Are sulfates bad for your hair?

What actually decides how harsh a shampoo is?

The whole surfactant system, and the scalp it lands on.

A shampoo is a blend of cleaning ingredients, not one single detergent. Usually one main surfactant does most of the cleaning, while smaller amounts of others adjust how strong the whole mix feels. Removing sulfates from that blend does not tell you what replaced them or how strongly the replacement cleans. Some sulfate free formulas are milder than the sulfate version they replaced. Some are not. The word on the front does not tell you which one you have.

Then there is the other half, which the label cannot know: your scalp. The same shampoo can be a good match for an oily scalp with product buildup and a bad match for a dry, easily irritated one. How harsh a shampoo feels depends on both the formula and the scalp it lands on.

Has anyone tested sulfates against the alternatives?

Yes, twice in ways we trust, and the results do not line up with the label.

Bujak and colleagues, at a university in Poland with no cleanser maker on the paper, took four detergents that turn up in shampoos and tested them at the same 1% strength in the same lab: SLS, sodium coco sulfate, SLES and sodium lauroyl sarcosinate. They measured how much corn protein each one dissolves, which stands in for how hard it attacks the proteins in skin, and they also measured degreasing power and what each one did to skin cells in a dish. SLS was harshest by a wide margin. SLES came out mildest of the four, and the sarcosinate, which is sold as the gentle sulfate-free choice, scored worse than SLES.

Vozmediano and colleagues, at the University of Cadiz, put four cleansers on human skin at the same 5% strength and measured irritation with instruments. Decyl glucoside was gentlest, then cocamidopropyl betaine, then magnesium laureth sulfate, then SLES. So in that test a sulfate-free cleanser did win, but a different one, and only against SLES, not against the whole sulfate family.

Put the two together and the label falls apart as a guide. One sulfate beat a sulfate-free detergent on a protein test, and one sulfate-free detergent beat a sulfate on skin. What decided each result was the exact molecule and how much of it was used, which is what the word on the front never tells you.

Both tests have limits you should know. The Polish test used corn protein in a beaker and cells in a dish, not skin, so nothing it found is a scalp result. The Spanish test was a patch on skin, not a shampoo rinsed off a scalp, and its published summary gives no numbers. Neither tested a full shampoo, where the main cleanser is cut with milder ones. They rank molecules; they do not rate bottles.

Why does pH matter more than the sulfate label?

Because pH has a measured effect behind it, and the sulfate label does not.

A shampoo's pH changes the electric charge on the surface of your hair, and that charge decides how much your strands catch on each other. A mildly acidic shampoo keeps the cuticle flat and friction low. An alkaline one raises the charge, lifts the cuticle, and is linked to more frizz, damage, and breakage. A survey of 123 shampoos found a pH range from 3.5 to 9.0, with only about 38% at or below 5.5.

Read the full breakdown of shampoo pH, including the category-by-category data and why there is no single correct number.

When are sulfates the right choice?

When there is something on the hair that needs removing.

Sulfates clean efficiently, which is exactly what you want when buildup is the problem. That includes leftover styling product and, specifically, water insoluble silicones such as dimethicone, which will not rinse out in a normal wash and need stronger cleaning power to clear. If your routine uses those, washing hard once in a while is not a mistake. It is the other half of the system doing its job.

An oily scalp carrying stale, oxidised oil is the other clear case. There, cleaning thoroughly is the actual goal, not something to avoid.

Who should be careful with sulfates?

Dry scalps, easily irritated scalps, and anyone running strong cleansing on repeat rather than as needed.

The same silicone review that explains why strong surfactants are sometimes needed also explains the cost of overusing them: too much strong cleansing strips natural lipids and can leave the cuticle dry or rough, and that hits delicate or textured hair hardest. Sulfates by themselves are not the real problem. Heavy, water insoluble silicone paired with frequent, aggressive stripping, kept up for months, is.

So think about how often you use it and whether it fits your scalp, rather than avoiding sulfates outright. A sulfate shampoo used when there is buildup to clear is a useful tool. The same shampoo used every day on a dry scalp is the wrong match.