It’s Michelle of Beauty Science here again with more skin care related chemistry nerdery. Today we’re going to be discussing a misconception that’s quite common in skincare communities. It’s about fatty acids and oils. Ihis might sound really abstract and theoretical but it’s fundamental to understanding why some claims about oils aren’t as valid as they sound. For example you might see lauric acid is 15 times better at killing acne bacteria than benzoyl peroxide. Coconut oil is 50 percent lauric acid, so coconut oil is going to be fantastic at killing acne bacteria. Or oleic acid disrupts your skin barrier. Since argan oil contains about 50% oleic acid it will disrupt your skin. But chemistry and biology say otherwise. Let’s chat about fatty acids and triglycerides. An acid in organic chemistry is a group that contains a carbon double bonded to an oxygen atom and an OH group. This hydrogen can ionise which is what makes it an acid. Fatty acids have this acid group connected to a long non-polar hydrogen and carbon chain. This chain makes the chemical feel greasy and fatty, hence the name fatty acid. There are a range of fatty acids. Yhere are saturated fatty acids which contain no double bonds like lauric, myristic stearic and palmitic acids. There are monounsaturated fatty acids that have one double bond like oleic and sapienic acid, and polyunsaturated fatty acids that have multiple double bonds like linoleic and linolenic acid. Some unsaturated fatty acids are called omega fatty acids.
Skincare Oils and Free Fatty Acids The Science Beauty Science Photo Gallery
The omega refers to where the double bonds are. A triglyceride also known as a triacylglycerol looks like this. It has one glycerin molecule connected to three fatty acids via what are called ester linkages. Triglycerides are the main components of the common fats and oils that you’ll know: the vast majority of plant oils like olive oil, sunflower oil, coconut oil, but also fats like beef fat and lard. If you zoom into the ester linkages in a triglyceride you’ll notice that the COOH acid groups aren’t there anymore. There technically aren’t any fatty acids in the triglyceride at all! That’s because the acids have undergone a chemical reaction to make the triglyceride so they’re no longer acids. So what happens is this OH on the fatty acid comes off and a hydrogen on the glycerin also comes off, and they connect like that. So you can see the acid no long has that H+ that can come off, and so it’s no longer an acid. It’s a little bit like how sodium metal and green chlorine gas undergo a chemical reaction to give sodium chloride, which is white and salt and delicious, not green or metallic or gas-like at all. But chemical reactions can be reversed under the right conditions. That’s why you’ll see lots of nutritional advice saying that fish oil is a good source of essential omega-3 fatty acids, even though the actual fish oil contains only triglycerides. Lipase enzymes from your saliva, stomach and pancreas break up the triglycerides and turn them back into free fatty acids.
This breakdown reaction is called hydrolysis. Soap makers also talk about oils in terms of the percentages of fatty acids contained in them, because the main step in soap making involves performing a chemical reaction with lye to break up the covalent bonds in the triglycerides to free the fatty acids. But plant oils contain very little free fatty acids. In general you’ll have less than 1% free fatty acids in the oil that haven’t been either transformed into the triglyceride or have broken off the triglyceride. Too many free fatty acids actually makes the oil rancid which is when it smells and tastes off. For example coconut oil can’t be sold if it contains more than 0.5% free fatty acids. Virgin coconut oil has an average of 0.1 percent free fatty acids. Cold-pressed unrefined rose hip oil has about 2% free fatty acids. So when we put oils on our faces we’re applying very little free fatty acids. So the question is: do we have lipases on the surface of our skin that can break up these triglycerides? If yes then using oils is the same as using the free fatty acids, but if not then it’s like going to a restaurant and ordering a steak and being given the steak while it’s still attached to the cow. It turns out that the answer is quite complicated. I’ve actually been wondering about this and reading about it on and off for about three years, and I’ve been talking to my nerd friend/cosmetic chemist Stephen about it a few times and I finally sat down and read through hundreds of references before coming to a conclusion that I’m somewhat confident with. I’ve included the most relevant references here, but if you’re really interested in the science and the chemistry behind it all I’d encourage you to do a proper literature review yourself. There are enzymes called lipases in your skin that can break up triglycerides. Some of these are made by humans but a ton of these are made by microorganisms living in your skin. Most of these live under the surface of your skin in your pores. Humans produce an oil called sebum in the sebaceous glands under the skin.
When it’s at the bottom of the pore near the sebaceous gland it contains a high amount of triglycerides and almost no free fatty acids, but by the time it gets to the skin’s surface around 1/4 of this has broken up to give 15% free fatty acids. Scientists in the 70s did some experiments and found that P acnes, the acne bacteria, is the main microbe that produces these lipase enzymes that break down the triglycerides, but other species can produce lipase enzymes too. For example Malassezia fungus, staph and corynebacterium. The vast majority of these organisms and their lipase enzymes sit inside the pores. There’s also a lipase that your body makes in the living epidermis of your skin that then gets released into the stratum corneum with the rest of the lipids. So there are lipases and theoretically they can break down the triglycerides to give free fatty acids but how much and how fast? There aren’t that many studies that we can look at to see how much and how fast triglycerides get broken down to give the free fatty acids when they’re applied to the surface of your skin, so here’s what I’ve managed to find. In the 1950s there was a radioactivity study where radioactive tripalmitin which is the triglyceride of palmitic acid was applied to someone’s back for two and a half hours then wiped off and analysed. 6% of the radioactive tripalmitin was broken up versus approximately 30% of the triglycerides in regular sebum. So why was this figure so low? The scientists who did this experiment suggested that it was likely that the oil on the surface couldn’t get into the pore whether lipase enzymes were, and even if it did it would probably get pushed out by the new sebum that was coming out of the sebaceous glands. 6% in 2.5 hours sounds like quite a lot especially when you think about how long oil stays on your skin overnight, but only a really tiny amount of the tripalmitin was used in this experiment. It was 0.5 milligrams which converts to 0.56 microliters. One drop of water is about 50 microliters so this is one hundredth of a drop, which was applied over 300 square centimeters which is about this much skin. If you use more oil then it’s even less likely that it’ll get into the pore and so you’ll have an even lower percentage. Another study used mixtures of oleic acid as the free fatty acid and glycerol trioleate which is 3 oleic acid molecules bound up, bonded to glycerin.
Oleic acid as a free fatty acid is known to be a barrier disruptor. They made a bunch of mixtures that were 0% free fatty acid and 100 percent triglyceride; 25 percent free fatty acid; 50 percent free fatty acid and 100 percent free fatty acid. They applied one drop of each mixture to the forearms of 12 people, covered it with gauze, gave them plastic wrap so they could cover it while they were showering, then looked at the sites the next day. First they measured the trans epidermal water loss or TEWL which is the leakiness of the skin to water leaving. They found that the sites with 100% triglyceride had no change from the untreated areas of skin. The trans epidermal water loss for the rest of the sites was directly proportional to the amount of free fatty acid oleic acid. The scientists also measured how easily chemicals could penetrate the skin going in using fluorescein dye. The depth of the penetration of the dye was proportional to the amount of oleic acid as well. So these results suggest that only very negligible tiny amounts of triglyceride were actually broken up into the free oleic acid or at least anything that was broken down to give oleic acid was immediately turned into something else that didn’t disrupt the skin barrier, or perhaps they just didn’t end up in the same place. Applying free oleic acid and applying oleic acid bound up in triglycerides definitely did not have the same effect, at least within the time frame of the experiment which was 24 hours. There was a third study which was a longer-term study. In this study they made a cream which contained linoleic acid-rich oils which were sunflower and borage seed oil. There was also a plain placebo cream and both of these cranes were applied to dry skin in winter. They were applied twice daily for four weeks on the inside forearm of eleven different people. Each person applied the active cream to one arm and the placebo plain cream to the other arm, then afterwards the scientists analysed the lipids in the stratum corneum. They looked at the ceramides, free fatty acids and cholesterol content after four weeks.
They found that there was actually less free fatty acids in the treated area compared to the plain cream but they found that the levels of ceramide 1 linoleate which are ceramides with linoleic acid attached were nearly doubled on the treated part compared to the plain cream, while the same type of ceramide but with oleic acid attached was much lower. It’s also worth noting that in sebum in the free fatty acid portion there’s actually less unsaturated acids like linoleic acid and oleic acid than in the original triglycerides. So what this suggests is that some free fatty acids, linoleic acid and oleic acid, are selectively removed after triglycerides are hydrolyzed or broken down, and used to make other substances like ceramides. So what does this mean? From these studies we can see that triglycerides applied on skin aren’t broken down to give you free fatty acids on your skin. This is important because in pharmacology the dose is very important. For example if you take one ibuprofen painkiller tablet it’s less effective than taking two. Taking one ibuprofen pain tablet might get rid of your headache, but taking tiny portions of one tablet over three days won’t be noticeable. It’s even more complicated because breaking down the triglycerides depends on microorganisms and different people have different microorganisms on their skin. For example men have more microbes on their skin than women and other factors like climate and genetics will make a big difference too.
Different parts of your face and body also have different microorganisms. One study found that sebum triglycerides were hydrolysed more quickly at the nose than on the forehead. Taking antibiotics will change your skin’s microbes obviously, but so will other things like using different cleansers, creams and antibacterial products. So in conclusion we shouldn’t rely on oils for the properties of their free fatty acids, unless they’ve been shown to be effective at very low concentrations, although having them in an oil and having them in a solution of alcohol, which is how they usually test the activity of these free fatty acids, will have very different effects on how well they penetrate your skin. But this doesn’t mean that all oils are useless. They can still be very beneficial for example oils are often excellent moisturizers. They can be occlusive and slow down how quickly water leaves your skin and make it dehydrated, plus they work as emollients that soften your skin. They are also very good bases for oil soluble ingredients and sometimes they naturally have beneficial ingredients in them. For example rosehip oil contains a few forms of vitamin A mostly beta carotene but there’s also a tiny amount of retinoic acid or tretinoin in there as well. They can also potentially be good sources of fatty acids for making ceramides in your skin as shown in the study on sunflower and borage seed oils. So in summary oils contain fatty acids bound up in triglycerides, not free fatty acids. Applying skin care oils won’t give you the same effect as applying the free fatty acids. That’s all from me today! If you like my posts I’d love it if you could comment to my My blog and like my posts. I also have a blog where I have lots and lots of beauty science. You can also follow me on Facebook and Instagram where I post lots and lots of skincare tips based on science. See you next time! :).
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