Aluminum Sesquichlorohydrate

Aluminum Sesquichlorohydrate is an aluminium salt used as the active ingredient in antiperspirants. It belongs to a family of related compounds that includes aluminium chlorohydrate and the aluminium zirconium complexes found in many stick and roll-on products, and the sesquichlorohydrate version sits at a particular ratio of aluminium to chloride within that group.

The distinction between an antiperspirant and a deodorant is worth making, because the two words are often used interchangeably. A deodorant addresses odour, generally by tackling the bacteria that produce it or by masking it with fragrance. An antiperspirant reduces the amount of sweat reaching the surface, and aluminium salts are what make that happen. Many products do both.

On an ingredients list it appears as Aluminum Sesquichlorohydrate, usually at or near the top, and typically at figures in the region of 10% to 25%. Antiperspirant actives are regulated, and the permitted levels and labelling requirements are defined rather than left to the manufacturer.

You will find it in roll-ons, sprays, sticks and creams for underarm use. It is generally well tolerated, though the underarm is a sensitive area and irritation is not unheard of, particularly on skin that has just been shaved.

Concerns linking aluminium in antiperspirants to serious illness have circulated widely for years. Regulatory bodies that have reviewed the evidence have not found it supports those claims, and the ingredient remains permitted for cosmetic use. If it worries you, aluminium-free deodorants are widely available, though they address odour rather than sweat.

Aluminium salts work by forming a temporary plug. When the product is applied, the salt dissolves in the moisture on the skin and reacts to form a gel-like precipitate that settles into the openings of the sweat ducts. That plug physically restricts the flow of sweat to the surface. It does not stop the body sweating, and it does not affect sweat glands elsewhere; it blocks the exit route in the area where it is applied.

The plugs are shallow and temporary. They are gradually worn away by washing and by the natural turnover of skin cells at the surface, which is why antiperspirants need reapplying and why the effect builds over several consecutive days of use rather than being at its strongest on the first application.

Because odour is largely produced by bacteria acting on sweat rather than by sweat itself, reducing the amount of sweat also reduces odour indirectly. Many formulations add a deodorant component as well, which is why a single product often does both jobs.

Irritation, when it happens, generally comes from the acidity of the salt in solution combined with a warm, occluded area of thin skin. Applying to freshly shaved or broken skin makes it considerably more likely.

Antiperspirants work better with a little technique than most people expect.

• Apply at night, to clean, completely dry skin. Sweat production is lower overnight, which gives the plugs time to form properly. This single change makes the biggest difference to how well it works.
• Dry skin thoroughly first. Applying to damp skin dilutes the product and increases the chance of stinging.
• Do not apply straight after shaving. Leave it several hours, or apply the night before you shave rather than the morning after.
• Expect it to build. Several consecutive nights of use works better than a single heavy application.
• You can still shower in the morning. The plugs form overnight and are not simply washed away.
• If it stings or the skin reddens, switch to a lower-strength product or an aluminium-free deodorant.
• It can mark clothing. Letting it dry fully before dressing reduces this.
• Underarm use only. These products are formulated for that area and are not intended for the face.

If excessive sweating is affecting your daily life, that is worth discussing with a healthcare professional, as there are options beyond over-the-counter products.