Around 2010 the sulfate-free movement took off. By 2020, "no sulfates" had become a standard claim on shampoo packaging, sitting next to "no parabens" and "no silicones" as a signal of safety. The assumption behind it: sulfates are harsh, and harsh is bad.
The science is less categorical. Sulfates — specifically sodium lauryl sulfate (SLS) and sodium laureth sulfate (SLES), the two most common in shampoos — are effective cleansers with real tradeoffs. Whether those tradeoffs matter for your hair depends on what your hair is actually like, not on the ingredient's reputation.
What sulfates are and what they do
Sulfates are a type of surfactant — a cleansing agent that works by forming microscopic structures called micelles around oil and debris on the hair and scalp, which then rinse away with water. They're highly effective at this. SLS in particular has been a standard cleansing ingredient in shampoos for decades, and a comprehensive review of shampoo surfactant technology confirms it remains among the most efficient cleansers available.[1]
The tradeoff is that it's not selective about what it lifts. Along with sebum (the natural oil produced by the scalp, which builds up on the hair), SLS also removes some of the hair's own protective lipids — the internal and surface oils that help maintain the cuticle structure, regulate moisture permeability, and give hair its natural resilience. A systematic review of hair lipid composition found that lipid loss from repeated surfactant use leads to dehydrated, more breakage-prone hair over time.[6]
Sodium laureth sulfate (SLES) is a close relative of SLS with an additional processing step that results in a larger molecular structure. That difference matters: SLES is meaningfully gentler. Patch testing comparing the two surfactants found a pronounced skin reaction to SLS, a far milder one to SLES, and in the case of alkyl polyglucosides (the gentlest common surfactant category), a reaction that was barely detectable.[2] The irritant potential scales down clearly across the three.
The scalp versus the strand
Most of the evidence on sulfate irritation comes from skin research — patch testing and wash studies that measure how surfactants affect the scalp and skin. That evidence consistently shows that SLS is more irritating than alternatives at equivalent concentrations, and that the irritation is measurable and cumulative.[3]
What's less studied is the direct effect on the hair strand itself, distinct from the scalp. Hair and skin are structurally different. The hair shaft is not a living tissue and doesn't mount an immune response to surfactants the way skin does. What it does do is absorb and release surfactant molecules during washing, and repeated exposure contributes to lipid loss and the creation of pores — low-density areas — within the fiber.
Research into this mechanism found that repeated surfactant treatment created areas of reduced internal density in hair, and that the more severe the cuticle lifting (from prior damage or porosity), the greater the effect.[4] Sealing the cuticle after washing limited this. The implication: sulfate damage to the hair strand is real, cumulative, and made worse by existing damage — which is exactly the situation in chemically processed or high-porosity hair.
Sulfates and lipid loss
The relationship between surfactants and the hair's lipid content is where the "sulfates are bad" argument has its strongest footing — and also its most important nuance.
Shampoos and conditioners contain surfactants that remove lipids during routine cleansing. But as one review of hair lipid structure noted, shampooing does not completely remove all free lipids from the surface layers, and the effect of surfactants on the structural lipids deeper within the fiber is still not fully understood.[5] Lipid loss happens. How much, under what conditions, and whether it's reversible varies.
The relevant factors are: how stripping the surfactant is (SLS more so than SLES, which is more so than glucosides), how frequently you wash, and how compromised the hair's existing lipid barrier is. For virgin hair washed twice a week, SLS-based shampoo may have minimal noticeable impact. For bleached, daily-washed hair with already-depleted lipids, the same shampoo accelerates a problem that's already in progress.
“Sulfates are not inherently harmful and sulfate-free is not inherently better. The right question is whether your hair needs the level of cleansing a sulfate shampoo provides.”
When sulfate-free is the right call
Sulfate-free shampoos use gentler surfactant alternatives — SLES, glucosides, amino acid-derived surfactants, or combinations — that clean less aggressively and strip fewer lipids per wash. They tend to produce less lather (foam is mostly cosmetic; it doesn't indicate cleaning power), and they may not remove heavy product buildup as effectively.
The situations where sulfate-free makes sense from an evidence standpoint:
Color-treated or bleached hair. Chemical processing depletes lipids and raises porosity. More stripping surfactants compound that existing damage wash by wash. An open-wash study confirmed that even modest SLS exposure causes measurable subclinical surface changes in skin after only three washes — damage that accumulates.[7] In bleached hair, the cuticle is already compromised, and additional lipid stripping is worse than in undamaged hair.
High-porosity or chronically dry hair. If your hair already struggles to retain moisture, a surfactant that further strips protective lipids is working against the same goal your conditioner is working toward. Gentler surfactants reduce the net damage per wash cycle.
Scalp sensitivity. If you experience scalp irritation, dryness, or flaking after washing, the surfactant is a reasonable variable to change. Moving from SLS to SLES or glucoside-based formulas often helps. This is a scalp issue, not a hair issue, but the two are usually addressed by the same shampoo.
Natural or low-manipulation styles. Hair that's washed less frequently can accommodate a gentler formula that may not cut through heavy buildup as efficiently.
When sulfate shampoos are fine
Sulfates became a marketing villain, not because the ingredient is inherently dangerous, but because "sulfate-free" was a differentiator that was easy to label. Most people washing undamaged hair, without scalp sensitivity, at normal frequency don't have a meaningful problem with SLS.
Undamaged hair, washed occasionally. If you're not bleaching, not heat-styling daily, and washing two to three times a week, the lipid stripping per wash is likely within what your hair can manage between washes.
Removing silicone-heavy product buildup. If your routine uses silicone-based products — serums, heat protectants, finishing sprays — gentle surfactants often can't remove the buildup effectively. An occasional clarifying wash with a stronger formula prevents accumulation.
Oily scalps that need thorough cleansing. If excess sebum is consistently a problem, a more effective cleanser solves a real issue. Switching to sulfate-free and washing more frequently to compensate often results in the same lipid stripping in smaller, more frequent doses.
The honest answer is that sulfates are not inherently harmful and sulfate-free is not inherently better. The right question is whether your hair and scalp need the level of cleansing a sulfate shampoo provides — and whether the tradeoffs of that cleansing outweigh the benefits given your hair's current condition.
How to decide
The most useful framing: think about your hair's porosity and damage history, your scalp's sensitivity, and your wash frequency. Then match those to the surfactant strength your shampoo provides.
High-porosity, chemically treated, or sensitive-scalp hair benefits from the gentlest surfactants available — SLES at minimum, glucoside or amino-acid based at best. Low-porosity, undamaged hair being washed infrequently can generally tolerate SLS without cumulative harm. Most hair is somewhere in between, and SLES-based formulas are often the right middle ground.
ROOTS' product analysis includes surfactant type as part of how shampoos are evaluated for your hair profile. If you've taken the ROOTS quiz, your matched products already account for this — you're not filtering for "no sulfates" or "with sulfates," but for the cleansing level your specific hair actually needs.