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I have a fantasy race that controls fire, and loses their powers when they get wet.

They bathe by scarping all dirt and materials off their skin and heating the outside of their body to 600 degrees Celsius (1,112 degrees Fahrenheit) with no ill effect. For the question, you can assume the creatures sweat like normal humans, but when are exposed to extreme heat they magic it away (as any smells produced by the heat removal process are outside the scope of this question)

Assuming they are otherwise human in terms of diet and physiology, would this heat eliminate normal human body odor, and are there any smells that soap and water would remove that this method does not?

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    $\begingroup$ Do you realize that human skin and sweat glands can't even closely tolerate 600 C? Do you want to handwave this detail? $\endgroup$
    – Alexander
    Feb 10, 2020 at 21:07
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    $\begingroup$ This question can't be answered with the information provided. Your race might be able to get rid of the odors associated with whatever they've been rolling around in or whatever, but there's still going to be odors associated with whatever mechanisms your race uses to regulate all that heat, and if we don't know how that's done, we can't answer the question. $\endgroup$ Feb 10, 2020 at 21:12
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    $\begingroup$ @at_ well, the ASH would smell like ash, but if they scrape the ash off, then they smell like whatever their skin smells like when it's heated to 600C, but we don't know what that is. It's not the same stuff HUMAN skin is made of unless it's Just Magic, in which case it could smell like anything. $\endgroup$ Feb 10, 2020 at 21:17
  • $\begingroup$ @Morristhecat: Point taken, but if it could smell like anything, than the question would be obsolete, wouldn't it? :-) $\endgroup$
    – at_
    Feb 10, 2020 at 21:20
  • $\begingroup$ I edited the question to make it more clear, attempting to limit the scope of the question to make it more answerable. $\endgroup$
    – Hink
    Feb 10, 2020 at 21:28

3 Answers 3

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Your creatures will smell like burnt stuff.

Merely trying to remove stuff from your skin mechanically will not do, there will always be some leftover. It is also not practical to remove sweat.

Speaking of which, sweat isn't just pure water (otherwise it wouldn't smell!). It's water plus bodily wastes and some more things. The wiki lists:

  • Lactic acid
  • Urea
  • Many different minerals

And then it says:

Some exogenous organic compounds make their way into sweat as exemplified by an unidentified odiferous "maple syrup" scented compound in several of the species in the mushroom genus Lactarius.

Don't forget it's loaded with bacteria, which will produce their own stuff.

Why does it matter? Because while water will simply evaporate over 100 degrees C, other components will break down into other stuff - urea will break into cyanuric acid, ammonium chloride and ammonia, so during a fire bath a creature will be very hard to approach even for other creatures resistant to fire.

After the bath, the minerals will still be there, dried up. A lot of salt will remain, for example. It's melting point is at 801 Celsius. So you have very hot salt, which will trap a lot of material from the bacteria, might give you a burning smell.

Then there is also some sugar in sweat. It will break down into carbon chains. Whatever doesn't evaporate will recompose as some either brownish or black tar. That's the kind of thing that makes unwashed teflon pans sticky. Consider the effect of this for your burning creature.

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    $\begingroup$ keep in mind that a lot of body odor is the bacteria that grow in old sweat, if you keep incinerating them and the sweat, they will not get a chance to grow. so at least no BO. $\endgroup$
    – John
    Feb 10, 2020 at 22:11
  • $\begingroup$ @John ovens also go over 100C usually and there are bacteria in them too. There are no bacteria while they are hot. It's the cool periods that are problematic. $\endgroup$ Feb 10, 2020 at 23:32
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    $\begingroup$ The cleaning will be just as frequent as bathing and more thorough to boot. And the bacteria in question need stale sweat to grow in. It will be just as effective at combating BO as bathing if not more so, since you are drying instead of moistening. . $\endgroup$
    – John
    Feb 11, 2020 at 1:27
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Heating their body would only burn/dry/oxidize anything on their skin, not take it away. They would probably do better taking baths in sand, which could remove dirt, dead skin, and oils without needing water. This is called dust bathing and is practiced quite a bit in nature. If there were anything that dust bathing couldn't remove, like something sticky we'd normally wash off, the fire would come in handy. It could convert the sticky substance to ash which could easily be washed off in the sand.

In addition, they might perfume themselves with incense, rather than oils, since it's already designed to smell good when burning.

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They will not smell.

Any carbon or nitrogen containing compounds (oils, fatty acids, desquamated skin) will either volatilize and escape as vapor, or be oxidized to CO2 and H2O.

What will remain is salts. Sodium and potassium chloride are the main ones and those will not volatilize at these temperatures and will remain on the skin. Those salts are odorless. If they are sweaty to start with, these people might have a dusty white residue on their skin, which is salt.

They might be accompanied by licky dogs, who will help clear off the residue after the people cool down.

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