Alum stone: a truly natural deodorant? Composition, effectiveness, and how to use it
Alum stone has seen a spectacular resurgence in interest as consumers question the composition of conventional deodorants. Here are the clear answers.
What is alum stone?
Alum stone is a natural mineral extracted from the soil, formed from double sulfate of aluminum and potassium (potash alum). Used since antiquity in oriental beauty rituals, it possesses astringent, bacteriostatic, and hemostatic properties.
The great confusion: natural alum vs. aluminum chlorohydrate
It is important to distinguish between two radically different substances:
- Potash alum (natural stone): natural mineral, bacteriostatic action (anti-odor), molecule too large to penetrate the skin and no evidence of risk
- Aluminum chlorohydrate: synthetic salt, antiperspirant (blocks perspiration), documented transcutaneous penetration (scientific debate ongoing)
Natural alum stone does contain aluminum in its chemical composition, but in an ionic form too large to cross the skin barrier (unlike the synthetic aluminum salts in conventional deodorants).
How to use alum stone correctly
- Apply only to clean, damp skin, after showering, before drying armpits
- Slightly wet the stone under water if necessary
- Apply in circular motions for 20 to 30 seconds on each armpit
- Let air dry, do not rinse
- Store the stone after drying to prevent it from dissolving
Its other uses
- Aftershave - natural styptic, stops micro-cuts
- Facial care - tightens pores after cleansing
- Feet - effective against odors
Frequently Asked Questions
Does alum stone contain dangerous aluminum?
No. Potash alum (KAl(SO₄)₂) is a molecule too large to penetrate intact skin. Current toxicological studies show no significant skin absorption.
Is alum stone suitable for sensitive skin?
Yes, its simple mineral composition is ideal for people allergic to the components of conventional deodorants (fragrance, alcohol, preservatives).
What is its lifespan?
A 120g stone lasts on average 12 to 18 months depending on frequency of use.
