Sweating Soap: Causes, Prevention, & Fixing it
What is soap sweating?
If you don’t know what I’m referring to about soap sweating, then consider yourself a lucky soapmaker so far! The rest of you know what I’m talking about! You’ve just made some lovely melt and pour soap. After it’s hardened, you pop your beautiful soap bars out of their molds and then the next day you see it. It looks like frost or fuzz at first, upon closer inspection you see hundreds of tiny little water droplets covering the surface of your soap. There’s another name for this phenomenon, it’s also called glycerin dew (that sounds nicer, hmm?)
What causes soap to sweat?
Melt and Pour soap base contains glycerin, an organic compound also known as glycerol. It’s a clear, odorless liquid at room temperature and is derived from animal fat and vegetable oil. It’s also a natural byproduct of the saponification process. Glycerin is a humectant / hygroscopic. That means it absorbs and attracts ambient water. If you left a cup of glycerin out in a humid room, it would actually absorb water from the air until it was about 20% water. In soap, glycerin helps moisturize your skin and seal in moisture. Glycerin is a key ingredient for making clear soaps. Okay so what is the point here?
The glycerin content in your soap actually causes your soap to become hygroscopic and so if your soap has a high level of glycerin in it and you let it sit out in a humid environment, the soap will collect water from the room and little droplets of glycerin dew will cover your soap. Humidity is the number 1 cause of glycerin dew on your melt and pour soap.
How can soap sweating be prevented in M&P?
The best way to prevent your soap from sweating is to wrap it in plastic wrap or shrink wrap once you remove the soap from the mold. You can also store your soap in airtight containers to help to prevent sweat on your soap. In the airtight container you could add silica packets or uncooked rice in a satchel to help absorb any humidity in the container so it stays off your soap! Reducing humidity is the key to preventing soap sweat
Another very helpful tip is to start with the right soap base. Some soap bases are much less susceptible to glycerin dew. Look for low sweat or an ‘LCP’ (like cold process) base. I find that bases by the manufacturer SFIC tend to sweat much less than others. Also certain types of bases (like clear/transparent ones) sweat more. Click here for Low Sweat soap base (“LCP” sold at Brambleberry, manufactured by SFIC)
If you don’t wrap or seal up your unmolded soap, store it in a cool dry environment. Keep a dehumidifyer in your soaping area. Keep the room temperature constant as you make your soap, let it harden, remove from the mold, and store because changes in temperature can affect humidity. Let your soap cool slowly and naturally rather than putting the soap in the freezer to unmold. When you pull the soap out of the freezer the cool temperature will attract water in the air just as an ice cold beverage glass does.
How does sweat on soap affect it’s properties?
Soap Sweat / Glycerin dew doesn’t affect your soap’s ability to clean. It just happens when your soap is in a humid environment – it’s doing the job it’s intended – attracting moisture! The only real effect is the appearance of your soap. Hopefully you can prevent glycerin dew with the strategies listed above but, soap sweat may still show up.
How to fix or remove glycerin dew
If you found this article because this has already happened to your soap, you are probably looking for a solution to soap sweating. To get rid of soap sweat, you could try remelting your soap in the microwave or double boiler (be sure not to over heat), and pour it back into molds again. This time around, make sure to keep soap in a dry environment. Otherwise you would just let your soap dry out a bit, but it will have a texture on the surface left over from the glycerin dew.
Do you have any other tips or a related story? Comment below and share!
I put all the melt and pour soap I have made in individual, sealed plastic bags, and some are still developing soap sweat. Does plastic wrap work better?
That happens to me too sometimes. The best option is keeping the soap stored in a dry environment if possible. I think either way – bags or wrap – would be equivalent
How I control soap sweating problem permanently.
Suppose we are taking all the precautions to not coming moisture on soap but after the soap get sold out and in customer bathroom it leaves moisture how would i control it permanently
I’m really not sure except switching soapmaking method to cold or hot process or switching to a syndet bar
I mist with alcohol too, and that seems to clear it up. I only experience it if we have several days of rain.
Thanks, will try that immediately.
Hi, your article was very informative and helpful. Thank you. I have one question. About how long should you keep the m&p soap wrapped in saran/plastic wrap before unwrapping? Thank you!
until ready to use
I used 76% alcohol in a rum bottle for my glycerine soap as I live in Canada and that was pretty much the highest alcohol content I could find. I did everything to the book and the glycerine soap is not hard after 48 hours? What can I do to correct the situation. Reheat it?
It should definitely be hard after 48 hours. do you recall how much alcohol you used? I recently made a batch of MP soap – SFIC base and lightly spritzed with 70% isopropyl alcohol after pouring into the mold just to pop the bubbles. and it hardened up within a few hours.
I was, when i put my curing cabinet in a new room, all of my soap get sweating (glycerine dew) when rainy day… maybe its because the weather of environtmen… so i need change my curing cabinet location again…
Soap sweat or dew is caused by the glycerin and other water attracting compounds in the soap that concentrate water from the air onto the soap surface. The water beads up because of the waxy or water repelling components of soap. This condition happens when the soap is drying the air instead of the soap drying in the air. A light misty spray of 91% rubbing alcohol and a quick fanning of a blow dryer will correct the problem. Make sure the rubbing alcohol is 91% or better and not 70%.
Awesome tip, thanks! 🙂 So this tip will help remove/dry up the soap sweat if it’s already happened! Great addition to this article because many people find this article *after* they already experienced this problem
I made a few different soaps, the one that I made that had 1/4 cup of coffee in it has been the only one that hasn’t sweat. Maybe from adding the moisture to the soap has stopped it from sucking the moisture from the air in? Anyway, I do have a question. I have wiped my soaps can I wrap them in Saran wrap if they still feel wet or will they mold?
Hmm I try not to add any liquids or wet ingredients to my M&P soaps.
I would ensure soap bars are nice and dry before wrapping them, otherwise you’re just trapping the wetness inside and it gets sticky and kinda looks gross. I haven’t experienced MP bars molding before, but I only wrap mine when they are dry
this was incredibly helpful, as I just used a SFIC glycerin base and was wondering if I could remelt it (even though it has some rose petals in it. I’m going to go for it. Thanks again!
Is there a bad effect in cold processed soaps? Shall I wipe off the sweat of the soaps?
I’ve only experiences soap sweating in Cold Process soap when I did a brine soap (dissolve sea salt in water before adding lye). Otherwise I don’t really get sweating on my CP soaps
Does sugar solution also causes sweating if yes what causes more sugar solution or glycerin
I am not totally sure. Would be a good experiment to see if 2 soaps of the same recipe sweat differently if 1 has sugar and the other doesn’t. Keep an eye on the blog, it may be a future post and addition to this article!
I have used sugar in MP recipes and those soaps did sweat, but I cannot say for certain that it was due to the sugar. Because glycerin dew is just a simple fact of Melt and Pour soapmaking! Best bet is to do your best to prevent it by using a low sweat base and then wrapping bars in plastic or storing in an air-tight container right away.
Thanks for reading!