Interesting research
Free Fatty Acids
INCI: Linoleic Acid, Palmitic Acid, Stearic Acid · also FFA, essential fatty acids, linoleic acid
The third lipid family in the barrier, and the smallest share of the three. Linoleic acid is the one that cannot be made from scratch by the body, which is why it is called essential.
Why it is here
The smallest share of the barrier and the one you cannot make yourself. Too much of it slows repair, so this is the one ingredient where we were careful not to be generous.
Free fatty acids acidify the stratum corneum surface and contribute to lamellar packing. Linoleic acid does something more specific: it is esterified into acylceramides, the long ceramides that rivet the lipid sheets together, so a shortage of it destabilizes the whole structure. In essential fatty acid deficient rodents, topical linoleic acid restored barrier function at the site of application before the systemic deficiency was corrected.
The receipts
Topically applied linoleic acid rapidly reversed the barrier defect at the sites of application before systemic correction of the deficiency, and did so whether or not prostaglandin synthesis was blocked, indicating a direct structural role rather than a prostaglandin-mediated one.
The permeability barrier in essential fatty acid deficiency: evidence for a direct role for linoleic acid in barrier function. Journal of Investigative Dermatology, 1980. in vivo animal, n = essential fatty acid deficient mice. PMID 7373078
Free fatty acids are one of the three lipids required for permeability barrier homeostasis; either linoleic acid or the non-essential palmitic or stearic acids worked in equimolar mixtures, and neither phospholipids nor cholesterol esters could substitute for them.
Optimization of physiological lipid mixtures for barrier repair. Journal of Investigative Dermatology, 1996. in vivo animal, n = murine skin, with preliminary validation in damaged human skin. PMID 8618046
In practice
- Typical use
- 0.1 to 1 percent as part of a physiologic lipid mixture. The published work is clear that the proportion relative to ceramides and cholesterol matters more than the absolute figure.
- Keep apart from
- Fatty acid dominant lipid blends on aging skin: in the 1997 aged-skin study a free fatty acid dominant mixture significantly delayed barrier recovery. This is the one lipid where more is documented to be worse.
- Cautions
- None notable at formulation levels. Free fatty acids can oxidize, which is a stability and smell issue rather than a safety one, and is why well made lipid creams also carry an antioxidant.
Questions people ask
Why is this in the interesting tier when ceramides are in good?
Because the direct evidence for free fatty acids on their own is rodent work from 1980, and the human validation exists only for the complete three-lipid mixture. The fatty acid is essential to the system and the system has human data. The isolated ingredient does not. We separate those two statements on purpose.
Is linoleic acid the same as the oil in my kitchen?
The molecule is the same one that makes up most of safflower and sunflower oil. But dietary oil is triglyceride, three fatty acids bound to a glycerol backbone, and the barrier work is on free linoleic acid delivered in a physiologic mixture. Cooking oil on your face is not the same experiment.
Does eating more omega-6 help my skin barrier?
Frank essential fatty acid deficiency causes a real, visible barrier defect, and correcting it systemically fixes it. But almost nobody eating a normal diet is deficient, and there is no good evidence that pushing intake higher improves an already sufficient barrier. The topical work is about local delivery to damaged skin.