November 19, 2020
The Surfactant Guide – Part 1
by Leonie Poppe
So, today I would like to write about a topic that is very close to my heart. Besides UV protection, of course! :)
It's about cleaning the skin. Or rather, about cleaning it properly and what you should pay attention to when doing so. So that your skin really gets the best possible care that you can give it. So it's about surfactants, about their use as detergents and I'll also briefly look at their secondary business: surfactants as emulsifiers.
Because many of you may be wondering what surfactants really are, what they do to the skin and whether surfactants are perhaps even dangerous?
That's why I'm giving you 6 facts about surfactants that you should know so that you can better understand your cleaning products in the future and choose the right ones for you! 3 of them are in part 1. Let's get started!
#1 Surfactants are amphiphilic substances
Fig. 1
“Amphiwas” you ask? Amphiphilic means that the molecule has a part – in this case we call it the “head” – that feels very comfortable in water-like substances, or in water. The other part of the molecule, on the other hand, the “rest” here, loves fats and oily substances. Depending on the charge of the head and the greater the difference between the head and the rest, the more polar and active the surfactant is.
It also owes its areas of application and mode of action to this property. I found a really good comparison in Heinz Knieriemen's critical guide to cosmetic ingredients. Knieriemen describes surfactants as the little helpers of cosmetics. (1) I think this is a perfectly fitting term that does justice to the many possible uses of surfactants. You can find surfactants in soaps, shampoos and cleaning products for the skin, but also for household use. And we use them when mixing creams.
# 2 Surfactants act as washing substances and emulsifiers
Fig. 2
Because surfactants (from the Latin "tensus" = tense -> reducing surface tension) like both fat and water, they can combine these two substances, which actually repel each other. I always think of salad dressing. Shaken or stirred, if you let the dressing stand for a while, the oil always settles. In order to get a uniform liquid here, you would need a surfactant/emulsifier that reduces the surface or interfacial tension of the substances. But we'd rather leave that out of the salad. :)
An emulsifier is essential in creams. We need a substance that brings together vegetable oils, such as our argan oil, with water-soluble active ingredients such as hyaluronic acid. Tadaa – who would have thought, the hard-working surfactants take care of that.
They stick their heads in the hyaluronic acid, so to speak, and the rest grabs the argan oil, encloses it in small beads (see Fig. 2) and distributes it throughout the entire “mass”. These are the so-called micelles, by the way. More on this further down in the article.
This is how a cream is created. There are oil-in-water emulsifiers and also water-in-oil emulsifiers. If you want, I can write a separate post about this. Let me know what interests you!
Yes, and because surfactants are so good at mixing, they are also considered to be excellent cleaners. They help the water to remove fat-soluble dirt and make-up from our faces. Of course, they do this in the kitchen, the washing machine, and so on. Just like argan oil, in this case they trap dirt particles and distribute them in the washing water. Pretty cool, I think.
# 3 Surfactants differ mainly by their water-loving “head”
Fig. 3
As you can see in my figure 3, the hydrophilic ends partly carry electrical charges and partly do not. These charges determine how well the surfactant dissolves in water, what pH value the surfactant brings with it and thus how it works. This charge also determines how strong and therefore how aggressive a surfactant is for our skin and the environment!
There are
- anionic surfactants
- cationic surfactants
- amphoteric surfactants
- neutral/non-ionic surfactants
In order not to beat around the bush, I have prepared a few graphics and drawings for you. I hope they are understandable for you and help you to better understand the characteristics of our little elves.
Anionic surfactants
Fig. 3.1
The negatively charged surfactants have the highest cleaning power and are found in many foaming cleaning agents and gels. A very common example is sodium laureth sulfate! In Fig. 3.1 you can see how the name is composed.
Sulfates are among the most aggressive surfactants. They don't stop at your skin's fats and attack your acid mantle. They open the door to germs and unwanted foreign bodies. As a result, they are suspected of causing allergies, dry skin, brittle hair and flaky scalp. (3)
NOTE: You can usually recognize anionic surfactants by the term “sodium” (the counter ion for the negative charge) and “sulfate” surfactants tend to be avoided.
Of course, there are also non-ionic surfactants, such as disodium cocoyl glutamate, which is a little milder and therefore better tolerated. It all depends on the cleaning power you want from a product. The important thing is that you are aware of what you are dealing with. The decision is ultimately yours!
But what I'm wondering at this point is: does our skin need such a strong cleansing? After all, healthy skin has good self-regulation. It is an autonomous organ. We want to do everything we can to ensure that the skin can carry out its tasks and, above all, its abilities without hindrance.
Of course, external influences change and our lifestyle often leaves its mark. This makes it all the more important to avoid irritating substances as much as possible and to take the health of your skin seriously.
Speaking of health, the health of our environment also plays a major role, especially in connection with the topic of surfactants. More on this later.
The soap
The anionic surfactants also include normal soap surfactants. They are created when fats, such as coconut oil, are broken down using lye. The process, which is also called saponification, creates a potassium or sodium salt of the original fatty acid.
Soaps are not ideal for our skin. They cause the skin to swell and attack the acid mantle. This is also due to the relatively high pH value of 7-8. (3)
However, a high level of washing power may be required, especially when washing hands, and so people often resort to the tried and tested soap. Apart from that, it is also easily biodegradable.
Cationic surfactants
Fig. 3.2
Ammonium compounds are preferred here to maintain the positive charge of the cationic surfactants. The counterion is often the chloride anion. Since cationic surfactants are not used as washing ingredients, but rather in hair shampoos and conditioners to ensure that the hair does not fly away after washing, I will neglect them a little here.
Cetrimonium Chloride would be an example INCI. (2)
Neutral/non-ionic surfactants
Fig. 3.3
As their name suggests, neutral surfactants do not carry any charge. This makes them very mild and skin-friendly. They also hardly foam. They include a number of very chemical-sounding surfactants.
Fatty acid ethanolamides, fatty alcohol ethoxylates, macrogol fatty acid esters (PEG) and alkyl polyglycosides.
The alkyl polyglycosides are my favorites. They are also called sugar surfactants because their hydrophilic head consists of a sugar molecule. They have almost no effect on the skin barrier and also greatly reduce the irritation potential of other surfactants. They improve the dry combability of the hair, its bounce and its tear resistance. Top surfactants!
You can often recognize them by the root word “glucoside” or “sucrose”.
Amphoteric surfactants
Fig. 3.4
This group of surfactants combines the positive properties of anionic and neutral surfactants. They are mild, but still have good cleaning power and even a very acceptable foaming performance! They are also easily biodegradable. (2)
You can recognize them by the root words “betaine” and “-ampho-”!
Betaines owe their name to betaine, a substance that is very similar in structure to them and comes from sugar beet (Beta vulgaris). They are often used in combination with anionic surfactants to reduce their irritating potential while maintaining good cleaning power.
Now you are at least well-equipped with basic knowledge of surfactants. You can find out more information about what micelles are all about and how you can clean your skin gently but effectively in the next blog post!
Take time for yourself & be good to yourself!
Your Leonie
Sources
- Cosmetic ingredients from A to Z, Heinz Knieriemen, 6th edition, 2005, AT Verlag Baden and Munich
- Personal care and cosmetics, Sabine Ellsässer, 2nd edition
- Guide through the world of cosmetics, Esther Witte, 2nd edition, 2019