KeraWhat sulfates in shampoo actually do, and who should avoid them
SLS and SLES clean well, and that is the entire indictment. What the evidence says about irritation, colour fade and hair loss, and the four groups who genuinely benefit from avoiding them.
The short answer
The sulfates in shampoo — sodium lauryl sulfate and sodium laureth sulfate — are efficient anionic surfactants. They clean thoroughly, which on a dry scalp or very damaged hair can be more than you want. They do not cause hair loss, they are not carcinogenic, and the colour-fade case against them is weaker than the marketing suggests. Avoiding them makes real sense for sensitive or eczema-prone scalps, very dry or coily hair, keratin-treated hair, and anyone whose hair simply feels better without them.
Somewhere around 2010, "sulfate-free" went from a niche formulation choice to a moral position. It is now printed on shampoo, conditioner, and occasionally on products that could not contain a sulfate if they tried.
The chemistry is much less dramatic than the label.
What the sulfates in shampoo are
A surfactant is a molecule with a water-loving end and an oil-loving end. That structure is what lets it surround sebum and carry it away in the rinse. Every shampoo contains surfactants; the only question is which.
Sodium lauryl sulfate (SLS) is a small, highly effective anionic surfactant. It is also the standard positive control in skin irritation studies — when researchers need a known irritant to compare something against, they reach for SLS. That is an accurate reason to treat it with respect, and also the source of most of the fear, because "used as an irritant in studies" gets repeated without the concentrations involved.
Sodium laureth sulfate (SLES) is SLS with ethylene oxide added, which makes the molecule larger and considerably milder. This is what is actually in most mainstream shampoos, and conflating the two is the most common error in sulfate discourse.
The three claims, examined
"Sulfates cause hair loss." No. Surfactants act on the hair shaft and the skin surface during a wash lasting under a minute. They do not reach the follicle in any way that would affect the growth cycle. Shedding that appears after switching shampoo is nearly always coincidental, or the release of already-detached hairs by a wash that was more thorough than the previous one.
"Sulfates strip colour." They accelerate fade compared with milder surfactants, but the effect is smaller than marketing implies, and the biggest drivers of colour loss are water itself, heat, UV and time. If you wash a coloured head daily in hot water, changing the surfactant will not save it. The colour fade guide covers what actually matters.
"Sulfates are carcinogenic." This is straightforwardly false and has been for thirty years. It originated in a widely circulated hoax email and has been examined and dismissed by cosmetic safety review bodies repeatedly.
Who should actually avoid them
Four groups, with reasons that hold up.
Sensitive, eczema-prone or dermatitis-prone scalps. Barrier-compromised skin reacts to things intact skin ignores. If your scalp is tight, itchy or red after washing, switching surfactants is a rational experiment — as is washing in cooler water, which people try second and should try first.
Very dry, coarse or coily hair. The tighter the curl, the harder it is for sebum to travel down the fibre, so the lengths are chronically drier. A thorough cleanse removes protection this hair cannot easily replace. Gentler surfactants, or scalp-only cleansing, make obvious sense here.
Keratin-treated hair. Formaldehyde-based smoothing treatments genuinely degrade faster with strong anionic surfactants. This one is not marketing.
Anyone whose hair simply feels better. This is a legitimate reason and needs no theory behind it. Hair is a thing you live with daily; preference counts.
What you get instead, and the catch
Sulfate-free shampoos use other surfactants: cocamidopropyl betaine, sodium cocoyl isethionate, coco-glucoside, decyl glucoside, sodium methyl cocoyl taurate.
They are generally milder. They also foam less, which most people read as "not cleaning", and they remove less water-insoluble material — which is the actual catch. If your routine includes silicones, heavy oils, dry shampoo or styling polymers, a gentler surfactant may not keep up, and you end up with buildup and a hair-feels-coated complaint that you then blame on the products rather than the shampoo.
This is why the sulfate-free and silicone-free recommendations travel together. They are a package, and adopting half of it is how people end up worse off than when they started.
It is also worth noting that cocamidopropyl betaine — a staple of gentle formulations — was the American Contact Dermatitis Society's Allergen of the Year in 2004. "Gentler on average" is not "gentle for you".
The practical position
If your scalp is comfortable and your hair feels fine, sulfates are not a problem you have. Buy on how the product performs, not on what it excludes.
If your scalp is irritated, run the cheap experiments first — cooler water, better technique, thorough rinsing — and then, if it persists, try a milder surfactant for a month.
And if you switch, switch the rest of the routine with it: lighter conditioners, fewer non-soluble silicones, and a clarifying wash every few weeks to catch what the milder shampoo leaves behind.
Common questions
Is SLS the same as SLES?
No. Sodium lauryl sulfate is the smaller, more irritating molecule. Sodium laureth sulfate has been ethoxylated, making it milder, and it is what most mainstream shampoos actually use.
Do sulfates cause cancer?
No. That claim originated in a chain email in the 1990s and has been examined and rejected repeatedly since.
Will sulfate-free shampoo fix my dry hair?
It might help at the margin, but dryness usually has bigger causes — heat, bleach, hard water, too few conditioning steps. Changing surfactant alone rarely transforms anything.
Kera offers hair-care lifestyle suggestions, not medical advice. It does not diagnose or treat any condition.