I'm so confused!! I'm going in circles and about to pull my hair out! I'm trying to understand fatty acid profiles. I get double bonds and saturated versus unsaturated in terms of a fatty acid chain. And, I understand what fatty acid profile tells us in terms of shelf life of an oil. But, I'm confused about what else it tells me.
For example, oleic acid (monounsaturated - omega 9 - C18:1) - not an EFA, helps with cell regeneration and provides skin softening properties, and is also moisturizing. My question is how does it do that? What's the mechanism? Is it related to fatty acid synthesis and the pathway in metabolism? And why is oleic acid regenerative as opposed to linoleic acid which is said to restore barrier function.
Linoleic acid (duo-unsaturated - omega 6 - C18:2), an EFA, helps restore barrier function and acts as anti-inflammatory that can help with dry and itchy skin; can reduce TEWL. How does linoleic acid work as an anti-inflammatory? Is it because it has 2 double bonds? Is it related to the conversion of linoleic acid to GLA and AA?
What differentiates the two in terms of how they work? Is it because one has only one double bond and the other has 2? They're the same chain length. So, I don't understand what makes one provide cell regeneration and the other restore barrier function?
Why do oils go rancid? Check out this post to learn more!
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. 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.
Why is linoleic an essential fatty acid (EFA)? It's considered essential because we need it to live. We can't produce it, so we must get it from outside sources, like sunflower or soy bean oil. (You may also see it called a polyunsaturated fatty acid, meaning that it has more than one double bond.)
stratum corneum liquids make up about 15% of the dry weight of the stratum corneum, and contain about 40% to 50% ceramides, 20% to 25% cholesterol, 15% to 25% fatty acids (those with C16 to C30 chain lengths, with C24 to C28 being the most common), and 5% to 10% cholesterol sulfate.
So to answer the question, the reason it helps with barrier function is because it's found in the lipids of our stratum corneum. Without linoleic acid in our skin, we would experience essential fatty acid deficiency, which leads to increased transepidermal water loss, skin dryness, and inflammation of the skin. Adding it back in the form of something like sunflower oil means our skin will incorporate it as part of the stratum corneum lipids, leading to an increase in barrier function, which leads to a reduction in transepidermal water loss and reduction in dry skin. The reason oleic acid doesn't help with barrier function is that it isn't part of our skin's normal make-up, so applying it topically doesn't change the make-up of our skin's barrier lipids, which leads to the increase in barrier function.
How does linoleic acid work as an anti-inflammatory? There are chemical messengers in our skin called eicosanoids that play critical roles in inflammatory and immune responses in our skin. They are produced by enzymatic reactions between LOX enzymes and linoleic acid to produce hydroxy fatty acids, like 13-hydroxyoctadecdienoic acid, that has anti-proliferative effects. Linoleic acid is converted to gamma-linoleic acid, then to dihomo-GLA, then to arachidonic acid. Along the way, dihomo-GLA produces 15-HETrE, which is anti-inflammatory, and arachidonic acid produces 15-HETE, which is also anti-inflammatory.
So the answer is yes, it is an anti-inflammatory because of the conversion of linoleic acid into gamma-linoleic acid, dihomo-GLA, and arachidonic acid.
Does linoleic acid act as an anti-inflammatory because of the two double bonds? Sort of...The 18 carbons and double bonds in the 6 and 9 spaces define this molecule as linoleic acid. Take away the 6 double bond, you have oleic acid. Add a double bond at 12 and you have linolenic acid. So I think the answer is kinda yes because if it didn't have these two double bonds in just the right place, the molecule wouldn't be linoleic acid.
Join me tomorrow as we take a closer look at oleic acid!
The repair of impaired epidermal barrier function in rats by the cutaneous application of linoleic acid
Permeability barrier in essential fatty acid deficiency: Evidence for a direct role in linoleic acid in barrier function