Hair Colour vs. Shampoo Ingredients — How to Make Your Colour Last?

Why colour fades — the mechanism of pigment washout

Permanent hair dyes (the oxidative type) work in two stages: first, an alkaline environment (ammonia or MEA) lifts the cuticle, and then hydrogen peroxide oxidises the colour precursors inside the cortex, forming large pigment molecules. These molecules are too big to leave the hair on their own — but an open cuticle gives them an escape route.

Every wash is a potential attack on the pigment. Water, surfactants and mechanical friction cause the cuticle to lift, and the soluble pigment fractions wash out. The harsher the shampoo, the faster you lose your colour. Research in the Journal of Cosmetic Science has shown that shampoos with a pH above 6.0 cause pigment to fade up to twice as fast as shampoos with a pH of 4.5–5.0.

SLS and SLES — why do sulfates destroy colour?

Sodium Lauryl Sulfate (SLS) and Sodium Laureth Sulfate (SLES) are anionic surfactants with a very strong cleansing action. They work by forming micelles that dissolve sebum and dirt — but, in the process, they also strip out cosmetic pigments. Check the details in our ingredient encyclopaedia.

SLS is especially problematic because it:

• Lifts the cuticle — as an anionic surfactant with a pH of 5.0–6.5 (in solution), it loosens the cuticle scales and makes pigment washout easier
• Has a hygroscopic effect — it draws water into the hair shaft, causing it to swell and the cuticle to open further
• Dissolves lipids — it removes the 18-MEA layer that protects the hair's surface

SLES (with the added "Eth" — meaning ethoxylated) is milder than SLS, but it is still considerably more aggressive than sulfate-free alternatives.

Sulfate-free shampoos — what replaces sulfates?

"Sulfate-free" shampoos replace SLS/SLES with gentler surfactants that cleanse effectively without opening the cuticle so aggressively:

• Cocamidopropyl Betaine — an amphoteric surfactant with a pH close to 5.0. Mild, lathers well and doesn't disturb the cuticle
• Sodium Cocoyl Isethionate (SCI) — anionic, but far milder than SLS. Derived from isethionic acid and coconut oil
• Decyl Glucoside — a non-ionic surfactant from the alkyl glucoside family. Biodegradable and exceptionally gentle. Popular in natural cosmetics
• Sodium Lauroyl Methyl Isethionate — a mild anionic surfactant that produces good lather without acting aggressively on the cuticle

It's worth knowing that "sulfate-free" doesn't automatically mean "gentle" — what matters is the whole formula, the pH and the concentration of surfactants. A shampoo without sulfates but with a very high pH can still open the cuticle. Compare formulas in the shampoos category on PurScore.pl.

Acidic pH — the single most important factor for colour

A shampoo's pH is arguably more important than the type of surfactant. The hair cuticle closes in an acidic environment (pH 3.5–5.0) and opens in an alkaline one (pH above 6.0). A closed cuticle means the pigment can't escape.

The optimal pH for a shampoo for colour-treated hair is 4.5–5.5. Unfortunately, most manufacturers don't print the pH on the label. It's worth investing in litmus paper (pH 1–14, around 10 PLN) and measuring the pH of your products yourself.

An extra tip: a final rinse with cool, slightly acidified water (a spoonful of apple cider vinegar per litre of water) after every wash closes the cuticle and slows colour loss. This simple step can extend how long your colour lasts by 2–3 weeks.

Colour-depositing conditioners

Colour-depositing conditioners contain direct dyes that settle on the surface and within the cuticle layers, topping up your colour between salon visits. The most common pigments are:

• HC Blue/Red/Yellow — small-molecule pigments that partially penetrate the cuticle
• Basic Blue/Red/Brown — cationic pigments that bind electrostatically to the negatively charged surface of the hair

The effect is temporary (4–8 washes), but using a colour-depositing conditioner 1–2 times a week keeps the colour vibrant without exposing your hair to another round of chemical colouring. Check available products in the PurScore search engine.

UV filters for hair — the underrated essential

UV radiation breaks down the pigments in your hair — both natural (melanin) and artificial (the pigments from dye). This process is called photodegradation. Colour-treated hair is particularly vulnerable, because synthetic pigments are less stable than melanin.

Ingredients that provide UV protection for hair:

• Ethylhexyl Methoxycinnamate (Octinoxate) — a UVB filter and one of the most widely used in hair products
• Benzophenone-4 — a water-soluble UVA/UVB filter that is effective in rinse-off products
• Butyl Methoxydibenzoylmethane (Avobenzone) — a UVA filter, but less stable — it requires stabilisers

UV filters in shampoos and conditioners have limited effectiveness (you rinse them off). They work best in leave-in products — mists, serums and hair oils. In summer, it's also worth wearing a head covering — that's the most effective UV protection of all.

A practical colour-care routine

1. Washing: sulfate-free shampoo, pH 4.5–5.5, no more than 2–3 times a week
2. Conditioner: after every wash, with proteins and emollients. Once a week, use a colour-depositing conditioner
3. Rinse: cool water with a splash of apple cider vinegar
4. Leave-in product: a serum or mist with UV filters
5. Overnight protection: a satin pillowcase or turban

Want to find out whether your shampoo is safe for colour-treated hair? Type its name into the PurScore.pl search engine — we'll show you whether it contains SLS, silicones and what its predicted pH is.