Many people use oils (ideally cold pressed organic 100% pure) as a replacement of skincare, or as a step in it. Yes, such words as organic, all natural, full of vitamins and minerals sound really good and people leading organic lifestyle propagate the usage of those. You know, there are oils that can clog your pores. They do so by increasing follicular hyperkeratosis—an increased production of keratin in hair follicles. Over time, this leads to clogged follicles and comedones. Thus, oils with a low comedogenic score are safe to use. This is nothing I’m going to talk here about. So, what are these beloved avocado, rosehip seed, grape seed, hemp seed, olive, safflower, coconut, etc oils? Well, 60% of each are fatty acids. Among these, in the vast majority of cases, 95% are linoleic and oleic acids (pic1; CENTERCHEM, Inc. NOEWALK) Thus, oils are concentrated chemical solutions. Linoleic acid (18:2) is scaled by NFPA 704 as level 2 hazard to health (0-4), meaning intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury (e.g. diethyl ether, ammonium phosphate). The next point on the scale is this one: 3 - short exposure could cause serious temporary or moderate residual injury (e.g. liquid hydrogen, carbon monoxide, calcium hypochlorite). Oleic acid (18:1) is scaled 1 by HMIS: - exposure would cause irritation with only minor residual injury (e.g. acetone, sodium bromate). Safety data sheets in chemical/biochemical labs state: Adverse Human Health: Material may be irritating to the mucous membranes and upper respiratory tract. Effects and Symptoms: May be harmful by inhalation, ingestion, or skin absorption. May cause eye, skin, or respiratory system irritation. Indeed, 1 of 2 people is sensitive to even organic cold pressed natural oils and develop the worst irritation and breakouts they have ever had in their lives. Sometimes without even knowing what causes this state.
WHY? WHY ARE THEY SO IRRITATING TO SOME PEOPLE AND WHY DO THEY MAKE OTHERS SKIN VERY SOFT AND SUPPLE?
Answers hide in the nature of fatty acids and how they act when applied topically. Remark: our cells are surrounded by membranes the main component of which is a lipid bilayer (see pictures below). There are organelles in cells which have their own membranes. The composition of those differs, but the base of all membranes is the same lipid bilayer. Studies show that even micromolar concentrations of palmitic (C16, saturated acid) and oleic acid incorporate into the sarcoplasmic reticulum membrane (an inner cell organelle, surrounded by lipid bilayer) and reduce the content of phospholipids in the membrane. (pic2 - representation of fatty acids penetrating a lipid bilayer; Leo G et all, 1983)
A consequence of enhanced skin permeability and/or toxicity with fatty acids is increased transdermal water loss (lauric, oleic acids). The intercellular lipids (permeate through the whole membrane) have an important function in maintaining the barrier to water permeation through the skin and for holding water in the skin, removing of intercellular lipids produced chapped and scaly skin.
Maximum permeation enhancement was observed for fatty acids of 9 to 12 carbon atoms and for fatty alcohols of 10 to 12 carbons. Among saturated fatty acid, the maximum enhancement was shown by lauric acid (C12). (M. Loden at all, 2000)
So, fatty acids actually promote a water loss but give us a filling of soft and hydrated skin. Note that, when tests say the maximum or elevated score they don’t say other substances scored 0, as permeation ability was shown for many other fatty acids, as myristoleic, palmitoleic, linoleic, oleic, lauric and many others. Let’s be clear. The skin permeation effect of fatty acids indeed depends on the chain length and saturation. But the thing is oils do not contain very short fatty acids or contain only trace amounts of those (chains of very very short fatty acids are too short to incorporate into the lipid bilayer, therefore didn’t show irritation reactions). Also, it’s not the deal with a specific membrane, as all of them have the same basis. In an irritation test in nude mice, 10% oleic acid caused severe irritation. Oleic acid was also evaluated in guinea pigs, with 5% producing significant epidermal damage. Various fatty acids have been examined in humans by applying for 3 h under occlusion using concentrations 0. 16 M. Oleic acid resulted in an elevated score and visible erythema and edema. (M. Loden, 2000). Thus, all caused some damage, but oleic acid - an elevated effect. Another study shows linoleic acid produced significant irritation on human skin (Michael A et al, 1975). Also, prior studies on the relative irritancy of free fatty acids revealed the saturated C8 to C14 fatty acids and a C18 unsaturated fatty acid to be the most irritating. Another study says that among saturated free fatty acids from C3 to C18, and unsaturated C18 free fatty acids that were applied daily under occlusive patch tests to human skin until detectable erythema appeared, the most irritating fatty acids were C8 through C12. Of the unsaturated fatty acids tested, only linoleic acid produced irritation ( it was the only tested, though). Also, notice that different tests tasted different fatty acids and therefore one can say the most irritating was this acid/only this acid showed irritation, while an another test names different acid due to different samples included. Studies say they applied oils until the detectable erythema occurred, thus erythema occurred in all applied saturated fatty acids. Among these, they evaluated the most irritating samples. SO WHY OILS ARE SUCH GOOD CARRIERS? All people say oils are good natural carriers of vitamins and minerals to the skin. Oh yes, they are very good carriers, as they disrupt lipid bilayer (a membrane that surrounds our cells) incorporating in it and therefore make it easier for other substances to penetrate through it. But our skin is not designed as frogs skin, which consumes near 10% of oxygen within it. Our skin is a barrier, nourished by minerals, vitamins and fatty acids, etc supplied by blood, thus there is no need to disrupt the natural barrier in order to deliver minerals and vitamins topically. But even people that develop skin irritation and breakouts can safely consume different types of oils. Even mice like food flavoured with oil more. What’s the secret behind it? The thing is our digestive tract has a layer of mucus that protects it, also it regenerates really fast and digests all sort of organic compounds starting from our mouth. WHY DO SOME PEOPLE DEVELOP IRRITATION AND OTHERS NOT? Let’s look at one example. There is a compound called PTC (phenylthiocarbamide). It has an extremely bitter taste. Evolution gifted us an ability to detect bitter tastes because at the most cases bitter means toxic. So, when you can distinguish many bitter substances, you have better chances of survival. But turns out that we vary in the ability to taste PTC and among different nations and populations only certain amount of people can taste it (from 16% to 40%). But it doesn’t mean for those who can’t distinguish the taste, it’s beneficial and they can eat it without consequences. The same is with topical irritation. Not everyone develops the reaction, but it doesn’t mean it’s beneficial for those (we are not talking about allergies here, just irritation!) Most people experience some sort of reaction after some time of continuous application, as irritation may be induced by repeat disturbance of barrier function. The immune system reacts to this disturbance and et voila, acne occur! Maybe you also wonder how oils helped some people to battle acne (especially oil cleansing method) It turns out, they aren’t sensible to the mechanism in which fatty acids act. Okay, fatty acids act the same on their skin, they just don’t develop a visible reaction to it. Thus, fatty acids could dissolve makeup traces that can irritate their skin, or dissolve natural sebum, rich in oleic acid (true for those who has acne) that clogs pores and not to cause irritation by itself. Also, in the vast majority of cases, these people take a holistic approach to their acne and stop eating dairy, take Accutane, cure hormone disbalance, etc, so it's not necessary the oils cured their acne. WHY DO PEOPLE BELIEVE USING OILS TOPICALLY IS GOOD FOR SKIN?
1. People are leaded by the fact that linoleic acid is a natural component of human sebum.
Let's investigate. See pic3 below. (Mauro Picardo et all, 2009) Triglycerides and fatty acids, taken together, account for the predominant proportion (57.5%), followed by wax esters (26%) and squalene (12%). The least abundant lipid in sebum is cholesterol, which with its esters, accounts for the 4.5% of total lipids. (Greene RS et all, 1970)
Now, see a pic4 below. (B. Boughton et all, 1959) Remark: Index a means saturated acids, b – mixture monounsaturated and single branched acids, c – mixture of highly branched acids and more highly unsaturated acids. We can see, that linoleic acid (18:1) and oleic (18:2) acids are only less than 15% (there are also different linear monounsaturated acids with 18 carbons) of all fatty acids (they are 57.5% of sebum), thus less than 9 % of sebum are linoleic and oleic acids together. It’s not healthy smearing concentrated fatty acids on your skin, even though it’s produced by sebaceous glands in some quantity naturally. Most people imagine human sebum as a blend of fat and some small amount of water. It’s not like this at all. Think about this: we can obtain not only oils from seeds but cyanide too. It will be 100% natural and organic, but would you smear it all over your skin? (the toxicity isn’t relative, but It’s just an example that not everything obtained from plants is good for health).
Indeed, human sebum is a unique substance, that can maintain itself when supplied with essential by blood (by the food we eat). (You can actually skip this paragraph) It is unique in particular, the pathways leading to the formation of lipids, which are typically sebaceous, such as branched fatty acids and fatty acids with unshared unsaturation positions: features unique to sebum are the branched chain fatty acids and lipids with a particular pattern of unsaturation. Δ6 desaturase enzyme (fatty acid desaturase-2) catalyzes a “sebaceous-type” reaction of desaturation that leads to particular compounds, unique to humanΔ6 desaturase preferentially converts palmitic acid (16:0) to sapienic acid (16:1, Δ6), which is unique to the human sebum and represents ca. 25% of the total fatty acids. Elongation of sapienic acid by 2-carbon unit and further unsaturation leads to the formation of sebaleic acid (18:2, Δ5,8), which is also peculiar of human sebum. (Ge L. et al, 2007) We cannot deliver fatty acids that are synthesised only by human cells topically (at least if you don't plan to extract them from some human body...) 2. People that don’t develop any kind of visible bad reaction experience very soft, “hydrated” skin.
Of course, skin is soft after continous apзlication of oils, as they disrupt elastic membranes and make skin very supple in that way.
There is one Polish saying “co bagato, to niezdrawo”, meaning when there is too much of something it’s not helthy. Even though vegetable, seed, nut oils are all natural, this doesn’t mean they can replace human sebum and can be used safely on the skin. We have a need in linoleic acid, but mainly in our food or some severe conditions that demand topical application of oils (can be helpful for people that don’t develop visible irritation).