Hair Dye vs Colour Shampoo — Longevity and Effect on Hair

Hair dye or colour shampoo — what's it all about?

Colouring your hair is one of the most popular forms of care and styling. The market, however, offers products with completely different mechanisms of action: hair dyes (oxidative or non-oxidative) and colour shampoos, which deposit colour only on the surface of the hair. Choosing between them isn't obvious — it depends on the longevity you want, the condition of your hair and your tolerance to specific active ingredients.

How does hair dye work?

Classic oxidative dyes contain two key components: dye precursors (e.g. p-phenylenediamine (PPD), resorcinol) and an oxidiser — most often hydrogen peroxide (H₂O₂). The oxidation reaction lifts the hair's cuticle, allowing the dyes to penetrate into the cortex. There they react with the natural melanins, forming durable, large dye molecules that the hair does not lose when washed.

Ammonia-free dyes work in a similar way, but instead of ammonia they use gentler alkanolamines (e.g. monoethanolamine, MEA), which raise the hair's pH less aggressively. It's worth remembering, though, that a lower pH does not always mean there's no risk of damage — hydrogen peroxide is itself an oxidising substance.

Looking for specific colouring products? Head to the hair dye category on PurScore.pl and compare formulations.

How does colour shampoo work?

Colour shampoos are non-oxidative products — they contain neither H₂O₂ nor oxidative precursors. Instead, pigments (synthetic or plant-based, e.g. henna, indigo) settle on the surface of the hair's cuticle through electrostatic charges or adhesion. They do not penetrate into the cortex, which is why:

• the colour is far less durable — it usually lasts for 2–8 washes,
• they do not lighten hair (no reaction with melanins),
• they can refresh colour after dyeing or slightly alter the shade,
• they are much gentler on the hair structure.

You'll find the full range of such products in the colour shampoo category.

Longevity — dye wins, but at a price

When it comes to colour longevity, oxidative dyes have no competition. The colour lasts from 4 to 8 weeks, and with permanent dyes practically until your roots grow out. Colour shampoos need to be used every few washes to maintain the intensity of the shade — a plus for anyone who likes to experiment with colour without a long-term commitment.

Effect on hair structure

This is where the difference is fundamental. Oxidative dyes, especially with repeated use, can lead to:

• lifting and damage to the cuticle,
• loss of elasticity and increased hair porosity,
• dryness — particularly at high H₂O₂ concentrations (12%, 40 vol.),
• an increased risk of contact allergy (p-phenylenediamine (PPD), resorcinol are listed as potentially sensitising substances in CosIng).

EU Regulation 1223/2009 requires dye manufacturers to include allergy warnings and to recommend a safety test before each use (patch test). Colour shampoos are safer in this respect — they cause allergic reactions less often, although synthetic pigments can also be sensitising.

When to choose dye and when colour shampoo?

The answer depends on several factors:

1. Grey coverage: Only oxidative dye effectively covers grey hair. Colour shampoos give it a tint, but don't conceal it permanently.
2. Hair condition: Hair that is badly damaged, dry or has undergone chemical treatments (perm, keratin straightening) is less resistant to further oxidation. In that case, colour shampoo is a sensible solution for refreshing the colour between dye jobs.
3. Desired result: A radical colour change or going to a lighter shade — only dye will do. A subtle shade adjustment or extending the life of your colour — colour shampoo is enough.
4. Allergy history: People with a contact allergy to PPD should absolutely avoid oxidative dyes and consider plant-based alternatives or shampoos with direct pigments.

What to look for in the formulation?

For dyes, check the H₂O₂ concentration and whether the product contains p-phenylenediamine (PPD) or resorcinol — both substances are flagged in the PurScore Ingredient Encyclopaedia with a full safety profile. For colour shampoos, it's worth paying attention to the presence of sulfates (SLS/SLES), which can speed up pigment wash-out, as well as silicones that build up on the hair.

Note: the information above is educational in nature and does not replace advice from a trichologist or dermatologist. In the event of an allergic reaction after colouring, consult a specialist.

Check the ingredients in your cosmetic →