Sulfate-free shampoo: what the label means, what counts, and the cousins that slip through

Sulfate-free is the most common promise on a shampoo bottle after moisturising. It is also one of the few claims you can check yourself in ten seconds, if you know the names.

What a sulfate is

In shampoo, a sulfate is a cleansing agent, a surfactant, that grabs oil and rinses it away with a lot of foam. The big three are Sodium Lauryl Sulfate (SLS), Sodium Laureth Sulfate (SLES) and Ammonium Lauryl Sulfate (ALS). Close relatives with the same job: Sodium Coco-Sulfate, Sodium Myreth Sulfate, Sodium C12-13 Pareth Sulfate, Sodium Cetearyl Sulfate.

They are effective and cheap, which is why they sit second on so many lists, right after water. Effective is also the complaint: on dry, curly or colour-treated hair, and on some scalps, a strong sulfate can strip too much.

What is not a sulfate

Several ingredients contain the letters sulf and are not the cleansing sulfates people mean:

• Magnesium Sulfate is Epsom salt, used for texture.
• Sodium C14-16 Olefin Sulfonate is a sulfonate. It is a strong cleanser too, and some people who avoid sulfates avoid it as well, but chemically it is a different group.
• Behentrimonium Methosulfate is a conditioning agent, not a cleanser at all.
• Disodium Laureth Sulfosuccinate and Sodium Lauryl Sulfoacetate are the milder alternatives brands reach for when they go sulfate-free.
• Sodium Metabisulfite and Sodium Sulfite are antioxidants.

If a checker counts all of these, most sulfate-free shampoos would fail. Ours does not count them.

Why a sulfate-free bottle still foams

Foam comes from surfactants, not from sulfates specifically. Sulfate-free formulas use glucosides (Coco-Glucoside, Decyl Glucoside), Cocamidopropyl Betaine, Sodium Cocoyl Isethionate or sarcosinates. They lather a little less richly, and rinse a little differently, but they clean.

How we check

The sulfate-free check looks for the cleansing sulfates and their spellings, including the one-word forms and typos that turn up on packs. Mineral sulfates, sulfonates, methosulfates and sulfosuccinates are left out on purpose, and the page tells you when a sulfonate is present so you can decide for yourself. If the label says SLS-free but the list shows Ammonium Lauryl Sulfate, the answer is still no: ALS is a sulfate, whatever the front says.

Reading the bottle

Find the second or third ingredient. If it ends in sulfate and starts with sodium, ammonium or magnesium-laureth, you have a sulfate shampoo. If it ends in glucoside, betaine, isethionate or sarcosinate, you are looking at a sulfate-free one.