Hair damage and repair

See how it works

Do this

1. 1Lighten less: fewer sessions, weaker developer (bleach strength), no overlap on bleached lengths.
2. 2Dry hair before using irons or tongs; never heat wet hair.
3. 3Use the lowest heat that works, with fewer passes.
4. 4Condition every wash and detangle wet, working from the ends upward.
5. 5If you bleach, add a bond-building treatment as a helper, not a fix.
6. 6Trim split ends; no product mends them, and splits can travel up.

The numbers behind it

• +47.6%

  Higher strength of bleached fibres after one bond-builder treatment. Another brand gave 19.5%, not significant (3 hair bundles per group, lab).

  Martins 2024 ↗

• Up to 40%

  Drop in fibre stiffness after each bleaching treatment. Surface roughness change rose by up to 65% with repeat bleaching (lab).

  Humphry 2022 ↗

• Up to 85%

  More damage from 'ammonia-free' colours using MEA (an ammonia substitute) than from ammonia ones (Procter & Gamble lab study).

  Bailey 2014 ↗

• 56-124%

  More cycles to break for chemically treated hair after a citric acid treatment (L'Oreal lab study on cut hair).

  Zhang 2025 ↗

For your hair

• Bleached or relaxed hair

  Weakest when wet. Condition before handling and use the least heat.

• Curly and coily hair

  Bleach weakens every hair type. Curls also snag easily, so condition well and detangle wet.

Myths to ignore

• Myth Bond builders re-link the broken bonds in your hair.

  Truth An independent test found no extra disulfide (sulfur-to-sulfur) bonds and no direct sign of the claimed reaction. The hair surface did look more regular.

  Di 2021 ↗

• Myth Oils and masks repair split ends.

  Truth In bleached or weak hair, splits start inside the fibre and can run far up it (small lab test). Products may hide them; only cutting removes them.

  Taylor 2024 ↗

• Myth Ammonia-free colour is gentle.

  Truth In one lab study, colours with MEA instead of ammonia caused up to 85% more damage at the highest MEA levels.

  Bailey 2014 ↗

• Myth Protein treatments rebuild hair.

  Truth Hydrolysed keratin (broken-down wool protein) coats hair and partly enters it. Treated hair kept its strength after UV while untreated lost 14.32%. That is UV protection, not rebuilding.

  Fan 2025 ↗

Made for this

• Repair Mask Weekly reinforcement for bleached, heat-styled or brittle hair
• Leave-in Heat Shield Leave-in mist to use before blow-drying or hot tools
• Pre-wash Oil Oil before the wash, to help limit wash damage
• Rich Conditioner Deep slip and softness for curly, coily and dry hair

Go deeper

• Hair damage: what it is and where it comes fromDamage is cumulative and cannot be biologically healed, and chemical treatments, heat, sun, water and grooming each add to it.
• Bleach and colour damageBleaching and permanent dyeing chemically damage the hair fibre in every hair type, and most of that damage cannot be undone.
• Bond builders (Olaplex, K18, maleic acid, "acidic bonding")Bond builder is a marketing label for four unrelated chemistries; all have lab results on cut hair and none has a trial on real heads.
• Split ends and trimmingSplit ends cannot be repaired, only smoothed over or cut off, and trimming preserves length by stopping splits travelling up the strand.
• Proteins and hairHydrolysed proteins can modestly strengthen damaged hair in the lab, but the popular protein-moisture balance rule has never been tested.
• Oils and hairOils coat hair and some enter it, which can cut damage from washing, but they do not repair split ends or add moisture.
• Heat damage and heat protectantsHeat on wet hair is the clearest harm, and there is little independent evidence that retail heat-protectant sprays work.