Sodium laureth sulfate (SLES) is not inherently bad for hair, but it can cause dryness, frizz, and color fading depending on your hair type and how often you wash. It’s a milder cousin of sodium lauryl sulfate (SLS), the more irritating sulfate that gets most of the bad press. For people with straight, oily hair who wash a few times a week, SLES is generally fine. For those with curly, textured, color-treated, or naturally dry hair, it can strip away moisture your hair struggles to replace.
How SLES Differs From SLS
SLES and SLS are closely related but not identical. SLS is the base chemical, made by reacting lauryl alcohol with petroleum or plant-derived oils like coconut or palm. It has a small molecular structure: a 12-carbon chain on one end that grabs oil and grease, and a sulfate group on the other that dissolves in water. That compact size is what makes it an effective cleanser, but it also allows SLS to penetrate the outer layers of skin and hair more easily, disrupting the natural lipid barrier and denaturing proteins.
SLES starts as SLS but goes through an additional manufacturing step called ethoxylation, which attaches one to four ethylene oxide units to each molecule. This makes the molecule physically larger, which limits how deeply it can penetrate skin and hair. The result is a surfactant that still foams and cleans effectively but interacts less aggressively with biological tissue. That’s why SLES replaced SLS in most mainstream shampoos years ago.
What SLES Actually Does to Hair
SLES is an anionic surfactant, meaning it carries a negative charge that attracts and binds to oils, dirt, and product residue so they rinse away with water. The problem is that it doesn’t distinguish between the grime you want gone and the natural sebum your scalp produces to protect and moisturize your hair. When SLES strips that sebum layer, it leaves hair feeling “squeaky clean” but also more vulnerable to dryness and mechanical damage.
SLS-based shampoos have been shown to cause hair shafts to swell and cuticle layers to lift open. SLES is gentler in this regard, but the same basic mechanism applies: the surfactant disrupts the cuticle, the shingle-like outer layer of each strand that locks in moisture and reflects light. Once those cuticle layers are raised, hair loses its smoothness and shine, tangles more easily, and becomes more prone to breakage over time.
On the scalp, sulfate exposure increases transepidermal water loss, a measure of how much moisture escapes through the skin. Research on SLS shows that after a single exposure, the scalp’s moisture barrier can take two to five days to fully recover, with significant variation between individuals. Some people’s skin bounces back quickly while others remain compromised longer. SLES produces a less dramatic version of this effect, but daily or frequent washing can keep the scalp in a cycle of damage and partial recovery.
Hair Types That Are Most Affected
Curly and coily hair is naturally drier than straight hair because the oils your scalp produces have to travel down twists and bends in each strand rather than sliding straight to the tips. That means curly hair starts with less protective sebum along its length. Using a sulfate shampoo compounds the problem by stripping what little oil is there, leading to dryness, brittleness, frizz, and poorly defined curl patterns. This is one reason the “curly girl method” and similar routines specifically avoid sulfates.
Fine or thin hair can also suffer, though for a different reason. These strands have a thinner cuticle layer to begin with, so they’re more susceptible to the protein disruption and swelling that sulfates cause. Color-treated and chemically processed hair is vulnerable too, since the cuticle has already been deliberately opened during the coloring or relaxing process, making it easier for surfactants to penetrate and cause further damage.
If you have thick, straight, oily hair and no chemical treatments, SLES is unlikely to cause noticeable harm with normal use.
SLES and Hair Color Fading
One of the most common reasons people switch to sulfate-free shampoos is to preserve hair color, and there’s real science behind that instinct. When researchers soaked dyed hair in a 1% SLES solution, the surfactant increased dye dissolution by 47% compared to water alone after one hour. That’s a meaningful amount of color loss from a single exposure. Over weeks of regular washing, the cumulative effect adds up to noticeably faster fading, especially for reds and other vibrant shades that are already prone to washing out.
Interestingly, the same study found that certain cationic (positively charged) surfactants, the type often found in conditioners, actually pulled out even more dye than SLES. So the full picture of color preservation involves not just your shampoo but your entire wash routine, water temperature, and how often you wash.
The 1,4-Dioxane Concern
Beyond direct effects on hair, SLES carries a manufacturing-related concern that comes up frequently in clean beauty circles: contamination with 1,4-dioxane. This chemical is not an intentional ingredient. It forms as a byproduct during the ethoxylation process that converts SLS into SLES.
The U.S. EPA classifies 1,4-dioxane as likely carcinogenic to humans. In animal studies, it has caused tumors in the liver, nasal cavity, kidneys, mammary glands, and lungs. It is also toxic to the liver, kidneys, nervous system, and respiratory system at higher exposures. California’s Department of Toxic Substances Control has flagged it as a persistent, mobile, and toxic chemical that standard water treatment cannot remove, meaning it also poses an environmental concern when it washes down your drain.
Manufacturers can reduce 1,4-dioxane levels through vacuum stripping, a purification technique that can cut contamination by ratios of 40:1 to 100:1 in a single pass. Chemical oxidation using hydrogen peroxide is another method that breaks the compound down into carbon dioxide and water. Reputable manufacturers do purify their SLES, but because 1,4-dioxane is a contaminant rather than an ingredient, it typically doesn’t appear on product labels. The actual amount in any given shampoo bottle varies by manufacturer and is difficult for consumers to verify.
Sulfate-Free Alternatives
If you decide SLES isn’t right for your hair, sulfate-free shampoos use milder surfactants to clean without the same degree of oil stripping. Common alternatives include cocamidopropyl betaine, decyl glucoside, and sodium cocoyl isethionate. These produce less foam, which can feel like they’re not cleaning as well, but lather has nothing to do with how effectively a shampoo removes dirt.
The tradeoff is that gentler surfactants may not cut through heavy product buildup or very oily scalps as efficiently. Some people find that alternating between a sulfate-free shampoo for regular use and an occasional SLES-based clarifying wash gives them the best of both worlds. This approach removes accumulated silicones and styling products without the daily stripping that causes long-term dryness.
Co-washing (using conditioner only) is another option popular in curly hair communities, though it can lead to buildup over time if not periodically followed by a cleansing wash. The right approach depends on your hair texture, how much product you use, and how your scalp responds.