The aluminum salts contained in most conventional deodorants regularly disturb their possible adverse health effects on the bench. More and more suspicious, preferring rather to prevent than to heal, then turn to a natural stone, the stone of alum .

But is the latter as harmless as one imagines? Indeed, although the aluminum content appears to be less in the natural alum stone than in conventional antiperspirants, its long-term safety is not yet proven. And if the followers of the product are legion, some sensitive skins come back.

Emilie Jolibois, an expert on cosmetic ingredients research at Aroma-Zone, makes us relativize: if this mineral also contains aluminum sulphates, penetration into the skin - and thus the dangers - would be virtually non-existent.

The alum stone, what is it?

Known and used since Antiquity, the stone of alum is a natural stone, which indeed contains aluminum. In fact, it is a double sulphate of aluminum and potassium (Potassium Alum). It is found in several forms: either it is natural and then presents itself in the form of a recrystallized ore after extraction of quarries (it is also found to be sold as a powder); or it is called "synthetic" or reconstituted. In the latter case, it is no longer composed of Potassium Alum, but of aluminum and ammonium sulphate (Ammonium alum).

Naturally astringent, it clogs the pores and sweat glands and mechanically limits sweating and, in fact, the odors linked to the latter. It should be moistened before applying it to a clean, dry armpit.

Alun: incompatibilities with certain skins

If it is well tolerated most of the time, some sensitive skins can however be irritated by the alum stone.

This is the experience Elodie experienced: "I used a stone of natural alum for more than a month, the first 15 days, I was very satisfied. not as much sweat as a classic antiperspirant but no annoying odor has been reported even after a stressful stroke or with high temperatures. " "After a good month of daily application, my armpits began to itch, and I realized that the armpits had become very dry and covered with red and rough patches. immediately stopped using it to go back to the hygiene products sold in the trade.I took 15 days to find sweet underarms. "

A mishap little surprising given the drying properties of this stone, also known for its anti-bacterial and hemostatic qualities.

Is the aluminum contained in the alum stone dangerous?

This is the question that one has the right to ask when one knows that several studies warn against the aluminum salts contained in deodorants from the cosmetic industry.

"Unlike conventional deodorants that contain aluminum chlorohydrate , the alum stone contains aluminum sulphates," says Emilie Jolibois. However, aluminum chlorhydrates have been studied and pointed out in recent years.

Wrong? Not necessarily, simply, "one is not really sure that these substances penetrate in quantity in the skin." And the expert to relativize: "Our food contains a lot of aluminum also ..."

Aluminum salts: insufficient toxicological studies

In 2011, faced with a lack of quantitative and qualitative studies on the long court, the National Agency for the Safety of Medicines and Health Products (ANSM) commissioned a study: "The assessment of the risk linked to the use of aluminum in cosmetics ". This is carried out at the same time on healthy skins and on injured skins - after shaving. However, the results remain insufficient to determine with certainty any health risk.

The ANSM finds, on the other hand, that the presence of aluminum in the blood is higher when the skin is sensitized before application. To date, it recommends "not to use cosmetic products containing aluminum on injured skin". However, it does not prohibit the presence of aluminum salts in deodorants but recommends a rate of 0.6% of this substance per product, in order to avoid systemic risks.

For Dr. Alain Pineau and Dr. Olivier Guillard, who studied the dangers of aluminum and published in December 2013 an eloquent scientific article in the journal " Journal of Trace Elements in Medicine and Biology" , this substance, which would cross the barrier skin, must be decreased in cosmetics. According to all logic, they also apply this reserve to the alum stone, considering that it also contains aluminum.

Deodorant: other natural alternatives

If the alum stone, rented for its natural and ecological qualities remains an alternative to the classical deodorants appreciated, it is not however the only way to discard industrial deodorants and antiperspirants.

"If you want to avoid aluminum, you can use other active ingredients than alum, such as Bacti-Pur to dilute in a hydrosol or an aqueous solution or baking soda, " explains Emilie Jolibois. Used pure under the armpits or integrated with home deodorant recipes, this active neutralizes the bacteria responsible for bad odors.

Failing this, more and more cosmetic brands, natural but not only, offer versions "without aluminum salts" of their deodorant. They are available in organic stores but now also in large and medium-sized stores and in pharmacies, at all prices.