Nick, South Africa asked:
Do antiperspirants, used in the armpits, make you sweat more elsewhere on your body?
Chris - The way that antiperspirant deodorants work, most of them are spray-ons, some roll-ons, they tend to contain lots of zirconium, aluminium zirconium salts and pro-hydrate salts. The way they work is that you rub them on your skin and they form a layer on the surface of the skin, and wherever they come into contact with water from your own body, in other words, where there's a pore linked to a sweat gland under the skin, they soak up the water and then they form a little plug of gel-like substance inside the sweat gland, stopping any more water coming out.
If you, therefore, stop the water coming the skin surface becomes drier. And the reason that we want to make the skin surface drier is that if you have dead skin and water together in a warm wet place, you've got the perfect bacterial banquet. Itís this bacteria eating your dead skin, flourishing and thriving in this warm damp environment that makes the whiff that we want to avoid. So, we tend to apply the deodorants where we sweat the most and you tend to sweat in those places for various reasons. One of them can be thermal. You do sweat to cool down because when you sweat, you put a thin layer of water on the skin surface. The water is exploiting an effect called the latent heat of vaporisation. In order for the water to go from a liquid into a gas, it has to rob extra energy from the skin surface to break the molecules apart. They're all sticking together as a liquid and to separate out as a gas it needs extra energy to do that and so, when you've got the water on the skin surface, itís taking the extra energy away and that cools you down very efficiently, and that's why we sweat.
But sweating is also under the control of something called the sympathetic nervous system and that means that itís under the control of a part of your nervous system that you activate when you're worried about things. So people can also break into a sweat when they're very, very panicky, panic stricken, anticipating having to run away very fast, and things like that. As a result of that, you can also sweat everywhere on your body for a variety of non-thermal reasons. So, just putting on antiperspirant deodorant won't necessarily affect the rate of sweating on other bits of the body because if you're doing a stressful job, you might just sweat elsewhere.
Dave - But I guess if you're sweating for thermal reasons then you're going to have less skin to lose the heat from so the rest of you is going to be slightly hotter so you might sweat a bit more of the rest?
Chris - I take your point, but I would say, the skin area that you're applying antiperspirant to is such a tiny fraction compared with the whole of the rest of your body that it probably is going to make almost zero difference.