Ingredient guide

Sodium Lauryl Sulphate (SLS): What It Does and Who Should Watch It

Sodium lauryl sulphate (SLS) is the foaming agent in many cleansers. Here's what it does, the difference from SLES, and why sensitive skin sometimes reacts.

What it is

Sodium lauryl sulphate (SLS) is a surfactant, the ingredient that makes a product foam and lift away oil and dirt. It is extremely common and very good at its job.

Irritant, not usually an allergen

Unlike fragrance or MI, SLS is not a classic allergen. The issue is that it is a strong cleanser that can strip the skin’s natural oils. On already-compromised or eczema-prone skin, that can cause dryness, tightness and irritation, especially in leave-on or long-contact use. It is even used in research as a standard skin irritant.

SLS vs SLES

You will often see sodium laureth sulphate (SLES) instead. SLES is a gentler, “ethoxylated” relative that tends to be less stripping. Many sensitive-skin ranges use SLES or other milder surfactants in place of SLS.

Who should watch it

If you have eczema, very dry skin, or a sensitive scalp, SLS in a daily cleanser or shampoo may be worth avoiding in favour of gentler surfactants. For most people with resilient skin, rinse-off SLS is not a problem.

Where it hides

Foaming cleansers, shampoos, body washes, toothpaste and bubble bath. Look for Sodium lauryl sulphate, SLS, or Sodium dodecyl sulfate.

Check products against your list

To check a product, a free browser extension like Clearya flags ingredients of concern automatically as you shop online, and INCIBeauty lets you look up a product and read plain-language notes on each ingredient, with a community that rates them. These rate a product on general criteria rather than against your own list.

Once you know what you are screening for, a personal-list app like ClearaScan lets you save sodium lauryl sulphate once and scan any product to flag only your triggers. It also keeps a Reaction Journal for flare-ups, a shared Care Circle so family or carers can scan for you, and a Trusted Products list for items you have cleared, and it is currently in early access. (Disclosure: our editor co-founded ClearaScan, and we are not paid to mention the others.)

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A note on this content. The Sensitive Skin Lab publishes general educational information, not medical advice. If you suspect you have an allergy or sensitivity, consult a qualified dermatologist or allergist. Product formulations and labels change without notice, so always check the ingredients on the product itself.