Is SLS bad? What “sulphate-free” does and doesn’t mean

Short answer: SLS isn’t a poison, but it is a real irritant, and how much it bothers you depends on dose and contact time. A quick rinse-off wash suits many people and not others. “Sulphate-free” only tells you one ingredient family is missing. It says nothing about what replaced it.

Search “SLS” and you get two confident answers. It’s a toxin. It’s perfectly safe.

Both are partly right. Neither helps you pick a cleanser.

What is SLS, and why is everyone fighting about it?

Sodium lauryl sulphate is strong, cheap and lathers beautifully. A 2022 review in Molecules calls it a strong, conventional anionic surfactant. Anionics as a family give the most cleansing power and excellent lather, and the same review says they’re “considered potent irritants to the skin.” One trait, two reputations. The pull that lifts oil off so well is also the thing that can bother skin.

SLES, its ethoxylated cousin, is generally considered milder. Still a sulphate.

Is it actually irritating?

Yes, and dermatologists count on it. For about two decades, German patch-test series have included a 0.25% SLS solution as an irritant control. A 2026 analysis in Contact Dermatitis covered 43,478 patients, and 22.4% reacted. Most of those reactions were weak, so roughly 78% had no reaction at all. The authors call it “not a universal marker” of how irritable someone’s skin is. So yes, at that strength it irritates some people some of the time. That’s the whole point of a control.

Hold onto one detail. A patch keeps that solution against skin for a long stretch. Your wash is a minute of contact, then a rinse.

Does dose and contact time change things?

Hugely. The Cosmetic Ingredient Review panel, an expert group funded by the cosmetics industry (worth knowing), found SLS appears safe for brief use followed by thorough rinsing. For products that stay on skin, it recommended keeping it at or below 1%. For SLES the wording is blunter: irritation rises with concentration, and these ingredients should be used only when they can be formulated to be non-irritating.

Notice the word that never appears. Never.

The panel’s position is that it depends how the product is built and how long it sits. Less exciting than “toxic”, which is probably why you don’t see it on a viral post.

What about cancer, and the toothpaste scare?

Cancer first. The Cosmetic Ingredient Review assessment reports that SLS was not carcinogenic in experimental animals. Its established concern is irritation.

SLS turns up in toothpaste too, because it foams well, doesn’t change the taste and costs little. Whether it contributes to mouth ulcers is still argued over. A mid-1990s study found more ulcers with SLS toothpaste, while a later trial found no significant difference in ulcer frequency. Decades in people’s mouths and the evidence is still mixed, so one word on a face wash was never going to settle your skin.

So does “sulphate-free” mean mild?

No. It means one suspect is off the list.

Soap has no sulphate in it, and the Molecules review calls it harsher on skin than syndet cleansers. Plenty of strong surfactants aren’t sulphates either. Dermatologist Leslie Baumann, writing on a site that sells cleansers, calls sodium C14-16 olefin sulphonate a strong anionic, though it’s a sulphonate.

Then there’s the usual helper in sulphate-free washes, cocamidopropyl betaine. In that same German patch-test data, people who reacted to SLS also tended to react to a handful of other strong irritants. It was one of them.

What actually makes a wash mild?

The whole system, not a single name.

The Molecules review notes that adding amphoteric and nonionic surfactants can lower the irritancy of anionic ones, so a surfactant inside a well-built blend isn’t the same thing as that surfactant alone. Nonionics are usually the gentlest class, though too much can dissolve more skin lipids, and in one electron-microscopy study it describes, an isethionate disturbed skin lipids less than a nonionic cleanser did. Concentration and time on skin do the rest.

Then there’s your own skin, which is stubbornly hard to predict. A 2020 British Journal of Dermatology study patch tested 2,030 patients with 0.25% SLS. About 14.2% of people with signs of an atopic tendency, the eczema-and-allergy kind of skin, reacted, against 16.8% of those without. No significant difference. “Sensitive” is a rough guide at best. A patch test on your own jaw says more.

What should you ask instead?

Three quick things. What leads? The first cleansing ingredient after water tells you what you’re dealing with. Is it alone, or are milder partners behind it? And how does your skin feel after a week, not an hour, of the same wash with nothing else changed?

Here’s how the first two look on a real label. Say a list reads water, a sulphate, then cocamidopropyl betaine: a sulphate leading, with a helper behind it. Another reads water, sodium cocoyl isethionate, then a betaine: a different lead, same kind of helper. Neither tells you the amounts. Both tell you more than the front of the tube.

And if your current wash has SLS in it and your skin has been happy for months, nothing here says you have to switch. If it stings, or skin feels rough by day three, that’s information too. Either way the test is your own week, not the word.

If you have eczema or another diagnosed condition, treat this post as a list of questions, not answers. A dermatologist who can see your skin and your actual products will beat a blog every time, this one included. Washing every day isn’t a patch test, and a patch test isn’t a forecast for your face.

What does it look like in real life?

Picture someone (an illustrative example, not a testimonial) who bins every SLS product after a viral post and buys a “sulphate-free” wash. Her face still stings.

She turns the tube over. The lead cleanser is another strong surfactant with nothing obvious behind it. Nothing on pH. Nothing on how it was blended. The front said sulphate-free and that was the end of the information.

So she patch tests a wash with a different lead ingredient, uses only that for a week and watches. Maybe the stinging eases. Maybe it doesn’t, which is useful too. Either way, she’s judging her own face now, not a word.

Where does Mugtea fit?

Mugtea is designed with all of that in mind. Its lead cleansing ingredient is SCI, sodium cocoyl isethionate, which isn’t a sulphate. It’s a blend: SCI leads, a gentler co-surfactant supports, and glycerin and panthenol look after how skin feels afterwards. It’s designed with normal, oily and combination skin in mind, and it goes from paste to cream to foam as you work it.

Mugtea contains no SLS or SLES anywhere, and you can read every ingredient on the product page. Cleanser, supporting blend and every ingredient are listed, because that tells you more than any one word could.

Mugtea is a cleanser, not a treatment. It also contains salicylic acid, so patch test on your jawline first, use only the daily wash for a week and stop if your skin objects. Reactive skin, or on prescription treatment? Ask a dermatologist before you start.

Mugtea is launching soon. Meet Mugtea →

Turn over the wash you’re using right now. What does it lead with, and what’s behind it? Tell us. We’ll explain the answers in a future post.