Thursday, October 22, 2009

Linoleic acid

As an introduction to looking at the various oils we can use in making our bath & body products, I thought I'd take a look at the various fatty acids on their own and see what they bring to the mix...and linoleic acid (C18:2 or octadecadienoic acid ) seemed like a good place to start. And what a place to start! I think a person could do a PhD dissertation on this fatty acid! It's found everywhere, and it's essential for our skin and body to function.

Linoleic acid is considered an essential fatty acid, one we can't construct ourselves in our body, so we have to get it from the outside world. It is crucial to normal barrier function in skin, and a deficiency can lead to dry skin and hair, hair loss, and poor wound healing. It is a major component in ceramides - about 14% - which make up about 50% of our stratum corneum or outer layer of skin.

Ceramides are essential for the normal organization of our tissues into structures that are responsible for keeping the barrier function of the skin functioning well, like preventing transepidermal water loss and keeping other things out. They are found in our skin at about 50% by mass. The other components of our skin are fatty acids (10 to 20% by mass) and cholesterol (about 25%). A decrease in ceramides - through aging, exposure to high or low temperatures - can lead to dry skin and itchiness due to a decrease in the efficacy of the stratum corneum's ability to keep water in and other things out.

Note: To make a moisturizer and call it filled with ceramides, you have to follow the ratio above of 50% linoleic acid, 10% free fatty acids, and 25% cholesterol. I'm not making the claim any of the following recipes contain ceramides as I won't be actively including the free fatty acids or cholesterol.

During the winter, a proportion of our ceramide 1 linoleate (acylceramide) decreases, and this can lead to dry and itchy skin. During the summer, our skin has increased levels of palmitic and palmitoleic fatty acids. And people with atopic dermatitis and acne show reduced levels of linoleic acid in their skin.

Studies have shown linoleic acid can restore the barrier function and reduce scaling on your skin. One study showed using linoleic acid on people with acne reduced the pustule size by 25% in one month. It can act as an anti-inflammatory, acne reducer, and moisture retainer.

You can eat your linoleic acid in the form of fats and you can put them directly on your skin for maximum lovely benefits!

The one problem with linoleic acid? It's a polyunsaturated fatty acid (C18:2), so most of the oils in which we'll find it are going to have short shelf lives. We can choose ones with longer shelf lives - like rice bran oil - or add anti-oxidants and chelating ingredients to our lotions. (Or just accept we're going to have a short shelf life product and make a note of when to throw it away!)

Sunflower oil contains 61 to 73% linoleic acid with a shelf life of about 6 months. The high oleic versions will last a year, but they only contain about 3 to 9% linoleic acid. As a note, sunflower oil contains about 630 to 700 mg Vitamin E per kilogram (which is quite a lot), so this explains why something with such a high ratio of double bonds can last 6 months!

Safflower oil contains up to 70% linoleic acid, but again its shelf life is about 6 months.

Rice bran oil contains up to 37% linoleic acid and 42% oleic acid (more on this shortly) and up to 400 mg per kg tocopherols, giving it a long shelf life of about a year. It also contains Vitamin B, Vitamin E, and squalane.

Sesame oil contains up to 40.4% linoleic acid, and is a longer lasting oil thanks to the high proportion of oleic acid (C18:1). It is a medium weight oil and is good for massage oils as it won't stain clothes or sheets.

Soybean oil contains up to 51% linoleic acid, and contains up to 700 mg per kg tocopherols (mostly in the gamma tocopherol state, which is great for its anti-oxidant properties). This oil should last 9 months to a year thanks to those anti-oxidants.

Wheat germ and hemp seed are both awesome linoleic acid sources, but both have very short shelf lives - 3 to 6 months, if you add your anti-oxidants! Hempseed contains 57% linoleic acid, and wheat germ contains 55 to 60% linoleic acid.

Some our more expensive oils contain both linoleic acid and gamma-linoleic acid (more on this shortly). Evening primrose oil contains 9% gamma linoleic and 71% linoleic acid. Borage and black currant oils both contain high levels. And watermelon seed oil contains 60% linoleic, 20% oleic, and 20% palmitic and stearic acids.

So let's take a look at how we can create some lovely moisturizing products for the upcoming winter season (in the Western hemisphere at least!) using maximum amounts of linoleic acid!


Anonymous said...

Thank you very much for such an informative post! I am acne-prone and would like to try the OCM. I tried the olive oil (it didn't work out) and now I'm having some difficulties deciding which oil to use. I found a recipe of yours which seems ideal, but I don't have access to all of the ingredients & I'm not savvy enough to tamper with it. I think I'll settle with cold-pressed safflower oil; I hope I understood your article correctly. Again, thank you so much! (And excuse me for my bad english :)

Susan Barclay-Nichols said...

I wanted to list here a few studies you could check out on the topic of linoleic acid and barrier function...

Investigation into functions of fatty acids in skin
Permeability barrier in essential fatty acid deficiency
The repair of impaired epidermal barrier function in rats by the cutaneous application of linoleic acid
Lipids and barrier function of the skin
And so on...

Check out this post to see my general references and textbooks.

Jill said...

Thank you so much for this great information. I am formulating skin care products for my son who suffers from severe eczema, and also has quite a few food allergies. Knowledge is power!

Anastacia Zara said...

What's the difference between linoleic acid and alpha linoleic acid? (Not linoleNic) I can't find any information on the difference. Even Wikipedia doesn't have an article on alpha linoleic acid. Is this a typo that's driving me to the brink of insanity or is there really such a thing as alpha linoleic acid?

For context, here's the composition of Raspberry Seed C02 Extract:
Oleic Acid 11%
Linoleic Acid 53%
Alpha-Linoleic Acid 31%
Tocopherols 0,25%

Susan Barclay-Nichols said...

Hi Anastacia! I think it's a typo.

linda said...

i've been reading up on linoleic oils and it's interesting what you say about ceramides. i don't know what one was is but used to use an elizabeth arden ceramide face lotion and i never broke out from it. it was amazing but expensive and they have always been known for their skincare. also, a burt's bees lotion i really am liking, which is discontinued, is made with sunflower oil. i am going to try making my own lotion/lotion bar with sunflower oil high in the linoleic acids. thanks for all your helpful info.

Deb said...

Hi Susan; I have been studying your ebook Lotion Making 101; When you say that to make a moisturizer and say it is full of ceramides, you have to follow the ratio ... 50% linoleic acid, 10% free fatty acids and 25% cholesterol" I see that in the sections about oils you do list linoleic acid as a percentage but I am much less clear about the "free fatty acid" and "cholesterol". #1. Where do I find those percentages? #2. Where/what is the cholesterol I am looking for? #3. Are they percentages of the total oils? or is it just a ratio of specific parts of the oils. #4. I use ceramide powders (pre emulsions) recommended use at 1 gm in 120 mls of lotion. #5. How do I calculate this? I appreciate any thing you have to offer and thanks so much. Love your blog and book. deb

Susan Barclay-Nichols said...

Hi Deb! Thank you for your kind words!

You don't have to use those ratios - that's just something that was found in a study that was interesting.

As for information on free fatty acids, I've done a series about them. Start here, then click "newer post" to see the next installment.

You won't find information on free fatty acids in fatty acid profiles of oils.

Cholesterol is found in our skin. You can get it from animal products - for instance, using lard in our products, which I don't recommend - or from phytosterols in oil. (Phytosterols are the version of cholesterol we find in plants.) As well, you can get things like Super Sterol, which is a type of cholesterol. It's a lovely addition to a lotion.

You would calculate it as a percentage. 1 gm/120 ml = 0.83% in a lotion. (This isn't very accurate as you don't want mix volume and weight, but it's close enough. The problem is that making 120 grams of lotion isn't necessarily producing 120 ml of lotion, but this is close enough.)

Little Pieces of My Life said...

This might be a silly question, but I noticed a lot of oil based skincare products say that they contain the water-soluable vitamins like Bs, and C. How is that possible?

Nicole Pan said...

Hi Susan,

i've been obssessed by your posts! thank you for making it professional but so clear.
one question regarding the Note: To make a moisturizer and call it filled with ceramides, you have to follow the ratio above of 50% linoleic acid, 10% free fatty acids, and 25% cholesterol. I'm not making the claim any of the following recipes contain ceramides as I won't be actively including the free fatty acids or cholesterol.

why we have to add 10% free fatty acids and 25% cholesterol to make it work?