# 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. An antiperspirant plugs a duct; a deodorant changes a chemistry. Dropping the aluminium salt does not make a gentler antiperspirant — it changes which of the two things the product is. Source: https://en.bioecon.ru/docs/biochem-industrial/specialty-fine-chem/bio-antiperspirants/ Updated: 2026-08-25 "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](../enzyme-based-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.