Wednesday, May 15, 2013

Troubleshooting a lotion recipe...

In this post on making a basic lotion, Courty asks: I tried your summer lotion the other day. (Was it this one?) I love it but have a problem I was hoping you could help with. It rubs in very well when my skin is dry but if I apply it after I get out of the shower it drags and skips and doesn't rub in smoothly at all! Do you know why this happens and if I can fix it? I used what I had so I simplified a lot when substituting your recipe.

Here's my formula:
71% Water
3% Vegetable Glycerin
20% Organic Olive Oil
3.6% Glyceryl Stearate
1.4% Cetyl Alcohol
.5% Potassium Sorbate
.5% Vit E

Quick aside: Please always include your process when writing to ask me for help. It makes it so much easier to figure out what you did.

It sounds like the emulsion is breaking when you apply it to your skin. I think the problem is that your lotion isn't properly emulsified. You aren't using an all-in-one or combination emulsifier and you don't have a complete HLB emulsifier. Glyceryl stearate is a low HLB emulsifier (HLB 3.8) that needs to be paired with a high HLB emulsifier to create a complete emulsifier. Cetyl alcohol isn't an emulsifier - it's an emollient like our oils and butters - so you have an incomplete emulsifier in the form of glyceryl stearate. You could include any of the higher HLB emulsifiers to make this work, but you'll need to work on the math again!

So why is this happening only after a shower? It could be you're adding just enough water to mess with the product or it could be coincidence. Either way, the lotion is unstable and the emulsion will break sooner rather than later.

Why has it remained stable for a while? Emulsification relies upon three things - heat, mixing, and chemistry. The chemistry part is the all-in-one emulsifier. The heat is the heating and holding part. And the mixing is the mixing part of the process. You can get an emulsification using only one of these three things - look at shaking a salad dressing - but it will fail in a really short period of time, like hours. You can get an emulsification using heat and mixing - look at using beeswax (not an emulsifier) in a lotion - but again, it will fail. Using all three ensures we get a nice, stable emulsion that won't fail for a while. (All emulsions will fail eventually, but when we use all three methods, we could see it last for years, well beyond the time it is good!)

Related posts:
Emulsifiers: Questions about VE and MF emulsifiers
Emulsifiers: Check what you've got! 
HLB system (PDF from Lotioncrafter)
When lotions go wrong! 

As a secondary note, you aren't using a broad spectrum or complete preservative in this product. Vitamin E is an anti-oxidant, not a preservative, which is to say that it helps retard the rancidity of our oils, butters, and other ingredients with fatty acids, but it doesn't keep contamination away. Potassium sorbate is good with yeast and fungi, but isn't good with bacteria, which means you're leaving yourself open to some serious beastie growth! (What contaminants can get into our products?) I suggest finding a broad spectrum preservative that offers protection against all possible contaminants!

Let us know how the next batch turns out!

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