Why Does Colour Fade in the First Place?
Hair colour — whether permanent, semi-permanent, or direct dye — sits inside or on the surface of the hair shaft. The cuticle, which is the outermost protective layer, acts like a series of overlapping shingles. When anything causes those shingles to lift, dye molecules have a route out.
Water alone causes minor swelling of the cuticle. Add a shampoo formulated with aggressive cleansers or a high pH, and that swelling becomes significant enough to let colour leach into the rinse water. This is why what ingredients a shampoo contains matters far more than its marketing claims.
The rate of fade also depends on how the colour was applied. Permanent colour uses an oxidative process to deposit pigment inside the cortex, while semi-permanent and direct dyes coat the outside. Surface-deposited dyes are particularly vulnerable to the cleansing agents discussed below.
Which Sulfates Strip the Most Colour?
Sulfate surfactants are the workhorses of traditional shampoo formulas. They are anionic, meaning they carry a negative charge, and they are extremely effective at removing oils and product build-up. That same power is what makes them hard on colour.
Sodium lauryl sulfate (SLS) is the most studied example. Its small molecular size lets it penetrate the cuticle layer, where it disrupts the bonds holding dye in place. Sodium laureth sulfate (SLES) is chemically related but slightly larger and milder, yet still causes measurable colour loss with regular use. Both appear extensively in open-access cosmetic ingredient databases.
Ammonium lauryl sulfate and ammonium laureth sulfate behave similarly and are worth scanning for on a label. A sulfate-free shampoo typically replaces these with gentler alternatives such as cocamidopropyl betaine, sodium cocoyl isethionate, or sodium lauroyl methyl isethionate, all of which are documented in publicly available cosmetic ingredient resources.
- Sodium lauryl sulfate (SLS) — highest stripping potential among common surfactants
- Sodium laureth sulfate (SLES) — milder but still significant
- Ammonium lauryl sulfate — similar behaviour to SLS
- Ammonium laureth sulfate — common in budget formulas, still colour-active
What Role Does Shampoo pH Play?
The pH scale runs from 0 to 14. Healthy hair sits at roughly 4.5 to 5.5, which is mildly acidic. At this range the cuticle stays relatively flat and closed. Many standard shampoos, particularly those with high surfactant loads, have a pH closer to 6 or 7, and some clarifying products go higher still.
A higher pH causes the cuticle to swell open. With the cuticle lifted, colour pigment diffuses out during rinsing. This effect is well recognised in hair science literature and forms the basis of the industry-standard advice to use acidic rinses such as diluted apple cider vinegar after colouring.
Some brands now print their pH on the label or bottle, but many do not. If no pH is listed, looking at the ingredient list for buffering agents can give a rough clue. Citric acid, lactic acid, and sodium citrate appearing near the end of a list generally indicate the brand is making some effort to control pH downward.
What Are Chelating Agents and Why Do They Matter?
Chelating agents are added to shampoos primarily to bind mineral ions — calcium, magnesium, and iron — that enter the formula from hard water or water supply variation. By grabbing these ions, chelators prevent them from interfering with the surfactant system and reduce dullness caused by mineral build-up on the hair.
The most common chelating agent in shampoo is disodium EDTA (ethylenediaminetetraacetic acid). A related form, tetrasodium EDTA, also appears frequently. Both are listed in publicly available cosmetic ingredient databases maintained by regulatory bodies in the EU and US.
For colour-treated hair, the concern is that chelators do not stop at grabbing loose mineral ions. They can also interact with the metallic components of certain hair dyes and accelerate the breakdown of the colour bond. People in hard-water areas tend to notice more fading, partly because their shampoo's chelator is working harder with each wash.
Phytic acid and sodium gluconate are used as milder chelating alternatives in some newer colour-safe formulations. They are considered less aggressive toward dye bonds while still managing mineral build-up.
Do Fragrances and Alcohols Contribute to Fading?
Fragrance is almost always listed as a single entry on a cosmetic label, even though it may represent dozens of individual compounds. Some fragrance components are solvents that can slightly disturb the surface of the hair shaft and the dye sitting on or near it. The extent of this effect is not fully settled in the public scientific record.
Alcohol denat. (denatured alcohol) and isopropyl alcohol appear in certain shampoo formulations, particularly volumising or clarifying ones. These short-chain alcohols can temporarily lift the cuticle and, with repeated use, cause incremental colour loss. Fatty alcohols — such as cetyl alcohol or stearyl alcohol — behave differently; they are conditioning and do not carry the same risk.
If you are reading a label and uncertain which type of alcohol is listed, a simple rule applies: short names like 'alcohol denat.,' 'isopropyl alcohol,' or 'ethanol' are the drying, potentially colour-active forms. Longer names ending in '-yl alcohol' with a fatty origin are generally safe for colour-treated hair.
Are Clarifying and Anti-Dandruff Shampoos Especially Problematic?
Clarifying shampoos are designed to remove heavy build-up from silicones, styling products, and minerals. They achieve this through higher concentrations of sulfates or by using a more alkaline formula. Both strategies make them particularly aggressive on colour. Most hair professionals recommend using clarifying products before a colour service, not after.
Anti-dandruff shampoos typically contain active ingredients such as zinc pyrithione, selenium sulfide, or ketoconazole, all of which appear in regulatory databases as approved actives. Selenium sulfide in particular has a reputation for accelerating colour fade and is worth avoiding in routine washes on colour-treated hair. Zinc pyrithione-based formulas are generally considered less disruptive, though they are still more stripping than a purpose-formulated colour-safe shampoo.
If dandruff management is necessary alongside colour protection, a dermatologist or trichologist is the best person to advise on a rotation strategy. This post is educational and does not replace that kind of professional guidance.
What Ingredients Should You Look For Instead?
The positive side of ingredient reading is that a few markers reliably indicate a gentler formula. Betaine-based surfactants — particularly cocamidopropyl betaine — appear in most colour-safe shampoos as the primary cleansing agent. They are amphoteric, meaning they carry both positive and negative charges, and they clean effectively at a lower irritation and stripping cost.
Amino acid surfactants such as sodium cocoyl glutamate and sodium lauroyl glutamate are another strong indicator of a colour-conscious formula. They are naturally derived, well-documented in cosmetic ingredient compendia, and formulated at pH ranges that keep the cuticle flatter.
Conditioning polymers such as polyquaternium-10 and guar hydroxypropyltrimonium chloride deposit a light coating on the hair shaft with each wash, which can slow the rate at which colour molecules diffuse out. They are not a substitute for gentler surfactants, but they add a meaningful layer of protection.
InZoRAH can scan the barcode of any shampoo and flag the specific surfactants, chelators, and pH indicators on its label, so you can compare what ingredients two bottles actually share before buying either.
- Cocamidopropyl betaine — gentle amphoteric surfactant, widely used in colour-safe lines
- Sodium cocoyl glutamate / sodium lauroyl glutamate — amino acid surfactants, low stripping potential
- Citric acid or lactic acid — signals the brand is managing pH downward
- Polyquaternium-10 — conditioning polymer that helps seal the cuticle after washing
- Sodium gluconate or phytic acid — milder chelating alternatives to EDTA
How Can You Read a Shampoo Label More Quickly?
Ingredients on a cosmetic label in the US and EU must be listed in descending order of concentration. The first five to seven ingredients make up the bulk of the formula. If a sulfate surfactant appears in that opening group, the formula will clean aggressively regardless of what claims appear on the front of the bottle.
Words like 'colour safe,' 'gentle,' or 'for treated hair' are marketing descriptions and carry no regulated definition in the US, according to FDA labelling rules for cosmetics. The ingredient list is the only legally standardised section of the label.
A practical scanning approach: check positions one through seven for sulfates, check mid-list for EDTA variants, and look toward the end for pH-controlling acids. If you spot all three problem categories in one product, expect faster fading. If none appear, the formula is likely gentler on colour.
| Ingredient | Type | Colour Impact |
|---|---|---|
| Sodium lauryl sulfate (SLS) | Anionic surfactant | High — strips colour efficiently |
| Sodium laureth sulfate (SLES) | Anionic surfactant | Moderate to high |
| Disodium EDTA / tetrasodium EDTA | Chelating agent | Moderate — accelerates dye breakdown |
| Selenium sulfide | Anti-dandruff active | High — known to fade colour quickly |
| Cocamidopropyl betaine | Amphoteric surfactant | Low — colour-safe choice |
| Sodium cocoyl glutamate | Amino acid surfactant | Low — gentle on dye |
| Citric acid | pH adjuster | Protective — helps keep cuticle closed |
| Alcohol denat. / isopropyl alcohol | Solvent | Low to moderate with repeated use |
