Hair salon in Olbia · Total Look
The science of hair colour
Permanent colour doesn't deposit a ready-made pigment: it builds it inside the hair through oxidation. Developer is measured in volumes (10 vol = 3%, 40 vol = 12%), bleach switches melanin off irreversibly, and in Europe every dye is governed by EC Regulation 1223/2009. Here is the chemistry behind every colour service.
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How permanent colour works
Permanent dyes are mixed at application: one part contains hydrogen peroxide, the other colourless dye precursors. Oxidation transforms the precursor (classically para-phenylenediamine, PPD — used for over 150 years), which reacts with "couplers" to form large coloured molecules trapped inside the hair's cortex. Ammonia opens the cuticle; its "ammonia-free" substitute (ethanolamine) is gentler but lifts less and tends to wash out rather than grow out.
Developer volumes
"Volume" is simply hydrogen peroxide concentration: 10 vol = 3%, 20 vol = 6%, 30 vol = 9%, 40 vol = 12%. More volume means more lift: roughly 1–2 levels with 20 vol, ~3 with 30 vol, 4–5 with 40 vol. That's why a colourist chooses developer by target result, not "the strongest available".
Melanin and bleaching
Natural colour is the ratio of two pigments: eumelanin (brown-black) and pheomelanin (red-blond). Bleach oxidises melanin irreversibly — the molecule stays in the hair but turns colourless. Eumelanin breaks down faster than pheomelanin, which is why dark hair always passes through orange and yellow on the way to blond.
Safety: allergies and patch testing
PPD is the leading hair-dye allergen (positive reactions in ~4% of European patch tests). It is a delayed type-IV reaction — which is why manufacturers recommend a skin test 48 hours before colouring. In Europe, EC Regulation 1223/2009 and the SCCS scientific opinions set the limits — for PPD a 2% on-head maximum. During pregnancy, ACOG considers hair dye generally safe because scalp absorption is minimal; many sources still suggest waiting out the first trimester as a precaution.
Why colour fades
The two main factors are washing (surfactants progressively pull dye molecules out) and UV light, which acts like a slow bleach. Bleached hair is more porous and loses colour faster — which is why colour-treated hair needs dedicated aftercare and periodic toning.
Sources
- Compound Interest — The Chemistry of Permanent Hair Dyes
- EUR-Lex — Regulation (EC) No 1223/2009 on cosmetic products
- European Commission — Scientific Committee on Consumer Safety (SCCS)
- "Para-phenylenediamine allergy: current perspectives", peer-reviewed (PMC)
- ACOG — Is it safe to dye my hair during pregnancy?
- Wella Professionals — Semi vs demi-permanent colour
Last updated: June 2026