I’m pretty excited to share this Satsuma Shower Gel with you guys—mostly for two reasons. Reason #1: I was utterly obsessed with The Body Shop’s “satsuma” line as a kid, and I’ve had this gorgeous satsuma dupe fragrance oil for years, meaning to make satsuma-y things with it—and I finally am! Reason #2: this is the first self-preserving hydrous formulation I’ve shared. It’s been a long time in the making/testing, and I’m excited to finally share it.
Want to watch this project instead of reading it?
It was inspired by LUSH’s self-preserving liquid shower gels. They combine quite a lot of glycerine with anionic Sodium Laureth Sulfate (SLeS), amphoteric Sodium Cocoamphoacetate, lactic acid for pH adjusting, and carrageenan to thicken. Each gel also contains a selection of essential oils, infusions, extracts, and colourants to differentiate them from one another. There are no preservatives—so how do they stay fresh?
I’ve been doing lots of reading and research into preservatives, spoilage, and hurdle technology over the last few years, and from my research, I believe there are several factors at play here. One of the best articles I’ve read on self-preserving/preservative-free products/hurdle technology is this two-piece (part 1 + part 2 + the extensive references at the bottom for even more info) one from Botanical Formulations—it does a great job of discussing the different tactics a formulator can combine to create a formulation that keeps itself in check. Definitely give it a read!
Tactic #1 with this formulation: reducing the water activity with a high concentration of glycerin (30%). Just because water is present in a formulation doesn’t mean it’s available to any microbes looking for a watery home—humectants like glycerin, propylene glycol, sugar, and salt can, in high enough concentrations, “lock up” the water in a formulation, effectively keeping it too busy to get into any trouble. Think about honey—it does contain water, but it also contains so much sugar that that water activity is too low for anything to grow. If the honey is diluted with water the water activity will gradually increase to a point where the honey/water solution can spoil, but pure honey is incredibly shelf-stable. Be sure to give this a read to learn more.
Tactic #2 is pH; I’ve kept the pH of this formulation around 4–4.5. “Most microbes, and especially pathogenic ones, can survive and grow in a pH of between 5 and 8, so slightly acidic, neutral and slightly basic. Most bacteria prefer a neutral pH of between 6.5-7.5 and most gram positive and gram negative bacteria cannot survive below pH 4.5. However many pathogenic yeast and moulds can thrive in acidic pH levels below pH 4.5” (source). That acidic environment isn’t inhospitable to everything, but it does reduce the variety of things that could set up shop in our shower gel. The LUSH product contains some lactic acid to lower the pH; I used citric acid as that’s what I have. I worked to incorporate the citric acid directly into the formulation so you don’t have to do a ton of testing and adjusting (as I’ve done it for you!) but I do recommend checking the pH of the final product just to be certain it’s where we want it to be.
Tactic #3 is good manufacturing practice. I always take care to create in a clean environment, with clean equipment, but I was extra careful here, misting things with 70% isopropyl alcohol and letting it evaporate off before carrying on. The less contamination from the get-go = the less likely the product is to spoil as time goes on.
Tactic #4: A general lack of anything particularly delicious to microbes. There’s nothing super interesting in this shower gel—no powdered botanicals, no oils, no proteins, no clays, etc. After the water and glycerin, we have a wee bit of carrageenan, citric acid, and fragrance. The rest of the formulation is comprised of anionic and amphoteric surfactants.
Tactic #5: The packaging doesn’t allow the user to stick fingers into the product, and the orifice is small, reducing the chances of anything getting into the end product and contaminating it.
Ok! So that’s the theory—does real-world performance confirm this multi-point hypothesis? I made two batches of this shower gel in early September 2019 and stored them in my shower for months, using them and keeping an eye on ’em for any signs of spoilage. After eight months, there was nothing—no change in consistency, no clouding, no change in scent, nothing. Without a proper test, it’s hard to confidently say they’re still fine at the 8-month mark, but given how rapidly microbes reproduce when left un-checked, I think it is safe to say this body wash is shelf-stable for at least four months. You certainly don’t have to leave this self-preserving if you don’t feel comfortable—it would be very easy to reduce the water by 0.5% and include 0.5% Liquid Germall Plus (INCI: Propylene Glycol, Diazolidinyl Urea, Iodopropynyl Butylcarbamate)—but this has been an enjoyable formulation challenge for me. I hope you enjoy it as much as I have!
Want to watch this project instead of reading it?
Satsuma Shower Gel
For the water and dye: weigh the distilled water and dye into a beaker or glass measuring cup. You are unlikely to be able to weigh out the dye due to the very small amount; what I did was weigh about half the water into the measuring cup, and then dip a clean spoon or glass stirring rod into the bag of dye so there was just a tiny amount on it, and then swished that spoon around in the weighed-out water before topping it off to a full 28.7% distilled water. If you were making a 5kg batch of this you’ll likely be able to weigh out the dye properly, but the dip-and-swish method works well for a 150g batch (and that’s a decent amount of shower gel). Add the citric acid to the coloured water, and stir to combine.
Combine the water and surfactant mixtures. Stir gently to combine, cover, and leave to thicken and dissolve for an hour or so (overnight is also very convenient!). Once the mixture has thickened and is uniform (you’ll need to give it another stir after it sits to ensure everything is well mixed) we can move on to checking the pH of the body wash.
Weigh 2g product and 18g distilled water into a small bowl or beaker and whisk to combine (wondering why?). Check the pH with your pH meter (I have this one [USA / Canada]). Depending on the shape of your bowl/beaker you may need to tilt it in order to fully submerge the sensor on your pH meter. If your ingredients are all pretty similar to mine, it should fall between 4.1–4.4, and that’s great! If the pH is above 4.5 or lower than 4, you’ll need to adjust it. Please read this article if that’s the case.
Once we’re sure the shower gel has the proper pH all that’s left to do is transfering it to our packaging. I used a 120mL (4 fl oz) tottle. Use as you would any shower gel. Enjoy!
In my testing, this self-preserving shower gel showed no changes after 8 months. To be on the safe side, I would recommend using it within four months. If you add a preservative it should easily remain stable for at least 1–2 years.
As always, be aware that making substitutions will change the final product. Given the self-preserving nature of this formulation, I don’t advise making any changes to this formulation unless you want to either add a preservative or re-test the formulation for stability over the course of several months. Keep this note in mind as you read the following list:
- As I’ve provided this recipe in percentages as well as grams you can easily calculate it to any size using a simple spreadsheet as I’ve explained in this post. As written in grams this recipe will make 150g.
- To learn more about the ingredients used in this recipe, including why they’re included and what you can substitute them with, please visit the Humblebee & Me Encyclopedia. It doesn’t have everything in it yet, but there’s lots of good information there! If I have not given a specific substitution suggestion in this list please look up the ingredient in the encyclopedia before asking.
- You could try propanediol 1,3 or propylene glycol instead of the glycerine
- You could try a different thickener (xanthan gum, guar gum, etc.) instead of the carrageenan
- You could adjust the amount of carrageenan to get a thicker or thinner end product
- The dye is optional; you can replace it with more water if you don’t want to use it (I expect this change could be made to the self-preserving version without any need to re-test)
- If you’d like to learn more about the surfactants used and compare them to ones you might already have so you can make substitutions, check out this page. Sodium Coco Sulfate (SCS) would probably be my first choice, but it is significantly more concentrated than Sodium Laureth Sulfate (SLeS), so you must adjust the formulation to have a similar final active surfactant matter.
- Satsuma is a citrussy scent; if you don’t have it I’d look at other citrussy fragrance oils or essential oils.
The orange water-soluble dye was gifted by YellowBee.