I was just in my AP Chemistry class earlier today learning about hydrates and their properties. It occurred to me that a compound with so much water could aid in moisturizing the skin. Is this a valid thought? And if so, could hydrates be irritating to the skin?

Through research, I personally thought Natron may be an option in a solution added to a cream or lotion.

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    $\begingroup$ Hydrates have a high affinity for their water, and probably will not give it up for your skin. Some may even draw water out of the skin. $\endgroup$
    – user137
    Aug 27, 2014 at 21:37
  • $\begingroup$ @user137 I think that is the correct answer, if you'd care to expand on it a bit. $\endgroup$
    – jonsca
    Aug 28, 2014 at 12:00

2 Answers 2


I do not think that hydrates will serve as good moisturizing agents, because they usually do not loose their crystal water unless when being heated. Magnesium sulfate heptahydrate, for example, starts to loose water at temperatures above 50 °C, and complete dehydration of the salt is only achieved at temperatures above 310 °C. Some hydrates can even have a dehydrating effect when they react with moisture to hydrates with higher $\ce{H2O}$ content. Calcium sulfate hemihydrate, for example, reacts with water to form the dihydrate in an exothermic reaction. The stability of hydrates is the reason why many anhydrous salts which are easily hydrated are used as drying agents, for example, sodium sulfate and magnesium sulfate.


This isn't necessarily true (that hydrates will hydrate your skin). For example, $\ce{MgSO4*7H2O}$ is Epsom salt. Do salts sound particularly hydrating? No.

Furthermore, dehydrated hydrates have a high attraction for water, as seen in $\ce{CaSO4}$. When hydrated, it forms plaster of Paris, which can be dried to make drywall.


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