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!