Should you be for or against Alum stone?

By the 07 November 2019

Modifié le 07 November 2019

Alum stone is thought of as a healthy alternative to conventional deodorants that are normally full of aluminium salts. Are they really better or is this just what we’ve been told? What if Alum stone isn’t as good as we think it is? Before we trust it on our armpits, let’s have a closer look at it. 


Is Alum stone the perfect deodorant?

Alum stone has a very reassuring name, doesn’t it? It sounds VERY natural and doesn’t seem to imply anything controversial at all. We thought it was going to be a refuge for our armpits when we found out about the harmful effects of conventional deodorants.

Alum stone is from mineral origin and has a lot to offer when it comes to our fight against sweat patches and bad smells. It’s very effective – antiseptic against odorous bacteria, slightly astringent to gently regulate excessive sweating without stopping it completely and remains effective for several hours, even in high temperatures. It’s rarely irritant, doesn’t cause allergic reactions, has no scent, doesn’t leave marks on clothes and is very simple to use: apply it dampened to your armpits – that’s it! When it comes to practicality, it can easily be taken with you and and you can take it through airport security. It would be difficult to find a more sustainable option: one stone, that doesn’t need a lot of packaging, lasts for years. Of course it’s just an added bonus that it’ll look very pretty in your bathroom with its crystal-like appearance. It sounds like we’ve found the perfect solution.


A not so natural stone…

Already putting on your shoes to go and search for your future deodorant in the mountains? Not so fast! It’s name is rather misleading: Alum stone doesn’t actually exist in raw form in nature. It turns out our miracle deodorant isn’t so natural after all… it could even be classed as borderline greenwashing.

You’ll find 2 types of Alum stone in shops. 100% synthetic Alum stone, made entirely from ammonium alum or even from synthetic ammonium sulfate, a byproduct of the nylon chemical industry. This is far from the idea of a naturally occurring stone you could pick up from the side of the road. These synthetic stones are generally what’s found in deodorants that are labelled as being Alum stone based. In fact they’re actually antiperspirants – that’s what Alum stone does… and antiperspirants aren’t so good for your health (To find out more, see our article: Antiperspirants and deodorants: what’s the difference?).

Even the kind of Alum stone that is advertised as being natural isn’t truly natural. To manufacture it, rocks rich in Potassium alum (bauxite, Alum-K, kalunite, alunite) are extracted from mines, often in China, which are often socially and ecologically disastrous. They then undergo several chemical treatments to extract, purify and then recrystallize the aluminium crystals. They’re then heated for several days at very high temperatures to get rid of impurities then put into water for several months to make it porous. The crystals are then filtered and cut and polished. Not such an eco-friendly process!


So you know what to look at for, the natural Alum stones are called Potassium alum. They are more translucent than synthetic stones that are known on INCI lists as Ammonium alum or Aluminium alum. The whiter an Alum stone is, the more synthetic it is.

Alum stones: time to throw them away?

In reality, it doesn’t really matter whether they’re synthetic or pseudo-natural. All alum stones have a hidden vice: aluminium. Alum stone’s miracle effectiveness is attributable to aluminium salts… oops! The option that was just presented as being an alternative to conventional deodorants and antiperspirants contains a controversial ingredient. The problem with aluminium salts, is that they’re suspected of causing breast cancer, hormone troubles, degenerative diseases and anemia amongst other things (to find out more, see our article: Effective and safe deodorant with natural active ingredients: how can you avoid aluminium salts?). It’s starting to sound like it’s not such an ideal deodorant…


Whether you use a 100% synthetic stone or a more natural one, you still leave aluminium on the skin and the National Agency for Drug and Health Product Safety recommends avoiding synthetic Alum stone at all costs. More natural stones are said to not pose the same risks, although the harmfulness of their aluminium salts haven’t yet been proven. Manufacturers stress that the amount of aluminium actually deposited on the skin is below the recommended limit and that Potassium alum isn’t absorbed by the skin due to its molecular structure and its negative ionic charge. However they still recommend that you don’t use them when the skin is very permeable, after shaving, waxing or if you have any cuts… Hmm.


What should you do then? When faced with a conventional deodorant full of aluminium salts, synthetic perfumes and preservatives, it is of course better to use a so-called natural alum stone. However, as a precaution, we advise that you avoid ALL alum stone, particularly during pregnancy or if you are experiencing kidney problems. If it was found that the aluminium was actually entering into our bodies, it’s true that it would only be in small quantities, but they’re daily and applied to an area of skin that’s particularly permeable. We are also exposed to many other sources of aluminium everyday, notably through our diet. 

In short, we might as well avoid adding to our aluminium exposure where we can. It’s made even easier by the fact that natural, effective and safe natural deodorants do exist. Your armpits can be natural and odorless without aluminium salts. It is possible!

This post is also available in french.


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