Alum Stone: The Natural Deodorant Validated by Science

June 24, 2026

La pierre d'alun : le déodorant naturel que la science valide - D.Crouzet

What is alum stone?

Alum stone is a natural mineral composed of potassium aluminium sulfate (potassium alum, KAl(SO₄)₂·12H₂O). Used for centuries in the East as a deodorant and astringent, it is now experiencing a considerable resurgence of interest in the natural and zero-waste movement.

Unlike conventional deodorants, it does not contain aluminum chlorohydrate.

How does it work against odors?

Unlike conventional deodorants that mask odors, alum stone acts at the source. Its aluminum ions create an environment hostile to the bacteria responsible for bad odors (mainly Staphylococcus hominis and Corynebacterium). No bacteria, no odors.

It is not an antiperspirant: it does not block perspiration, which is a natural and essential thermoregulation mechanism.

Reference: Callewaert C. et al. (2014). "Deodorants and antiperspirants affect the axillary bacterial community." Archives of Dermatological Research, 306(8), 701-710.

Is it safe? The lowdown on aluminum

The question of aluminum often comes up. It is important to distinguish between two forms:

Aluminum salts in conventional antiperspirants (aluminum chlorohydrate): soluble, penetrate the skin, subject to scientific debate.
Potassium alum in alum stone: large molecule, very poorly absorbed by healthy skin. Available studies do not show a significant risk with normal topical use.

Reference: Namer M. et al. (2008). "The use of deodorants/antiperspirants does not constitute a risk of breast cancer." Bulletin du Cancer, 95(9), 871-880.

Its other benefits

Astringent: tightens pores and soothes irritation after shaving
Hemostatic: stops minor bleeding (razor cuts)
Mild antifungal: useful for feet
Ecological: zero plastic packaging, lasts 1 to 2 years
Economical: a single purchase for a long period

How to use it?

Moisten the stone and apply it directly to the skin. It is odorless and does not stain clothes.

Here are the main applications of alum stone (potassium alum):

1. Main use: Natural Deodorant

The best known and most used.
Neutralizes odor-causing bacteria without blocking perspiration.
Effective for 24 hours, fragrance-free, suitable for sensitive skin.

2. Aftershave / Shaving care

Hemostatic: quickly stops minor bleeding (razor cuts).
Soothes razor burn, reduces redness and irritation.
Tightens pores and limits ingrown hairs.

3. Skin care

Astringent: tightens pores (useful for oily or acne-prone skin).
Soothes irritations, minor wounds, and insect bites.
Can be used as a facial tonic (diluted).

4. Foot care

Foot bath: soothes tired feet, reduces odors, and has a mild antifungal action.
Sprinkle alum powder in shoes to absorb moisture.

5. Other common uses

Cold sores: local application (lightly touching with the wet stone).
After epilation: calms the skin and reduces the risk of irritation.
Hair care: in a diluted rinse to reduce excess sebum on the scalp.
For the whole family: very gentle, can be used on children (except on broken skin).

Usage tips:

Lightly moisten the stone with clean water before applying to damp skin.
Allow to dry naturally on the skin.
A good sized stone usually lasts 1 to 2 years.

Natural vs. Synthetic Alum Stone

Beware of fakes! Real natural alum stone is composed of potassium alum. Some cheap products contain ammonium alum (synthetic), which is less recommendable. Always check the composition.