Originally Published on Chemical of the Day blog March 8, 2010. Updated 4/10/22.
The subject of aluminum in crystal deodorant stones has sparked a lot of controversy since I published my first article, and it has even started a bit of a Twitter war with a crystal deodorant company.
After calling my article "misleading and irresponsible," they stated that "there are two types of aluminums, processed or naturally occurring." They go on to describe how the anti-perspirant compounds like aluminum chlorohydrate and aluminum zirconium are synthetic and harmful: "Because processed aluminums have a very small molecular structure, the concern is that it will penetrate the skin and can be a potential problem for people who have kidney issues." They tout the safety of their product, stating that the alums they use in their product are "natural mineral salts and are forms of naturally occurring aluminum" and that they don't pose a risk because "alum molecules are too large to penetrate the surface of the skin."
So, let's take a look at this.
Aluminum Chlorohydrate has a molecular weight of 174.45
Okay, now let's look at alum. When alum (full name, Potassium or Ammonium aluminum sulfate) is in its solid crystal form, the molecules create a crystalline structure. However, when it is wetted, the molecules break out of their crystalline structure and become ions (singular atoms with a positive or negative charge). So, when you're applying a wetted crystal to your skin, you're applying aluminum ions, the smallest possible form of aluminum, to your skin.
Aluminum in ionic form (as it is when dissolved in water)
An aluminum ion is much smaller than a molecule of Aluminum chlorohydrate. It only has a molecular weight of 27, whereas Aluminum chlorohydrate is 174.45. If Aluminum chlorohydrate is small enough to be absorbed, and size is a factor of absorbability, then aluminum ions definitely are. Aluminum ions are six times smaller than Aluminum chlorohydrate. And considering that our bodies are made up largely of water, and that alum is so easily dissolved in water, it makes no sense that it wouldn't be absorbed in to your skin cells and your body.
They say their product is safe and had a chemistry professor "analyze" their product. The chemist states: "Ion transport through the skin is rather rare and I would not expect it from the small amount that would rub off on your armpit or fingers while handling it." But while a chemist gave his opinion on it for them, the product and its absorption was not actually studied. They say that "there is no research to suggest that alum poses a possible health risk." But that's because there is absolutely no research about the absorption of alum, whatsoever. Thus, there is also no research to suggest that alum doesn't pose a possible health risk.
They talk about how alum is naturally occurring, but just because it occurs in nature, doesn't mean it's safe. And it's not as if their stones are really natural, either. They're not going in to a cave and digging crystals out of the ground. Alum doesn't occur in nature enough to be able to do that. Their product is being synthesized in a factory or lab, using bauxite ore, a by-product of strip-mining, and sulfuric acid. (See my previous article for more info on the process.)
I searched the government's database of health studies for everything that I could about alum and aluminum ions, and while there are no direct studies testing the absorption rate of alum, I found some interesting things.
In recent years, vaccine powders have been studied as an alternative to injectable vaccines. They've found that these powder vaccines can be just as effective and viable as an injectable vaccine. The powder vaccine is made up of three primary ingredients, a natural powder like mannitol, the active antibodies, and, you guessed it, alum. (Here's one study) In this case, even in its crystalline form, alum proves to be a potent ingredient that helps other ingredients absorb into the skin and become active in the body.
So now let's look at aluminum ions, which is really what you're putting on your skin when you use the crystal stones and sprays.
Aluminum ions are toxic to plants and animals. The crystal companies love to say that aluminum is a naturally occurring mineral from the earth, but they don't tell you that naturally-occurring aluminum in soil is problematic. Plants don't grow in aluminum-rich soils. Aluminum is abundant, but it plays no part in any biological function in plants or animals. Current research points to the possibility that aluminum robs cells of magnesium (source) a vital mineral, and that's why they won't grow.
One of the biggest problems of acid rain is that aluminum leaches (turns from a solid metal to a dissolved, ionic form) into water under acidic conditions. In streams and bodies of water that have turned acidic, plants and animals die because of the aluminum toxicity from soil leaching. (source) [And guess what that form of aluminum is? Yep, ionic aluminum, the same form of aluminum you're applying to your skin when you use a crystal.]
If you're trying to avoid aluminum in your life, you've probably decided to not use aluminum pots and pans. You know that putting acidic food in aluminum causes aluminum leaching in to the food. When aluminum is leached in to food, it turns from a solid metal, in to ionic form. This is the same aluminum ion you create when you wet the crystal deodorant stones. When they create alum, it's effectively the same process. They add sulfuric acid to aluminum-rich bauxite ore. The aluminum is leached in to ionic form, and then the resulting liquid is dried out and the remaining aluminum salt crystalizes in to the stone that you use for the deodorant. When you wet the deodorant stone, you're effectively putting aluminum in the most bioavailable form possible on your body's largest organ: your skin.
A few facts about alum:
Alum is commonly used in municipal water supply purification because it helps to remove particulate matter. However, cities have to carefully filter and monitor levels of aluminum left behind because of its toxicity.
Mice who were dosed with alum showed significant losses in memory. (Source: http://www.ncbi.nlm.nih.gov/pubmed/10437134)
This Russian study looked at alum to assess its safety in the workplace. It's classified as a class 3 moderately hazardous material and the study recommended that employers monitor the air quality for the dust from these ingredients and not to let it exceed a half of a milligram per cubic meter (Source) MSDS sheets for alum recommend that if it comes in contact to skin, to rinse skin for a minimum of twenty minutes. Additionally, during transport it's classified as an environmentally hazardous material.
People have died from eating as small as 30 grams of alum. If a shard of the crystal were to break off of your deodorant stone and a child or pet were to accidentally eat it, they would get very ill and could possibly die. Eating 1/4th of a typical deodorant stone would be the lethal dose for a normal healthy adult.