13 Hair Colour Myths Checked Against the Evidence

The headline finding is that developer strength sets lift, not grey coverage or how long colour lasts, and several of these myths give the developer, or the alkaliser, a job that belongs to the dye. Of the 13 beliefs checked, seven are false or mostly false, one isn't supported, two are unproven, one is half true, one is true only with a catch, and the cancer question splits: not shown for clients, a small and debated signal for hairdressers.

Each myth gets a verdict, the evidence with a sense of scale, what to do at the chair, and a link to the deeper article where there is one.

"A higher-volume developer gives better grey coverage"

Mostly false.

Developer strength sets lift, not deposit. A higher volume lifts more of the client's remaining pigment; it doesn't push more dye in. Wella's Koleston Perfect sheet puts grey coverage at 6% (20 vol), with 9% and 12% for two and three levels of lift. IGORA ROYAL Absolutes, built for mature hair, mixes with 9% as standard but drops to 6% "for pure colour deposit on over 90% white hair".

At the chair: on a resistant root, change the shade or the timing before you change the bottle. Our Life Color Plus grey protocol (our guidance, not a FarmaVita instruction) keeps 20 volume. Up to 50% white, it uses the desired shade alone at 1:1.5 with five extra minutes. At 50–100% white, it uses half desired shade and half natural at the same depth, mixed 1:1, for 45 minutes. Deeper: the grey coverage formula and the developer decision guide.

"Mix 20 and 40 vol and you've got 30 vol"

True, with a catch.

On paper, equal parts of 6% and 12% hydrogen peroxide work out at 9%, the strength sold as 30 volume. The catch is that the sum assumes both bottles still hold their labelled strength and are measured accurately, and no published data show how fast cream developer loses strength. For example, if the 40 vol had lost a tenth of its strength, the blend would land nearer 8.4%.

At the chair: if the formula calls for 30 vol, use a 30 vol bottle. FarmaVita's Life Color Plus directions call for 20, 30 or 40 volume, and each is made as its own bottle, so there is no need to blend to reach one. Deeper: can you mix developer volumes?

"You can keep mixed colour for the next client"

False.

Mixed colour is a reaction in progress, not a stock product. In a Cosmetics Europe lab test, a quarter to a third of one precursor and coupler pair was still unreacted at 30 minutes and dye was still forming. Wella's US Welloxon Perfect instructions say: "USE COLORANT MIXTURE IMMEDIATELY AND DISCARD ANY UNUSED MIXTURE". The verdict rests on that and the chemistry, not a storage test.

At the chair: mix per client, at the moment of application, and only as much as the head needs. Life Color Plus mixes 50 ml of colour to 75 ml of developer as standard, so a measured half tube is easy to make up. Deeper: cutting colour waste.

"Ammonia-free colour is gentler on the hair"

Not supported.

It's easy to see why people believe it: ammonia smells sharp and stings the eyes, so leaving it out must be kinder. Part of that holds. Ammonia is a gas at room temperature; its usual replacement, MEA, boils at 170 °C, so far less of it reaches the air, and ammonia is a known airway irritant in salons. But two industry-run lab studies found high-dose MEA damaged hair more, not less. Demi-permanents are gentler because they use weaker peroxide, and they won't lighten natural colour.

At the chair: ventilate your mixing area, and choose by the lift you need rather than the label. Deeper: ammonia vs ammonia-free hair colour.

"PPD-free colour is safe for a client who reacted to PPD"

False.

"PPD-free" colours can swap PPD for PTD (toluene-2,5-diamine), as the range in the ASA's February 2025 ruling did, and PTD is PPD with one extra methyl group. Cross-reaction between the two is common, and more common in people with stronger PPD patch-test reactions. Even the newer ME-PPD ("ME+") cross-reacted in roughly 30% to nearly 90% of PPD-allergic people, depending on the trial (all manufacturer-funded trials).

At the chair: a passed pretest isn't clearance either: in one ME-PPD tolerance study, 9 of 38 PPD- or PTD-allergic people who passed a 45-minute pretest still reacted on full use. Treat a past PPD reaction as a stop for oxidative colour, whatever the box says. Life Color Plus is not marketed as PPD-free, and an official FarmaVita chart (2015) carries the regulatory benzenediamines and toluenediamines warning for the range. Deeper: are "PPD-free" claims real?

"You only need to patch test new clients"

False.

Manufacturers ask for an allergy alert test before every colour service, not only the first. Matrix's US colour manual requires it 48 hours before each application, "even if you have previously applied this product or another colorant on your client". Wella's Koleston Perfect fact sheet says: "Always perform an allergy alert test 48hr before each coloration". EU scientists class PPD, a common colour ingredient, as an extreme sensitiser.

At the chair: the Life Color Plus product listing says: "Always conduct a patch test 48 hours before applying the color". Record each result on the client card. A client who has reacted to any colour, from any brand, is a stop, not a re-test: the legally required label warning says "Do not colour your hair if: … you have ever experienced any reaction after colouring your hair". Deeper: the first-time client guide.

"Hair dye causes cancer"

Not shown for clients; a small, debated signal for hairdressers.

Clients hear "probably carcinogenic" and see straightener headlines, so "dye causes cancer" sounds settled. IARC's Group 2A covers occupational exposure as a hairdresser, not clients colouring their hair (personal use is "not classifiable"), and its groups rank strength of evidence, not size of risk. The headline study linked straighteners to uterine cancer; permanent dye showed no link. Older US dyes did contain 2,4-diaminoanisole, which caused tumours in animals, and it was dropped before 1980; whether the hairdresser bladder-cancer signal has faded since is still an open question. Your dose is low but repeated; in one study it built up over a week of reused gloves.

That hairdresser signal is bladder cancer, at about 1.2 to 1.6 times baseline in the European studies of male hairdressers behind IARC's 1993 rating, reaffirmed in 2010. In 1993 IARC noted that the three case-control studies that adjusted for smoking found no excess. But a 2010 pooled analysis of 42 studies found almost the same excess with smoking adjustment (1.35) as without (1.33).

In size terms, a UK estimate attributes about 0.16% of British bladder cancers to hairdressing, roughly 15 registrations a year (2004 baseline), with a range running from zero to about 0.6%. That figure counts some 728,000 people who worked as hairdressers or barbers over several decades, not the workforce in one year, and its input risk was not adjusted for smoking.

At the chair: glove up for mixing, applying, rinsing and cutting freshly coloured hair, and never reuse disposables. If a client asks: "For clients, IARC can't classify it; the largest study found no link with most cancers."

"Permanent colour doesn't fade"

False.

Permanent colour is built inside the hair, but built isn't fixed: in lab tests on commercial permanent auburn dyes, both light and shampooing changed the colour, and the two together changed it significantly more than either alone. The worst-performing dyes moved about 4 to 6 ΔE units (the lab measure of colour change) after ten shampoos, and 14 to 16 with 32 hours of simulated sunlight plus four shampoos.

At the chair: ask about wash frequency and sun at consultation, and brief lightened and white-haired clients first: in the same tests their colour changed much more than on brown hair. Deeper: does permanent hair colour fade?

"Reds fade fastest because red dye molecules are bigger"

Half true: right worry, wrong reason.

You'll hear that reds fade because their molecules are too big to get in. Brands repeat it; no study we found does. The size story fits direct dyes, which shampoo out, not reds as such. Permanent colour long lacked a true red coupler, so makers added red direct dyes, which Clairol's 1994 patent says could turn "drab brown" within two shampoos, especially after perms or relaxers. Henkel called red-range wash fastness improvable as late as 2018. Some shades still list direct dyes such as HC Red No. 3. In one lab test, washing plus light faded auburn shades most, worst on bleached or white hair.

At the chair: cut both washing and light for red and copper clients, especially on bleached or white hair, and check a red shade's INCI for direct dyes. The EU's SCCS calls HC Red No. 3 an "extreme contact sensitiser" in animal testing, one more reason the patch test matters. Deeper: refreshing mid-lengths and ends.

"Sulphate-free shampoo stops permanent colour fading"

Unproven.

Clients swear by sulphate-free, and the logic sounds right: sulphates strip oil, so surely they strip colour. The evidence is thinner. In skin patch tests SLS irritated far more than SLES, also a sulphate, so "sulphate" isn't one thing. We found no published study comparing sulphate and sulphate-free shampoo on permanent colour. A polymer maker's own study says oxidative colour fades mainly as dye dissolves into wash water, and the protection data it reports is for conditioning polymers. Two salon "sulphate-free" colour shampoos we checked list olefin sulfonate, another anionic cleanser, second.

At the chair: read the ingredient list, not the "sulphate-free" claim, and don't promise any shampoo stops fade. Deeper: does permanent hair colour fade?

"Purple shampoo fixes brassiness for good"

False.

Purple shampoo is a violet direct dye, usually Acid Violet 43, in an oxidant-free shampoo base. It deposits violet over the yellow rather than removing its cause, and its semi-permanent dye family washes out. Heat and light keep yellowing the hair, and on lightened hair leftover pigment is the usual explanation. In an independent German test, 6 of 20 silver shampoos made no perceptible change to yellowed grey hair.

At the chair: position purple shampoo as maintenance between visits. A salon toner neutralises for longer, but if the brass is under-lifted pigment it will come back as the toner fades; the lasting fix is lifting further at a later appointment. Deeper: neutralising brass and green bands and Life Color Plus correctors and toners.

"Colour remover is just a weaker bleach"

False.

They run opposite reactions. A colour remover reduces: sulfur-based reducing agents break down synthetic oxidative dye. Bleach oxidises, and melanin breakdown needs an oxidant, working best at alkaline pH. On its documented chemistry, a remover has no route to the client's own pigment. L'Oréal's patent attributes colour that comes back to leftover dye precursor re-reacting when an oxidation-based remover's own oxidiser reaches it.

At the chair: after a true colour remover, read what's underneath as the client's own pigment as the original permanent colour left it: usually lighter and warmer than their natural depth, because permanent colour lifts as it deposits. Remover takes out the artificial dye; it doesn't put back pigment the colour service already lifted. After a bleach bath, treat the hair as lightened further still. Deeper: colour remover vs bleach bath and underlying pigment explained.

"Bond builders make colouring damage-free"

Unproven.

It's easy to see why people believe it: bleach turns many of the disulphide bonds that give hair its strength into cysteic acid, so a product sold as "rebuilding bonds" sounds like it cancels the damage. The evidence is narrower. In one university test, Olaplex No.0 applied to already-bleached hair raised tensile strength by 47.6%, but on three tresses, with an effect the authors call short-term; another found maleate-based repair agents added no disulphide bonds in the cortex, where the first reported more. Neither measured prevention during the service.

At the chair: treat bond builders as a top-up, not insurance, and follow the brand's current dosing and developer instructions.

Related: The Developer Decision: 10, 20, 30 or 40 Volume, Are "PPD-Free" Hair Colour Claims Real? The ASA Ruling and the Chemistry Behind It and Does Permanent Hair Colour Fade? What the Research Shows.

Colour chemistry: questions colourists ask.
See also: 1.9% developer explained · Can you mix developers across brands? · Does porosity affect hair colour?
Shades: Life Color Plus tubes, £3.49

Sources: IARC Monographs Volumes 57 (1993) and 99 (2010) and IARC's Monographs Q&A; the US National Cancer Institute's "Hair Dyes and Cancer Risk" fact sheet; Chang et al. (2022, JNCI); the US NTP Report on Carcinogens entry for 2,4-diaminoanisole sulfate; Takkouche et al. (2009, International Journal of Epidemiology); Czene et al. (2003, International Journal of Cancer); Gube et al. (2011) and Geens et al. (2016, Occupational and Environmental Medicine) on hairdressers' exposure; and IARC's classification of PPD (Volume 16 and Supplement 7, via PubChem); Zhang et al. (2020, BMJ), the Nurses' Health Study; Harling et al. (2010, Occupational and Environmental Medicine); Brown, Slack & Rushton (2012, British Journal of Cancer); UK-retained Regulation (EC) 1223/2009, Annex III; the ASA ruling on Instituto Naturvita S.L. t/a Natur Vital (12 Feb 2025); the SCCS opinions on toluene-2,5-diamine and p-phenylenediamine; Vogel et al. (2017) and the published ME-PPD cross-reaction and tolerance trials in Contact Dermatitis and the British Journal of Dermatology; Ali et al. (2018, ACS Omega); PubChem entries for ammonia and ethanolamine; Kezic et al. (2022, IJERPH) and Mounier-Geyssant et al. (2006, Environmental Health) on salon air; Bailey, Zhang & Murphy (2014, J Cosmet Sci); Locke & Jachowicz (2005) and Zhou et al. (2009), both in the Journal of Cosmetic Science; ÖKO-TEST's silver shampoo test; He et al. (2023, Frontiers in Medicine); Clairol's US Patent 5,344,463 and Henkel's US 11,497,699 B2; the SCCS opinion on HC Red No. 3 (SCCS/1293/10); Löffler & Happle (2003, Contact Dermatitis); Gavazzoni Dias (2015, International Journal of Trichology); Grosvenor et al. (2018, International Journal of Cosmetic Science); the Olaplex professional manual; Hawkes et al. (2026, International Journal of Cosmetic Science); Smith et al. (2017) and Korytowski & Sarna (1990) on melanin bleaching; Martins et al. (2024, Cosmetics); Di Foggia et al. (2021, International Journal of Biological Macromolecules); the Goebel/Cosmetics Europe "Chemistry of Hair Coloring" presentation (2017); patent application US 2002/0124329 (Pratt), US Patent 12,458,576 (L'Oréal) and P&G's EP 2 476 405; Wella's Koleston Perfect fact sheet (UK) and US Welloxon Perfect product pages; Schwarzkopf Professional's IGORA ROYAL Technical Manual (GB edition); the Matrix colour manual (US); FarmaVita's Life Color Plus directions and 2015 shade chart; and the Life Color Plus product listing. Competitor information comes from those manufacturers' own published material; always work to the instructions supplied with the product you are using.