Ep 18: Not Sulfate Free? Not a Problem! Surfactant Chemistry Will Teach You Why.

A couple weeks ago I told you all about Emulsifiers, and how they are the secret ingredient to hold oil and water together to create emulsions. Or things like creams, conditioners, lotions, milk mayo etc. Well today, we are going to back it up a little bit and talk about an even broader term - surfactants. 

It is officially the new year. And new year = new me. Jk. but a lot of people are making new goals and trying to create new habits. I felt like there was no better way to wash away 2025, than to talk about surfactants. 

So what is a surfactant? And how is it going to wash anything away? 

Surfactant is a very fun concept for a word - it is a truncated version of the words Surface Active Agent. So it is a material, or active, that changes (lowers) the surface tension of a liquid. We will review surface tension, but first I want to talk about this word concept more. 

What's a surfactant?

Surfactant stands for surface active agent 

I feel like we could do more like this: 

Thiniliketave- Things I like to Have 

Alitsomswet-  A little something sweet 

Coffeeanddillydally- Running a few errands 

So now back to figuring out what a surfactant actually is lets review surface tension. I know its been a while, its a whole new year. So surface tension is the measurement of how strongly the molecules of a liquid are held together. We all know the three phases of matter, solid liquid and gas. Solids are made up of molecules that are strongly connected to one another. So much so that you cant pass though them. Liquids are less strongly held together. You can pass through them. Gasses have the least amount of attraction between molecules. 

You can also think of it like a room with a bunch of people in it. If the room is packed with people, shoulder to shoulder, its going to be very difficult for anyone to walk about in there (solid) if there are a dozen people in the room you can walk through, but people may need to move around a bit. If there is only one other person, you can probably move quite freely. In this example, the molecules (or people) are being held together by pressure. 

For states of matter, they are held together by magnetic forces. We talk about it quite frequently on this podcast, but my friend atom is made of three parts. A neutral, a positive, and a negative. Depending on the balance, atom can either be positive or negatively charged. This charge in atoms determines how they are going to react with other atoms they are around. 

Atoms are very very very small. So individually we can not see them. That is why we cant really see gases. The atoms that make up that gas do not have strong magnetic forces pulling them together. So they are just individually floating around in space. 

If the attraction between those molecules increases, then they will start to form groups, and eventually, once that group is big enough we will be able to see it.

A great example of this is water, because as we know, there is water in the air. Sadie talked about it more recently on the winter hair and skin care episode. But the air contains water, which we refer to as humidity. The reason we cant see the water in the air is because the individual molecules are too far apart from each other. But when the temperature of the air decreases, the attraction between the water molecules increases, and they start to form groups. Eventually, these groups get so big, that they get too heavy to stay up in the air, and they fall down (rain).

Basically all that review is just to remind you that surface tension is the measurement of how strongly the individual molecules in a liquid are bound to each other. 

In cosmetics surfactants are typically ingredients that decrease the surface tension of water molecules. Water is polar, meaning it has a positive charged end and a negatively charged end. These charges mean that when a bunch of water molecules are together, they form a pretty uniform structure. 

This gives water a very high surface tension. Even at room temperature. 

We talked about the chemistry behind this a lot in the emulsifier episode, because emulsifiers are a type of surfactant. We talked about how in order to form an emulsion, we need to be able to over come the surface tension of water. 

Water likes to mix with other highly charged things, or other polar things. We have said this a million times already but like dissolves like. So water will dissolve other charged things like salts and ethanol (alcohol). Because you are just adding more magnets to your magnet soup. These things combine to form your water phase, or hydrophilic phase.

Non charged liquids typically fall into the oil category. Or lipophilic. These work a bit more like velcro in their attraction. One of those little loops doesn't hold very strong, but the whole strip has some stick. 

Emulsifiers or surfactants are the socially liberally fiscally conservatives. 

Let's talk about ions

We have been talking a lot about charged things. But what do we mean by that? So if you have played with magnets, I will remind you that there is usually a positive and negative end of the magnet, and the opposite sides attract. Sometimes it is also a north pole and a south pole in a magnet (Because they are Polar). 

When we talk about magnets we often talk about the poles, N and S because that is how they work. A compass is just a magnet. That is why no matter what direction you turn it, the ‘south’ end of the compass is always going to point north. Because those poles are attracted to each other. 

In chemistry, and with atoms and molecules we use different terms, but the concepts are similar. If a molecule becomes ‘charged’ we call it an Ion. Then we can more specifically say if its a positive or negative charge by calling it either Cationic or Anionic. 

I have always remembered these because cat-ionic. Cats make me happy. Anionic sounds like onion. Onions make me cry. Maybe that will stick for some of you. If not, you might not need to remember it for your adult life purposes. 

But surfactants are used for much more than just emulsification.

Surfactants are a very broad category of ingredients. But just like emulsifiers, surfactants have a water loving part, and an oil loving part. Which allows them to stick to both categories of ingredient. 

We touched very briefly on their potential when we mentioned Micellar water. But typically when we talk about surfactants in cosmetics, we are talking about cleansing. So this is stuff like shampoo, body wash, hand soap, face wash, surface cleaner, dish soap, etc. 

When I say they are a broad category, I mean that even though in seems simple enough. Water loving side, oil loving side. These molecules can have vastly different properties, depending on the atoms they are made out of. 

We have talked a lot about how water molecules have a partial charge, or are polar. And because we know like dissolves like, it might make some sense for the water loving part of the surfactant molecule to have some charge as well. 

We have 4 main types of surfactants, that can be classified based on the type of charge that the water loving head of the molecule has. 

Can you guess what each of these means now based on our review? 

• Non-ionic means that there isn't a charge. 

• Cationic- Means it carries a positive charge

• Anionic - Negative charge

• Amphoteric or Zwitterionic, means that it can carry either positive or negative, depending on the the situation its in. 

So if we are trying to make sense of non ionic vs amphoteric, is sorta like in an argument non ionic doesn't make their opinion known. Amphoteric just agrees with the majority. 

I want to give you a brief description of how each of these are different, but I don't want to bore you with the scientific details, since as a consumer… they might not matter that much. And I will tell you why. 

But I also think knowing the types can be helpful to understand the differences. 

The order we are going to talk about them in is also going to sorta kind of go against the order I would naturally want to.  For me i want to do like not charged, positive, negative, both. BUT 

Anionic and Cationic are not compatible. DO NOT MIX. So to talk about them in this order doesn't really make sense. 

Cationics are compatible with Amphoteric and Non-Ionic

Anionics are compatible with Amphoteric and Non-Ionic

Cationic and Anionic do not go together in the same system. We can talk more about its relevance in hair care. 

We are going to start with Anionic, because these are the ones that probably carry the ‘surfactant’ name the strongest in the cosmetic world. 

Anionic - Creates a negative head group in water. These are your ‘primary’ surfactants. They are used to lift and suspend oils, but they don't necessarily dissolve them. In this category are sulfates. These are really good at removing particulate soils like calcium buildup. 

Anionic surfactants also create a lot of foam.

Non-Ionic - A lot of Ethoxalates, aka PEGs. We talked about HLB value in the emulsifier episode. The properties of Non-Ionic emulsifiers can vary drastically depending on the HLB value, and whether its more attracted to Oil or Water. But in general, non-ionic surfactants are good at solubilizing oils. 

Amphoteric/Zwitterionic - pH changes depending on the pH. Tend to offer more gentle cleansing. Offer more versatility to systems because you can then have the properties of cationic conditioning in anionic systems. 

• Coco Betaine – These are used in personal care products like shampoos and Laundry detergent. Polyventive is a leading manufacturer for various alkylbetaine derivatives.

• Hydroxysultaine – Common in Conditioners, cosmetics, and industrial cleaners. Amphoterics offered by Polyventive include cocamidopropyl hydroxysultaine.

• Cocoamphodiacetate – Used in hair and skin conditioning products. Polyventive manufactures cocoamphodiacetate imidazolines.

• Lauroamphoacetate and Amphoglycinates – Sodium Caprylamphoacetate is used in shampoos and bubble baths.

• Sarcosinates – These are used to improve Foam Boosting and quality in shampoos.

• Sultaines – Offer Foam Stabilizing and good conditioning in personal care products.

Biblography

1. Polyventive. (2025, December 10). Amphoteric surfactants. Polyventive. Retrieved January 16, 2026, from https://polyventive.com/surfactants/amphoteric-surfactants/ 

2. Mannina, D. (2020, April 15). FIU@Home: Discover why water matters. FIU College of Arts, Sciences & Education (CASE). Retrieved January 16, 2026, from https://case.fiu.edu/education-outreach/fiuhome/discover/kitchen-science/2020/discover-why-water-matters.html