Tuesday, May 24, 2016

One ingredient, five products: Stearic acid

Poor stearic acid. It's often overlooked for its glidier, silkier cousin cetyl alcohol, but this fatty acid is an inexpensive way to thicken a lotion, anhydrous body butter, lotion bar, and more.

Stearic acid is a saturated, long chain fatty acid with 18 carbon molecules, which is to say it is a chain of carbons and hydrogens with a carboxyl group (that COOH you see at the end of the chain) at the head. It's called an acid because this carboxyl group is called a carboxylic acid. It's found in most of our oils and butters, and can be found in the human body in our muscles.

It isn't an emulsifier, but it can help to stabilize an emulsion and it's a great thickener for our lotions. It is considered as part of the oil phase in the HLB system - its HLB value is 15.5 - and it has a melting point of 69.6˚C, which is why we must heat and hold our lotions at 70˚C or higher when using stearic acid. (We should do this all the time, but it's especially important when we're using stearic acid or a butter or oil that contains stearic acid!)

Related posts:
Why do we heat & hold our lotions?
Why do we heat & hold anhydrous products?

There is an emulsifier you can make from a combination of stearic acid and triethanolamine (TEA). (As an aside, Lush uses this emulsifier all the time in things like their Dream Cream and Helping Hands lotion.) These combine to make an alkaline soap that emulsifies oil in water. I have never tried this combination before, so I'll refer you to this great article about vanishing creams and how to make this emulsifier!

I know I mentioned this a few paragraphs above, but I think it bears repeating: Stearic acid on its own isn't an emulsifier. When combined with TEA, it creates a type of soap that can emulsify. You can't just use stearic acid as an emulsifier as it will fail. 

You're probably quite familiar with how to use stearic acid in lotions if you've read my blog for any length of time. It's suggested to include it in the heated oil phase at up to 5%, but I like to use it at 2% to 3%. The more you use, the thicker the product will be. You can add it to shampoo and conditioner bars to make it more solid, although cetyl alcohol is probably a better choice as it works in conjunction with the cationic quat compounds to offer more conditioning. Because it is saturated, it is considered resistant to rancidity, so it's got a long shelf life.

Why use stearic acid as a thickener? It's inexpensive and has a long shelf life. You could thicken a lotion with 5% butter, but 3% stearic acid will be more effective and much cheaper than any butter you find.

Why use it instead of cetyl alcohol? It's great for products where you want a lot of thickening, like a foot or elbow cream. It easily changes your body butter into a more tenacious cream. Yeah, it can be more draggy than a fatty alcohol, but do you care about that if it makes your cream stay on longer?

It also offers a slight cooling sensation, which is another reason I use it in my foot creams!

There are a few down sides to using stearic acid. The first is that slight draggy feeling you get when you apply it. I don't really mind it all that much, but some people say they don't like that skin feel.

The other is the potential for the soaping effect. This is when you get that white film on your skin after applying your lotion. You can compensate for this by using dimethicone at 2% to 3% in the cool down phase of the lotion, use less lotion on your skin, or not really worry about it as it's just there for a few minutes, then it goes away!

Related posts:
A few questions about stearic acid

Join me tomorrow as we take a look at how we can use stearic acid in a lotion! 

8 comments:

Anita said...

I've yet to use stearic in any products, but it's invaluable in shave soap so I have a supply on hand, and I've been meaning to make a thick foot cream.

I believe a correction needs to be made though. Under the "Why use it" you state that it's inexpensive and has a short shelf life. This comes after the previous paragraph where you state it's got a long shelf life.

~Mrs Spaceship.

Susan Barclay-Nichols said...

Corrected it! Thanks!

Christine Montano said...

I really appreciate your blog. Would you please clarify do to tricky sentence placement and wording I am unclear if you are saying that lush uses only stearic acid in their dream cream or do they use stearic acid and TEA together? If you could edit the sentence instead of saying "this emulsifier" to just state the name of the emulsifier it would be more clear. Thank you.

Susan Barclay-Nichols said...

HI Christine. Stearic acid on its own isn't an emulsifier. It's part of an emulsifying system we create by combining TEA and stearic acid. If you were to use it in a lotion, you'd say "I created an emulsifier from TEA and stearic acid", as it doesn't have a name. It is a type of soap, so I guess you could call it an alkaline soap emulsifier, but no one does.

Does this modified version offer more clarity?

There is an emulsifier you can make from a combination of stearic acid and triethanolamine (TEA). (As an aside, Lush uses an emulsifier made from stearic acid and TEA all the time in products like their Dream Cream and Helping Hands lotion.) These combine to make an alkaline soap that emulsifies oil in water. I have never tried this combination before, so I'll refer you to this great article about vanishing creams and how to make this emulsifier!

I know I mentioned this a few paragraphs above, but I think it bears repeating: Stearic acid on its own isn't an emulsifier. When combined with TEA, it creates a type of soap that can emulsify. You can't just use stearic acid as an emulsifier as it will fail.

Susan said...

Hi Susan,
Loving the articles on Stearic Acid - They've inspired me to make a foot cream this week with some menthol, thought that would be awesome for the summer!

I made a lotion today and it was an epic fail, again! I have made this lotion many times without a problem. The last two products I have made have failed with the same issues happening. The first was a facial cream (that I have made before without an issue) and I just thought that perhaps I did something wrong, but couldn't exactly put my finger on it. Today I made a lotion that I have been making for years without fail. Its very thick and great for after the shower. I often change out the oils to change it up a bit, but that's about it. My recipe is for a larger batch in grams (frown on the waste today) ... but I have converted it to % here:

Water Phase:
66% distilled water
3% Glycerin
1.5% Optiphen Plus

Oil Phase:
8.7% Coconut Oil
5.2% Sunflower Oil
2.3% Raspberry Seed Oil
2.3% Sesame Seed Oil
1.4% Beeswax
5.5% Emulsifying Wax
1.8% Stearic Acid
.3% Grapefruit Seed Extract
1% Vitamin E
1% Fragrance

In the face cream, and this lotion, they both emulsified beautifully initially, and then when poured into containers, a waxy top formed. Today I noticed the waxy top forming even before I poured it! Being wax, I wondered if perhaps it was my E-wax or Stearic acid? Those are the only two products that I have recently purchased. I hesitate to make another lotion to have yet another fail, so thought I would bounce this off you in case you have ever experienced this? If it appears to be one of these products (perhaps a bad batch from the supplier?), I will just get new product and try again. The face cream I made also had some Cetyl Alcohol in it, so I thought that might be a culprit to, but now I think not, since this recipe does not have it.

Thoughts?

Thanks again!
Susan in Calgary

Susan Barclay-Nichols said...

Hi Susan! I don't know what e-wax you're using or your method, so I'll go with the easiest answer, which is that Optiphen and Optiphen Plus are known emulsion destabilizers. I'll refer you this post on the topic and encourage you to check out the comments. This is one of the main reasons I don't recommend these preservatives to readers of this blog.

As well, you need more e-wax. Generally we use 1/4 the oil phase plus 1% more for e-wax.

Susan said...

Hi Susan,
Thanks so much. I didn't realize that Optiphen Plus would do that ... I only switched recently to try Optiphen Plus, but I do have Phenonip, so perhaps I will use that next go round. I was using E-Wax NF and following general lotion making (heat and hold, emulsify, etc.) Fragrance added to cool down phase.
Thanks for the info on Optiphen, and the direction to the post - I really hadn't thought of that!

Next batch will be Phenonip!!
Thanks again, Susan

Miri Pardo said...

Hi Susan!

I've been looking for the recipe for the anhydrous lotion bar with stearin acid, but I can't seem to find it. I thought my little boy might like to play scientist (with me, of course!) and turns solids into liquids into solids!

Thanks!

Miri