed with sweat. Maybe heavier sweaters are more prone to reactions than lighter sweaters like myself?
LisaLise said…
HI Anon, thanks for your input. I'm glad you have found something that works for you. I have received so many different accounts from people who have had reactions to baking soda deodorant. Unfortunately, using coconut oil as a 'protective layer' doesn't seem work for everyone. I also continue to get comments and mails from people who don't have any reaction to baking soda as deodorant until after several years of use. I hope your method continues to work for you and wish you the best. :)
Amelia said…
Hello Lisa,
Love your site and all your worthy information.
I want to know more about the safety of Potash alum, is it completely safe. I am not able to find much information about it. As aluminum salts are mostly not safe. I was recently gifted with this substance, please let me know.
LisaLise said…
HI Amelia,

Potash alum is the same as potassium alum. It has various common names.