Low-impact living: Once upon a time, locker-rooms smelled of sweat, old socks and other human pungencies. I don't miss these odours, but I don't care for those that have replaced them. Nowadays we have the "phsshhhhh" of people's poorly aimed aerosols filling the room with their preferred brands of antiperspirants. It's not just the pong of the perfumes that permeates the air: part of the haze consists of microscopic droplets of propellants.
These hydrocarbons are volatile organic compounds, chemical sneezes that pollute the indoor atmosphere. A 2004 Bristol University study showed that daily use of aerosols was associated with increased instances of infant diarrhoea and adult headache. Roll-on or stick applicators deliver the stuff where it's needed and use less superfluous chemicals, so they're more economical, kinder to the environment and less annoying to the people sharing the same space when they are applied.
The active ingredient in all antiperspirants is aluminium, in the form of one of several compounds. It causes the sweat duct to become temporarily plugged, thus preventing the passage of moisture to the skin's surface.
Aluminium has been associated with Alzheimer's disease, but the link has not been conclusively proven. Those who want to limit their chemical exposure might consider a deodorant rather than an antiperspirant. Sweat in itself is odourless. The whiff arises when bacteria that live in the warm and humid armpit start to breed (I'm sorry, but think of it as science rather than something personal). Deodorants don't contain aluminium, usually forgo artificial fragrances and parabens (possibly harmful preservatives) and are generally obtainable only as "natural" products in organic and health-food shops. Their active ingredients inhibit bacterial growth. You will still sweat, but you won't smell feral - at least for a few hours.
An ancient body-odour suppressant, around for thousands of years and still regularly used in Asia and South America, is the naturally occurring ammonium alum, known as crystal deodorant or deodorant stone. Several brands are available. Wet the stone, apply liberally, and the bacteria will be battened down for several hours. Finally, another entirely natural substance for taming the underarm area is our old friend bread soda. Mix four parts bread soda with one part cornflour and whoosh it on with an old blusher brush. Bread soda is also recommended for removing stains from clothing - including those from antiperspirants.