Cationic vs anionic cosmetic ingredients – what should be used in your formula? 

Anionic surfactants

The first thing we need to cover is the use of the term ‘surfactants’ as it applies to cosmetic formulation. A surfactant is any substance with a water loving end and an oil loving end that enables two normally immiscible phases – oil and water – to mix.

When it comes to cosmetic formulation, however, we tend to call anionic surfactants that cause bubbles and foam exactly what they are: anionic surfactants. This includes materials like sodium lauryl sulfate, sodium lauryl sarcosinate, sodium cocoyl isethionate and so on. Anionic surfactants tend to have a very strong clean because of their negative charge, so are commonly also referred to as primary surfactants in cosmetic formulas.

There is another very important type of anionic surfactant that we use regularly in cosmetic formulas, and that is the one that helps us form creamy emulsions. Where an anionic ‘surfactant’ helps us form a cream instead of bubbles, we call it an anionic emulsifier. Chemically, it is still a surfactant, but when formulating cosmetics, these materials are called anionic emulsifiers. Common examples include stearic acid, sodium stearoyl glutamate, sodium stearoyl lactylate and so forth. Anionic emulsifiers will have a strong stabilising effect on an emulsion because their charge helps with electrostatic stabilisation – keeping micellar droplets of oils away from each other based on a charge repulsion effect.

Anionic surfactants can be irritating to the skin unless combined with other non-ionic or amphoteric surfactants or polymers, as suited to different formulation types.

Learn more about the difference of surfactants with this video.

Cationic surfactants

Cationic surfactants are also subject to the same type of terminology as anionic surfactants, however because these materials typically only create emulsions (most commonly conditioners), they are most often referred to as cationic emulsifiers.

Cationic emulsifiers/surfactants always give a slippery feel to the skin or hair, and that is because their positive charge clings tightly to the (normally) negatively charged skin and hair. They are particularly great at detangling hair and giving it a nice conditioned feeling. You are probably familiar with names like cetrimonium chloride, behentrimonium chloride, and behentrimonium methosulfate. Watch how to make a conditioner here.

Like anionic surfactants/emulsifiers, cationic emulsifiers can be irritating to the skin unless they are combined with non-ionic emulsifiers. They should not be used on their own for this reason, and some cationic emulsifiers have regulatory restrictions placed on their use to limit potential irritancy.

Cationic surfactants/emulsifiers are NOT compatible with anionic surfactants/emulsifiers – if you use the two together in a cosmetic formula, you will get an insoluble complex form.
 

Cationic polymers

Now, this is where the confusion comes in: there is another class of cosmetic chemicals we need to talk about that get used extensively in anionic foaming formulas… the cationic polymer.

Cationic polymers are NOT the same as a cationic surfactant/emulsifier.

Cationic polymers carry a positive charge but have nowhere near the same amount of polarity or electrostatic charge as a cationic surfactant/emulsifier. Cationic polymers are a polymeric material with cationic charge, such as guar hydroxypropyltrimonium chloride, or polyquaternium-7. These are both polymers with a repeating backbone that have cationic molecules attached along their chain.

Compare this to a surfactant material, however, which is completely hydrophilic at one end vs hydrophobic at the other and sets up electronegativity in the molecule.

This means you can create cosmetic formulas with anionic surfactants/emulsifiers with cationic polymers present. In fact, the combination of these materials is very common and leads to very effective skin or hair softening results.

You can of course use cationic polymers in formulas containing cationic surfactants/emulsifiers for even better results.

Cationic polymers ARE compatible with both anionic and cationic emulsifiers/surfactants.
 

Make sure you check the cationic material you want to use before formulating!

When formulating with anionic surfactants/emulsifiers, it is often recommended to use a non-ionic emulsifier/surfactant/solubiliser or even superfatting agent, depending on the type of formula you want to create. We have so many videos on hair formulas, they have their own playlist! Watch here…

Cationic polymers are also a great addition to your wash off anionic surfactant formulas, and are completely compatible and even boost final conditioning and softening performance!

Just remember to identify carefully it is a cationic emulsifier or surfactant – these should be used with non-ionic surfactants/emulsifiers only, and combine well with cationic polymers.

Hopefully this helps clarify one of the biggest confusion points for those new to learning cosmetic science and cosmetic formulation: when cationic and anionic cosmetic ingredients can be combined, and when they most certainly cannot.


Happy formulating!