Specialty & fine chemicals
Antiperspirants without aluminium
How aluminium salts form a transient plug in the eccrine duct, why aluminium-free products act on odour rather than on flow, and the pH problem with the first-generation bicarbonate alternatives.
“Aluminium-free antiperspirant” is close to a contradiction, and understanding why is the fastest route into what these products do.
What an aluminium salt does
Antiperspirant actives are aluminium chlorohydrate and the aluminium–zirconium complexes. Applied to skin, the salt encounters near-neutral, dilute conditions in the eccrine duct and the polymeric aluminium species hydrolyse and precipitate as an amorphous aluminium hydroxide gel, forming a plug in the upper duct. Interaction with duct keratin and with mucopolysaccharides in the sweat contributes to the plug’s stability.
Three properties of that plug matter. It is superficial — in the duct’s upper portion, within the stratum corneum. It is physical, not pharmacological: no gland is inhibited and no nerve is blocked; the fluid is simply obstructed. And it is transient, cleared over days as the surrounding corneocytes desquamate, which is why the product has to be reapplied.
Efficacy is measured gravimetrically — sweat collected over a fixed period in a controlled hot room, before and after treatment — so this category has an unusually objective endpoint, and any product claiming to reduce sweating can in principle be held to it.
Why removing the aluminium changes the category
No non-aluminium cosmetic active is established as forming an equivalent duct plug. A product with no aluminium salt therefore does not reduce sweat volume, and its claims move to the second half of the problem: the bacterial conversion of odourless apocrine precursors into volatile acids and thiols. That is deodorancy, and its mechanisms are covered separately under enzyme and probiotic deodorants — competition, acidification, or interference with the releasing enzymes.
The consequence for a buyer is concrete. Wetness and odour are different endpoints with different tests. A gravimetric reduction claim and an odour-panel claim are not interchangeable, and a “natural antiperspirant” that reports only the latter has not made the former.
The bicarbonate problem
The first generation of aluminium-free products leaned on sodium bicarbonate, which works: it neutralises the short-chain volatile fatty acids that carry much of the odour, and it raises local pH beyond the range in which the odour-forming corynebacteria grow well.
The same property is the problem. A bicarbonate suspension sits well above neutral, against a skin surface maintained at pH 4.5–5.5. That gradient, applied daily to occluded, frequently shaved skin, is a plausible cause of the irritation reported by a substantial fraction of users — and it is why current formulations market themselves explicitly as bicarbonate-free, having substituted magnesium hydroxide, which is less alkaline in suspension, or moved to ferment-based actives that work with the acid mantle rather than against it.
Blocking sweat has been the subject of long-running debate about aluminium absorption; the regulatory assessments have not established a systemic hazard at cosmetic exposure levels, and the honest statement is that the category’s shift is driven at least as much by consumer preference as by a demonstrated safety finding.