Antiperspirants are deodorants that as well as masking body odour, also slow the rate of sweat excretion. Today, antiperspirants are typically sold in a rollerball applicator and are solid substances comprising several ingredients, including an aluminium-based compound, wax, liquid emollients and natural scent enhancers. The key to the sweat-blocking power, however, rests purely in the active aluminium- based compound that, in a typical commercial antiperspirant, makes up 10-25 per cent of the ingredients.
Ions of this compound – examples of which include aluminium chlorohydrate and aluminium chloride – are withdrawn into the cells that line the human body’s eccrine gland ducts. The eccrine glands are responsible for producing the majority of the body’s sweat and are located en masse in the armpits. As the compound’s ions are absorbed into the ducts, they carry water with them, causing the ducts to bulge and swell to a level which forces them shut. As a consequence of this process, any sweat is directly blocked from being excreted through the skin as it normally would.
Once the eccrine ducts have been closed, the other odour-reducing/masking ingredients provide a thin coating to the skin’s top layer. The gland ducts will remain closed until the water content both outside and inside the gland cells reaches equilibrium – the cells can only absorb a ﬁxed quantity of water – and the cell content begins to pass back out through osmosis. Typically antiperspirants are designed to last for a period of hours, before a top-up is needed.