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We all use deodorant and they always feel cold, why is that?

Is it because it is liquid inside the bottle and a gas when it is released?

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@Qmechanic: the first link isn't relevant since it's mainly the vaporisation that cools the spray rather than the expansion. The second link is valid for deodorants where ethanol will evaporate off the skin. –  John Rennie Sep 26 '13 at 18:38

2 Answers 2

up vote 6 down vote accepted

Yes, the deodorant contains a mixture of low boiling point alkanes, such as butane, that form a liquid under pressure but evaporate when the pressure falls to one atmosphere as they leave the can. It's primarily the latent heat of vaporisation that reduces the temperature and makes it feel cold.

In addition to this, deodorants (as opposed to antiperspirants) contain ethanol - they are essentially just a solution of perfume in ethanol plus propellant. The ethanol evaporates on the skin and again the latent heat of vaporisation cools the skin.

In a can of deodorant the dip tube goes down into the liquid propellant. When you press the button the pressure in the can forces liquid alkane up the dip tube and out. The alkane mostly evaporates in the tube and nozzle, but if you hold the can very close to your skin you can get liquid alkane on the skin. This evaporates very rapidly, and it's really cold!

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Hmmm. I would have put it down to adiabatic expansion, but this definitely should also play a role. And you probably know better. –  Emilio Pisanty Sep 26 '13 at 18:41
@EmilioPisanty: the pressure inside an aerosol can is only 3-5 atmospheres so the gas doesn't expand/cool that much when released. –  John Rennie Sep 26 '13 at 18:52
Yeah, I guess. You can get the can pretty cold, though, by completely emptying it after the deodorant is finished. (But then again, that's an expansion by a factor of ~3 instead of a few percent.) –  Emilio Pisanty Sep 26 '13 at 18:54
Are all Lynx employees as well-versed in physics as you? –  joshphysics Sep 26 '13 at 18:55
Grin :-) Lynx is made (in the UK) by Elisa Fabergé, which is owned by Unilever. I worked as a colloid scientist in Unilever's central research lab. All physical chemists are secretly paranoid that they're not real scientists, so as soon as I quit and had the spare time I started learning GR! –  John Rennie Sep 26 '13 at 19:03

I think that might not be the reason related to physics the actual reason is the perfume bottle consists of compressed gas that means which is unstable at normal temperature and hence when the liquid is sprayed on the skin it quickly absorbs the temperature of the body and evaporates hence we feel cold at that instance due to loss of heat from our body

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And how is the evaporation is not related to physics? –  Ignacio Vergara Kausel Oct 25 '13 at 11:20

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