Sodium Lauryl Sulfate (SLS)

What is SLS and what does it do?

Sodium lauryl sulfate is an anionic surfactant made by sulfating a fatty alcohol obtained from coconut or palm kernel oil. One end of the molecule is attracted to water and the other to oil; this allows it to make dirt and grease washable with water.

In products it does three main jobs: cleaning, foaming and helping other ingredients to mix. Because it is cheap and very effective, it has been one of the most widely used foaming agents for decades.

Which products contain it?

• Shampoos, shower gels, liquid soaps and face washes
• Toothpastes (to create foam in the mouth)
• Washing-up liquids, surface cleaners and some laundry detergents
• Bubble baths and shaving foams

On the label it usually appears right after water (Aqua), that is, among the ingredients present in the highest amounts.

Is it harmful? The scientific assessment

The independent Cosmetic Ingredient Review (CIR) panel has stated that SLS is safe in rinse-off products, while in products that stay on the skin for a long time its concentration should not exceed 1%. The reason is not toxicity, but that at high concentrations and with prolonged contact it can dry out and irritate the skin barrier.

The claim often circulating online that "SLS causes cancer" is not true: SLS is classified as a carcinogen neither by the IARC nor by the EU. This claim largely stems from confusion with the 1,4-dioxane residue that can form during the manufacture of SLES; this residue is not an issue with SLS.

In cleaning products, pure SLS is classified as irritating to the eyes and skin; however, in products it is present in diluted form and has only brief contact.

Who should be careful?

• People with atopic dermatitis (eczema) or very dry skin: SLS can increase dryness and itching by dissolving the lipids in the skin barrier.
• People who often get mouth ulcers (canker sores): Some studies have shown that SLS-free toothpastes can reduce how often mouth ulcers occur.
• People with coloured or very dry hair: Its strong cleansing effect can make hair feel drier.
• Eye contact: It stings if it gets into the eyes; rinsing with plenty of water is enough.

The difference between SLS and SLES

SLES (Sodium Laureth Sulfate) is the ethoxylated form of SLS. This process makes the molecule larger and milder on the skin; that is why SLES is assessed with a lower risk range in the app. On the other hand, SLES may contain trace amounts of 1,4-dioxane left over from manufacturing; reputable manufacturers minimise this through purification.

What to do when you see it on a label

If your skin has no problems, there is no reason to stop using a rinse-off product containing SLS. If you have sensitive skin, eczema or frequent mouth ulcers, you can try "sulfate-free" products made with milder surfactants such as coco glucoside, decyl glucoside or cocamidopropyl betaine. Wearing gloves while cleaning largely prevents the irritating effect of all detergents, including SLS.