Sulfates, Chelating Agents, and Hot Water: What Ingredients Fade Colour-Treated Hair

Why does shampoo fade colour-treated hair at all?

Artificial dye sits mainly inside the hair cortex, the dense inner layer beneath the cuticle scales. To reach the cortex during colouring, the cuticle must be forced open — typically by the alkaline developer in the dye kit. After rinsing, the cuticle should close back down and trap the pigment inside.

The problem is that many everyday shampoo ingredients repeat that opening process every single wash. Surfactants, chelating agents, and pH levels all influence how tightly or loosely the cuticle lies flat. When the cuticle stays even slightly raised, smaller dye molecules — particularly the cool tones that make up ash and violet shades — migrate out with the rinse water.

This is not new knowledge, but a 2025 revision to the International Cosmetic Ingredient Dictionary tightened how formulators are expected to categorise surfactant mildness, which means the ingredient labels on newer bottles may look different even when the chemistry is familiar. Understanding what ingredients to look for is more useful than ever.

How does sodium lauryl sulfate strip colour so quickly?

Sodium lauryl sulfate, universally abbreviated as SLS, is an anionic surfactant derived from lauryl alcohol. It carries a strong negative charge that binds aggressively to the proteins in the hair shaft. That binding action lifts cuticle scales while it cleans, and each lift creates a window for dissolved pigment to escape.

SLS also has a relatively high pH on its own — typically between 7 and 9 in aqueous solution — which compounds the cuticle-swelling effect. Research cited by cosmetic chemists in open-access formulation literature consistently places SLS at the top of the list for pigment removal per wash cycle.

If SLS appears first or second in a shampoo's ingredient list, the product will clean powerfully. That is exactly what you want for oily, uncoloured hair and exactly what you do not want if you paid for a salon colour.

Is sodium laureth sulfate (SLES) any better for coloured hair?

Sodium laureth sulfate is the ethoxylated cousin of SLS. The ethoxylation process adds ethylene oxide units to the molecule, making it larger and slightly less able to penetrate the cuticle layer. It is meaningfully gentler than SLS, which is why colour-care shampoos that still contain a traditional sulfate almost always choose SLES over SLS.

Even so, SLES is still an anionic surfactant with a pH tendency above the hair's ideal acidic range. Used daily on freshly coloured hair, it produces cumulative fade. The practical difference between SLS and SLES is a matter of degree rather than kind.

Some brands now list ammonium laureth sulfate or sodium myreth sulfate as primary surfactants. These behave similarly to SLES and carry equivalent cautions for colour longevity.

What role do chelating agents like EDTA play in stripping colour?

Chelating agents are added to shampoos to bind the calcium, magnesium, and iron ions that accumulate from hard tap water. Without them, mineral deposits would make hair feel dull and stiff, and they would also neutralise the cleaning power of surfactants. So chelators do a real job — but they come with a trade-off for coloured hair.

Tetrasodium EDTA and disodium EDTA are the most common examples. They work by grabbing onto metal ions, but they can interact with the metallic components of some permanent dyes and, in the process, help displace pigment from the cortex. The effect is strongest on dark, metallic-pigment-rich shades such as deep reds and burgundies.

Citric acid also functions as a mild chelator in rinse-off products. Its presence is not automatically problematic — at low concentrations it primarily adjusts pH downward, which actually helps colour retention. At higher concentrations, or in leave-on products, its chelating action becomes more relevant. Checking where it falls in the ingredient list gives a rough sense of its concentration.

Phytic acid and sodium gluconate are newer chelator alternatives appearing in colour-safe formulations. Early formulation data suggests they are less likely to interact with dye molecules, though independent peer-reviewed confirmation remains limited as of late 2026.

Why does pH matter as much as the surfactant choice?

The hair cuticle behaves like a pH-sensitive structure. At a pH below roughly 4.5 to 5.5, the cuticle scales lie flat and compact. Above that range they begin to swell and separate. A shampoo with a pH of 7 or higher — which is common in basic formulas that have not been deliberately acidified — keeps the cuticle in a semi-open state for the entire wash.

This matters because even a sulfate-free surfactant blend will cause faster colour fade if the formula's overall pH is too high. The surfactant grabs dirt and oil; the elevated pH keeps the door to the cortex open while it does so.

The FDA does not set a mandatory pH range for rinse-off cosmetics, but cosmetic chemists and the personal care industry broadly recognise the 4.5–5.5 range as optimal for colour retention. A growing number of brands now print pH values on pack or on their websites as a differentiating claim. If a shampoo does not disclose its pH, an ingredient analyzer like InZoRAH can flag the high-pH surfactants present so you can make a more informed choice.

Are there other ingredients worth watching on the label?

Isopropyl alcohol and SD alcohol 40 appear in some volumising and clarifying shampoos. At the concentrations used in rinse-off products they are primarily solvents that help other ingredients distribute evenly, but they can also loosen the lipid layer on the cuticle surface, indirectly aiding pigment escape. They are a secondary concern rather than a primary one.

Sodium chloride — ordinary table salt — is used as a thickener in many sulfate-based shampoos. On colour-treated hair, high salt concentrations can draw moisture out of the shaft osmotically and, with repeated use, contribute to cuticle roughness. It is not a dye stripper in the way SLS is, but it nudges conditions in the wrong direction.

Fragrance ingredients including certain terpenes and citrus-derived compounds can have a mildly oxidising effect at higher concentrations. The practical impact on colour is small compared with sulfates and chelators, but it is a real consideration for people who wash frequently and are already battling rapid fade.

• Isopropyl alcohol and SD alcohol 40: secondary concern, primarily a solvent effect
• Sodium chloride: affects cuticle texture over time, not a direct dye stripper
• High-concentration fragrance terpenes: minor oxidative effect with frequent washing

What ingredients should colour-treated hair look for instead?

Coco-glucoside, decyl glucoside, and sodium cocoyl isethionate are non-ionic or mild anionic surfactants that clean without the aggressive cuticle-lifting of traditional sulfates. They appear in most credible color-safe lines and are well-documented in the FDA's voluntary cosmetic registration data and the INCI dictionary.

Behentrimonium chloride and cetrimonium chloride are cationic conditioning agents that carry a positive charge. Because hair carries a net negative charge, these ingredients are drawn to the cuticle surface, smoothing it flat. A formula combining a mild surfactant with one of these conditioners is the standard approach to colour protection.

Hydrolysed proteins — wheat, quinoa, and keratin — are frequently listed in colour-care shampoos. They temporarily fill micro-gaps in the cuticle, reducing the channel through which pigment can escape. Their effect is wash-by-wash rather than permanent, so their presence in a shampoo is genuinely useful rather than purely cosmetic marketing.

How do you read a shampoo label quickly at the shelf?

Ingredient lists run from highest to lowest concentration. If sodium lauryl sulfate or sodium laureth sulfate appears in the first four ingredients, the formula is surfactant-heavy and likely to accelerate fade. If the list opens with water followed by a glucoside or isethionate surfactant, that is a meaningful indicator of a gentler wash.

Look for EDTA variants in the mid-list. Their position matters: in the top half of a long ingredient list they are present at functional concentrations; in the bottom quarter they are likely below one percent and less consequential.

Using a dedicated ingredient checker at the shelf takes seconds and removes the guesswork from label reading entirely. What ingredients show up in the first six lines of that list will tell you most of what you need to know about how a shampoo will treat your colour.