Last updated: June 2026 · The Earthling Co.
If you’ve ever flipped a shampoo bottle over and tried to decode the ingredient list, you’ve probably run into SLS, SLES, and SCI. They’re all surfactants — the workhorse ingredients that actually clean your hair — but they’re far from identical. Here’s what each one is, how they differ, and how to use that knowledge to choose a shampoo that suits your scalp.
SLS vs SLES vs SCI at a glance
Sodium lauryl sulfate (SLS) vs. sodium laureth sulfate (SLES)
SLS and SLES are both sulfate surfactants commonly used in cleaning products and shampoos. They sound nearly identical, and the difference comes down to how they’re made. When SLS goes through a process called ethoxylation, it becomes SLES — a change that makes the surfactant somewhat gentler and less irritating. Both are still considered strong, effective cleansers, so both can strip natural oils if your scalp is on the dry or sensitive side.
What is sodium cocoyl isethionate (SCI)?
SCI is also a surfactant, but a much gentler one. It’s derived from coconut oil fatty acids and isethionic acid, and it’s prized for creating a rich, creamy lather that removes buildup while staying mild on the skin. We use SCI in our shampoo bars precisely because it’s gentle and highly effective — you get a satisfying lather and a clean scalp without the strip-and-rebound cycle harsher detergents can cause.
Is SCI a sulfate?
No. Despite often appearing in conversations about sulfates, sodium cocoyl isethionate is not a sulfate. It’s a coconut-derived isethionate surfactant, which is why it can be both effective and gentle — and why a shampoo can be sulfate-free while still cleaning beautifully.
Is SLS bad for your hair?
SLS is a controversial ingredient because of its potential to irritate. Research has found it can disrupt the skin barrier by disturbing the skin’s lipid composition, increasing trans-epidermal water loss (drying out the skin) and causing irritation. Concentration matters, though: SLS is more likely to be damaging at higher concentrations and may be less irritating at lower ones. For many people — especially those with dry, curly, or color-treated hair — a gentler surfactant simply feels better day to day.
Every shampoo needs a surfactant to clear away buildup, dirt, grime, and dead skin cells — there’s no such thing as a shampoo without one. Surfactants reduce the surface tension of liquid so it can spread and break down oil, which is exactly what cleansing your hair requires. But not all surfactants are equal: they vary in strength, which makes some far more stripping than others.
A shampoo’s “strength” is essentially how rapidly and effectively it breaks down hair soils — sebum, dead skin, pollutants, and product residue — through emulsification, penetration, and solubilization. SLS and SLES both rank as strong surfactants on that scale, while SCI sits at the gentler end.
Clarifying vs. gentle: what kind of shampoo is best?
Only you can decide what’s best for your hair, based on your hair type, ingredient preferences, and goals — but product descriptions give you useful clues:
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Clarifying shampoos are stronger and potentially more drying. They’re useful for removing buildup, but they’re best used only a few times a month rather than every wash. (Note: a shampoo can be clarifying without sulfates.)
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Gentle shampoos are less stripping. They still contain surfactants — just milder ones, like sodium cocoyl isethionate — so they’re well suited to most wash days.
If you wash a few times a week, a gentle shampoo will handle the job most of the time. When hair is especially dirty, a little extra shampoo or a quick double wash usually does the trick.
Our sulfate-free shampoo bars
We formulate our shampoo bars without sulfates, using SCI instead, because of the potential irritation and dryness sulfates can cause. That makes the bars more universally accessible and safe for all hair types — curly, kinky, and color-treated included. With plant-based ingredients and plastic-free packaging, they’re also far lighter on the planet than a typical bottled shampoo.
Ready to make the switch? Try a single Shampoo Bar, pair it with a Conditioner Bar for tangle-free ends, or get both together in our bestselling Shampoo & Conditioner set.
Frequently asked questions
Is SCI a sulfate?
No. Sodium cocoyl isethionate (SCI) is a gentle, coconut-derived surfactant, not a sulfate. A shampoo made with SCI can be labeled sulfate-free while still lathering and cleaning effectively.
What’s the difference between SLS and SLES?
They’re both sulfate surfactants. SLES is SLS that has been ethoxylated, which makes it somewhat gentler and less irritating — but both are still strong, potentially stripping cleansers.
Is SLS bad for your hair?
SLS isn’t toxic, but it can irritate and dry the scalp by disrupting the skin barrier, especially at higher concentrations. If your scalp feels tight or irritated, a gentler, sulfate-free shampoo is often a better fit.
Is sulfate-free shampoo better?
Not universally — it depends on your hair and scalp. But for dry, curly, color-treated, or sensitive hair, a sulfate-free formula with a mild surfactant like SCI is usually gentler. The Earthling Co.’s shampoo bars are sulfate-free and suit all hair types.
Do sulfate-free shampoos still lather?
Yes. SCI in particular creates a rich, creamy lather, so a sulfate-free bar can feel just as satisfying to use as a conventional shampoo.
The bottom line
SLS, SLES, and SCI all clean your hair, but they sit at very different points on the gentleness scale — and SCI isn’t a sulfate at all. Once you know what to look for on a label, choosing a shampoo gets a lot easier. If you want a gentle, sulfate-free option that’s kind to your scalp and the planet, start with our bestselling Shampoo & Conditioner set, build a full routine with the Earthling Starter Kit, or create your own routine and save 35%.
Related reading: What Are Surfactants and Why Do We Use Them? · Why Are Sulfates Bad for Hair? · Eco-Friendly Hair Care Products Worth the Switch in 2026.
