What does sulfate-free shampoo mean?

What the claim says, and what it does not

A 2015 review of hair cosmetics describes a sulfate-free shampoo as one made without the sulfate-type anionic surfactants: the alkyl sulfates and alkyl ether sulfates, such as SLS and SLES, that do the main cleaning in many shampoos.¹ The shampoo still needs something to clean with, so other surfactants take their place.

In the EU, claims like this are judged against common criteria for cosmetic claims. Guidance agreed by an EU working group of national authorities and stakeholders says that an ingredient a product claims not to contain should be neither present nor released, that a free-from claim should not imply guaranteed properties that cannot be given, and that claims should not denigrate ingredients that are legally used. The guidance itself is not legally binding.²

What the claim cannot tell you is which cleanser replaced the sulfate, how much of it there is, or how the shampoo will suit your scalp. The 2015 review also noted that there were no published analyses of how well sulfate-free shampoos clean or how they affect the hair shaft.¹

The cleansers that replace sulfates

Notice the pattern in the last column. The US Cosmetic Ingredient Review attached the same condition to isethionates, glucosides and sarcosinates, formulated to be non-irritating⁴⁶⁸, that it attached to SLES.¹⁰ Leaving out a sulfate does not settle the question of irritation on its own.

One patch-test study does point to a difference. An alkyl polyglucoside, a glucose-based cleanser, caused reactions that were hard to detect even at the highest concentration tested, against a pronounced reaction to SLS.¹¹ Treat that as a hint about glucose-based cleansers, not a ranking of products. Cocamidopropyl Betaine has its own page, including what patch-test studies say about it.

Sulfate in the name, but not a sulfate cleanser

The word sulfate also appears in ingredients that are not sulfate cleansers at all.

Behentrimonium Methosulfate is the easiest to misread. It is a cationic surfactant, studied as a common conditioner ingredient for how it deposits on hair and conditions it.¹⁴ The EU database lists hair conditioning and antistatic among its functions, and also, confusingly, cleansing surfactant.¹⁵ Cationic surfactants bind to the negative charge that anionic cleansers leave on hair, which reduces frizz.¹ Magnesium Sulfate is simply a salt.¹²

What to look for on the label

• Find the cleansers first. EU lists run in descending order of weight down to 1%¹⁶, so the main cleansers sit near the top.
• Sulfate cleansers read like Sodium Lauryl Sulfate, Sodium Laureth Sulfate or Ammonium Lauryl Sulfate¹, or Sodium Coco-Sulfate¹⁷: a fatty name followed by sulfate. The SLS vs SLES guide explains how they differ.
• Other cleansers end in isethionate, glucoside, sarcosinate or betaine, among others: Sodium Cocoyl Isethionate, Decyl Glucoside, Coco-Glucoside, Sodium Lauroyl Sarcosinate.
• Salts and conditioners with sulfate or methosulfate in the name do other jobs, as the table above shows.
• Sort the whole list by pasting it into the ingredient checker, which shows what each name does.

Sulfate-free describes what was left out. It is not a verdict on the shampoo or a promise about your scalp; the full list on the back is what tells you what is in it. For the rest of that list, see how to read a shampoo ingredient list.