Correction

Purple Shampoo Does Not Remove Brass. It Covers It.

The claim

“Purple shampoo strips the yellow out of bleached blonde hair.”

The short answer

Lightening does not remove warmth, it exposes it. A violet shampoo deposits a direct dye that sits on the fibre and washes out; it never removes the yellow underneath. Only further lifting or an oxidative toner changes the pigment itself.

Evidence status

Settled

The Cosmetic Record · Published 2026-08-06 · Last checked 2026-08-06 · 10 sources · Corrections: none

1. Where the yellow comes from: what lightening leaves behind

The International Agency for Research on Cancer’s 1993 survey of hairdressing exposures states that “all of the bleaching methods used currently are oxidation processes”, that hydrogen peroxide is the commonest oxidant, “used usually as a 6 or 9% solution or, rarely, as a 12% solution”, and, describing permanent dyes, that hydrogen peroxide “is an excellent decolorizing agent for melanin, the hair’s natural colouring matter”.²

Decolorising melanin is not a switch. A 2017 study in Free Radical Biology and Medicine separated the two oxidising species alkaline peroxide supplies. On soluble Sepia melanin, the hydroxyl radical and the hydroperoxide ion each bleached melanin on their own, and with both present bleaching “is increased dramatically in both rate and extent”; on melanosomes isolated from human hair, hydroxyl radical generated in the surrounding solution “does not contribute significantly to bleaching”. The authors proposed that the radical pre-oxidises melanin units to o-quinones so that the more nucleophilic hydroperoxide ion can open the rings.³ That is a pigment dismantled in stages, and the colour a fibre shows at any moment is the part not yet dismantled. Nothing yellow is being added.

The far end has been photographed: electron microscopy of excessively bleached hair found torn cuticle scales, fissures along the exposed cortex, and pores where melanin granules had dissolved, with no granules detected at all.⁵ A redox proteomics study reported “extensive melanin granule degradation… after the mildest bleach treatment”.⁴ So the brass is not a film resting on the hair. It is the hair’s own pigment part-way through being destroyed, and no wash step reaches it.

2. Two different jobs — taking pigment out, and putting pigment on

Two operations get discussed as though they were one. The subtractive operation degrades melanin by oxidation; it is the only thing that reduces the quantity of warm pigment in the fibre. The additive operation puts a coloured molecule onto or into the fibre, which changes what you see without changing what is underneath.

A preformed dye cannot do the first job, and the IARC monograph says so flatly: “because the dyes in semipermanent hair colours are preformed and do not require added oxidant, such products cannot lighten the natural hair colour.”² That sentence is the whole correction. It is also why the subtractive route has a price the additive route does not: peroxide treatments “quickly access the cortex, causing untargeted oxidative damage across the fibre in addition to the desired loss of melanin”, with cortical intermediate filaments oxidised at their cystine disulphide bonds.⁴ In the European Union the tool is capped: Annex III entry 12 permits hydrogen peroxide and compounds releasing it in hair products at 12 % of H₂O₂ (40 volumes), present or released.¹ That ceiling is the reason the lift a box promises has a hard limit, whatever the number on the front of it says — see There Is No Standard Behind the Hair-Colour Number Chart.

3. What is actually in a violet shampoo

Read the INCI list and the violet is a named direct dye. Annex III of Regulation (EC) No 1223/2009 — the restricted-substances list — clears several violets by name for exactly this job, each with its own ceiling. Acid Violet 43 is reference number 291 (CAS 4430-18-6, EC 224-618-7), permitted as a “hair dye substance in non-oxidative hair dye products” at a maximum of 0,5 %; Disperse Violet 1 is entry 265 on the same condition at 0,5 %; HC Violet No 2 is entry 224 at 2,0 %; and Basic Violet 2 (CI 42520) is entry 278, capped at 0,5 % in non-oxidative products and at 1,0 % in the mixture applied to hair under oxidative conditions.¹ Every one of those is a ceiling on a deposit, not on a lift.

The annex a violet shampoo is judged against is not the colourant annex most people would guess.

… cosmetic products shall not contain … (c) colorants (i) colorants other than those listed in Annex IV …, except for hair colouring products referred to in paragraph 2; … 2. Subject to a decision of the Commission to extend the scope of Annex IV to hair colouring products, such products shall not contain colorants intended to colour the hair, other than those listed in Annex IV …

Acid Violet 43 sits in Annex IV too — entry 90, colour index 60730, “not to be used in products applied on mucous membranes” — but Article 14 excepts hair colouring products from that list, so the operative limit for a toning shampoo is the Annex III hair-dye entry.¹

“Semi-permanent” is not a synonym for “unregulated”. Annex II, the prohibited list, carries four consecutive direct dyes at entries 1236 to 1239 — HC Yellow No 11, HC Orange No 3, HC Green No 1, HC Red No 8 and its salts — and, unlike entries 1230 to 1233 just above them, none of the four carries the qualifier “when used as a substance in hair dye products”. They are prohibited in any cosmetic product at all.¹

Brazil splits the same way. Article 9 of ANVISA’s RDC 628/2022 says its list of permitted colourants “não inclui as substâncias corantes destinadas exclusivamente a tingir os cabelos” — does not include colourants intended exclusively to dye hair.⁸ And Brazil does not leave a violet shampoo to be placed by inference from a list. Since December 2024 the operative definition of a hair dye names the toning shampoo itself:⁷

XXXIV - tintura de cabelo temporária, progressiva ou permanente: produto para tingir os cabelos, incluindo xampu e enxaguatório capilar tonalizante ou matizador. Maquiagem capilar não está incluída nesta categoria.

So a violet shampoo is not a shampoo that happens to tint. In Brazilian law it is a hair dye that happens to lather — and the two sit in different halves of Anexo I. Plain “Xampu” is item 70 of the Grau 1 list, with “Xampu condicionador” at item 71; “Tintura capilar temporária, progressiva ou permanente” is item 45 of the Grau 2 list, filed there beside “Clareador ou descolorante para cabelos e/ou pelos do corpo” at item 9.⁷ The regulator has already decided which family a violet shampoo belongs to, and it is not the cleansing one.

4. Why the effect washes out, and why more of it is not more permanent

No reaction fixes the dye. The IARC monograph describes temporary colourants as water-soluble acid or basic dyes of the kind used for wool, “which have a molecular size too great to penetrate the cortex of the hair”, so “the dye is deposited on the surface, from which it is easily removed by washing”; semi-permanents it defines as products that “last through 6–12 washings and do not involve the use of an oxidizing agent in colour development”, their wash-fastness coming from dyes small enough to enter the cortex.² A violet shampoo lives between those two descriptions, and neither of them is permanent.

That is also why doubling the dose does not buy durability. The thing that ends the effect is the next wash, and the ceiling on what may be deposited is legal as well as physical — 0,5 % for Acid Violet 43 in a non-oxidative hair dye product in the EU.¹ Leaving it on longer changes how much dye goes on. It does not change what removes it.

5. What a toner or a demi-permanent does that a shampoo cannot

An oxidative toner is doing both jobs at once, and that is the entire difference. In oxidative dyeing the colour does not exist in the bottle: precursors penetrate the fibre and react with hydrogen peroxide to form indo dyes in place, and because the same peroxide is decolorising melanin at the same time, manufacturers “can balance the amounts of hydrogen peroxide and of dye precursors in such a way as to produce lightening, darkening or matching of the natural colour of the hair”.² A shampoo has no oxidant and no precursors, so it has no access to that balance.

Published developer strengths for the gentler oxidative products are thin. A 2015 review in the International Journal of Trichology puts demi-permanent products at 2% hydrogen peroxide against 6% for permanent, and their colour at “10–15 shampoos, or even earlier”.⁶ Neither figure carries a primary measurement, and that review also describes demi-permanents as not reaching the cortex, which is not how the trade uses the word. The only number with a document behind it is the regulatory ceiling.¹

Because these products act on the fibre, Brazil requires them to say so on the pack:

II - agentes clareadores de cabelos e tinturas capilares: a) “CUIDADO. Pode causar irritação na pele ou reação alérgica. Antes de usar, fazer a prova de toque” (descrever); b) “Em caso de contato com os olhos, lavar com água em abundância”; c) “Manter fora do alcance das crianças”; d) “Não aplicar se o couro cabeludo estiver irritado ou lesionado”; e e) “Não usar nos cílios”.

6. Colour removers: what they undo and what they cannot

There are two documented routes back. “In order to remove permanent and semi-permanent hair colourings,” the IARC monograph records, “hairdressers use reducing agents (sodium hydrosulfite or sodium or zinc formaldehyde sulfoxylate dissolved just before use in acidified water) or high-strength oxidants such as those mentioned above” — that is, the same peroxide and persulfate chemistry used for bleaching.² One route reduces a formed dye; the other oxidises it away.

Neither route puts melanin back. The electron microscopy is unambiguous that heavy bleaching leaves a cortex with no melanin granules in it,⁵ and no cosmetic regenerates them. So stripping a toner off does not return the hair to where it started; it returns it to whatever stage the lift reached, which is the warm stage the toner was covering. The remover undoes the deposit. It cannot undo the lift.