Shampoo surfactant types: the four families on a label

Four families, sorted by charge

A surfactant has one end drawn to oil and one drawn to water: the first binds to sebum and dirt, the second lets water rinse them away.¹ The EU database describes a cleansing surfactant's job as wetting the surface, emulsifying or dissolving oils, and holding dirt in suspension.² By the electric charge on their water-loving end, surfactants fall into four families: anionic, cationic, amphoteric and non-ionic.³

No label prints the family. The name is the only clue, and the last section shows how to read it.

Anionic: the main cleansers

Anionic surfactants are the most popular in shampoos and remove sebum from scalp and hair very effectively.¹ That strength has a cost: they can add negative charge to the hair surface and increase frizz and friction, which is why other surfactants are added beside them.³

They come in several classes. Lauryl sulfates work in hard and soft water, foam richly and rinse easily. Laureth sulfates are common primary cleansers in shampoos for normal to dry hair. Sarcosinates remove sebum less well and usually come second or third among the cleansers.¹ Isethionates and sarcosinates are anionic too⁴, so a shampoo with no sulfate can still clean with an anionic surfactant. What sulfate-free means covers those replacements, and SLS vs SLES the two best-known sulfates.

Amphoteric: the usual second cleanser

Amphoteric surfactants carry both a negative and a positive group, so they behave like cationic surfactants at lower pH and like anionic ones at higher pH.¹ Cocamidopropyl Betaine is a zwitterion used mainly as a surfactant⁵, and a 1997 review described it as long the most important secondary surfactant in personal cleansing products.⁶ Imidazoline-derived amphoterics such as Sodium Cocoamphoacetate play a smaller role.⁶

Their reputation is mildness. One review calls the family very mild³; another notes that amphoterics such as the betaines are used in baby shampoos, and in shampoos for fine and chemically treated hair because they foam moderately well and leave hair manageable.¹ Mild is not the same as never reacting: the Cocamidopropyl Betaine page covers what patch-test studies found.

Non-ionic: no charge, the mildest

Non-ionic surfactants carry no charge. They are among the mildest cleansers, and shampoos pair them with ionic surfactants as a secondary cleanser.¹ The glucosides belong here: alkyl glucosides such as Decyl Glucoside, Lauryl Glucoside and Coco-Glucoside are non-ionic surfactants made by reacting glucose with fatty alcohols⁷, and their use in personal care products has been growing.¹¹

The alkanolamides are another non-ionic group.¹ Cocamide MEA, a mixture of ethanolamides of coconut acid, is listed in the EU database as a foam booster and viscosity controller.⁸ Foam spreads shampoo over hair and scalp, but it does not do the cleaning.¹

Cationic: conditioning rather than cleaning

Cationic surfactants carry a positive charge. They clean poorly, lather little and do not combine well with anionic detergents¹, but they bind to the negatively charged hair surface, neutralise it and reduce frizz.³ That makes them the backbone of conditioners¹⁰, as the conditioner ingredients guide explains, along with the EU limits on Behentrimonium Chloride and Cetrimonium Chloride: Annex III, entries 287 and 286, when they condition, and Annex V, entry 44, up to 0.1%, when they preserve.¹²

Shampoos built on anionic cleansers can carry the positive charge in cationic polymers instead. In tests on shampoos made with sodium laureth sulfate, polymers including Polyquaternium-10 and cationic guar gum all improved performance, judged by combing force and the feel of the hair.⁹ With anionic surfactants, cationic guar forms complexes, called coacervates, that deposit on the hair.⁴ On a label they read as Polyquaternium-10 and Guar Hydroxypropyltrimonium Chloride, both listed by the EU database as antistatic and film forming.¹³¹⁴

The same cling has a downside. Cationic polymers can hold on to hair so well that they are difficult to remove³, and in the shampoo tests, poor removability and build-up were the most striking weaknesses of the cationic guar polymers.⁹

Why shampoos combine them

A shampoo has 10 to 30 ingredients. Because its cleansing depends on the type and amount of surfactant, it is a blend chosen for the hair it is meant for.¹⁵ Modern shampoos usually contain two to four surfactants: the first listed is the primary cleanser, at the highest concentration, and the next is a secondary cleanser chosen to offset its shortcomings.¹⁰

Surfactants also do more than clean. A review of shampoo surfactant technology lists foaming, controlling how the shampoo flows and thickens, mildness to skin, and depositing conditioning agents on hair and scalp among their jobs.¹⁶ Another stresses that how the ingredients interact matters more than any one of them alone.³ A label gives no amounts, so it shows which families are present, not how strong the blend is.

Reading the family from a label

• Anionic names often end in sulfate, sulfonate, sarcosinate, sulfosuccinate or isethionate.³¹⁴ Not every name ending in sulfate is a cleanser: what sulfate-free means lists the exceptions.
• Amphoteric names include betaine, sultaine and amphoacetate, as in Cocamidopropyl Betaine or Sodium Cocoamphoacetate.¹⁶
• Non-ionic cleansers include names ending in glucoside, and alkanolamides such as Cocamide MEA.⁷¹
• Cationic names often contain trimonium or quaternium: these are quaternary ammonium compounds, or quats.³¹⁷¹³
• Order helps. In the EU, ingredients above 1% are listed in descending order of weight¹⁸, so the first surfactant after water is normally the primary cleanser.¹⁰
• Check a whole list in the shampoo ingredient checker, which shows each name's role.

A surfactant's family is not a verdict on a shampoo. How mild a shampoo is depends on the blend and the amounts, which no label gives. For the rest of the list, see how to read a shampoo ingredient list.