Bleach Damage

What a lightener actually does to the fibre

A lightener is three things working at once. An alkaline agent — ammonia, or monoethanolamine in the low-odour formulas — raises the pH, swells the fibre and lifts the cuticle. Hydrogen peroxide supplies the oxygen. In powder lighteners, persulfate salts — ammonium, potassium and sodium persulfate — push the lift further and faster.

In alkaline conditions peroxide gives up the perhydroxyl anion, which is the species that decolours. The hydroxyl radical first oxidises melanin units to quinones; the more nucleophilic perhydroxyl anion then opens the rings, and the pigment breaks into colourless fragments that rinse away.

Everything else is collateral. Electron microscopy and redox proteomics of progressively bleached hair show peroxide reaching the cortex quickly, melanin granules degrading after even the mildest treatment, and protein leaching from cuticle and cortex alike. Oxidation goes for the sulphur-containing amino acids ahead of everything else — precisely the part a perm depends on.

From cystine to cysteic acid, and why it is a dead end

A disulphide bond is a cystine residue: two cysteine side chains joined sulphur to sulphur. Oxidation does not remove it in one move. It walks it through stages, and each stage has a proper name.

On the intact bond, the oxidant adds an oxygen to one sulphur to give cystine monoxide, a thiosulfinate, then a second to give cystine dioxide, a thiosulfonate. Infrared spectroscopy detects both in bleached hair, along with a Bunte salt — an S-sulfocysteine — where sulfite or persulfate is present. None of them is stable, and the sulphur-sulphur link breaks.

That leaves a free thiol, which oxidises through three steps of its own: cysteine sulfenic acid, then cysteine sulfinic acid, then cysteine sulfonic acid, which is cysteic acid.

In living tissue the sulfenic stage is reversible, and enzyme systems exist to pull it back. Hair is dead keratinised tissue with no metabolism, so nothing pulls anything back.

Cysteic acid is measured by its infrared and Raman band at about 1040 cm−1. It climbs with each successive bleach as the disulfide signal falls, and tensile strength falls with it. Sulphur is the main casualty but not the only one: proline, threonine, arginine, lysine and the peptide bonds are oxidised too.

Which governs everything else here. A perm lotion is a reducing agent, and its entire job is to find a disulphide bond and split it into two thiols so the hair can be reshaped and rejoined. At a cysteic acid site there is nothing to find: the sulphur is unpaired, carrying three oxygens as a sulfonate group, and a reducing agent neither strips those oxygens off nor manufactures a partner. That is the mechanism under everything else on this page, and it is why the default answer is no.

It also explains the softness under the fingers — a sulfonate group is charged and water-loving, so hair carrying many of them swells and softens further in water. And it explains why the damage never lifts. Cysteic acid is something the hair has been through, not a state it can be treated out of. The affected length grows down at about half an inch a month, a little over a centimetre, and is cut off.

18-MEA, and why bleached ends drink lotion

Healthy hair is waterproofed by a bound lipid layer whose principal component is 18-MEA, 18-methyleicosanoic acid. It is covalently attached to the protein beneath through thioester linkages, and alkaline oxidative conditions cleave those linkages. Bleach is alkaline oxidative conditions by definition.

Surface analysis of bleached hair finds the water-repellent layer partly gone, with hydrophilic sulfonate groups facing outward in its place — the same cysteic acid, now at the surface. The chemistry is inverted, not merely worn away.

Damage does not make hair harder to process. It makes it dangerously easy.

Bleached ends do not resist perm lotion. They take it in several times faster than virgin hair and finish long before the root has started. This is the mechanism underneath the default answer on the cornerstone diagnostic page, and it is the reason your stylist can look at dry hair that feels rough and tell you it will over-process rather than under-process. Dryness and resistance are not the same thing. The porosity guide covers the reading in full.

How it presents, and how it is tested

Dry, the signs are suggestive rather than conclusive: a matte surface that catches a comb at the mid-lengths, ends that mesh instead of separating, the small white nodes clinicians call trichorrhexis nodosa, and short broken hairs along a parting where foils have been overlapped year on year. Wet is where the diagnosis is made, and there are four tests.

1. History. Ask for dates, and ask about lightener specifically — bleach, highlights, foils, balayage, bleach bath, colour remover, home kit — because clients answer the question they were asked, and “have you coloured your hair” is not it.
2. Wet elasticity, which decides it. A wet strand held between the fingers of both hands and stretched slowly. Healthy hair stretches appreciably and springs back; bleached hair stretches and stays stretched. Test root, mid-length and ends. The answer differs at each, and the ends govern.
3. Porosity. A speed reading rather than a verdict. It says how fast the chemical will go in; elasticity says whether there is anything for it to work with.
4. The strand test. The only one that answers the actual question: a hidden section, real lotion at real strength, timed and neutralised properly, assessed wet and dry. On bleached hair it softens early, will not hold the shape of the rod, and can be drawn apart between two fingers.

Where the line sits

Usually no — and usually is doing real work in that sentence. Bleaching oxidises the sulphur that holds hair together into a form no neutraliser can rebuild, so most bleached or highlighted hair takes a curl that drops out within weeks while the hair pays for it. That is the default and the default is no. But it is a judgement made on the hair in front of me — how much lightener, how long ago, how much has grown out, what condition the rest is in — and occasionally, in the right hands and at the right strength, it is possible. Assume no, and come and let me look rather than deciding from a page.

The last line is a different chemistry and a different mechanism, set out on perm versus relaxer. It is on this table because it comes up in the same conversation.

“It was only a few foils”

This is the conversation the page exists for, and it deserves a straight answer rather than a flat no.

First, arithmetic. A few foils every three months for four years is sixteen applications, and because foils are taken from the same weave in the same partings, most land on hair already lightened. The client is describing one appointment. The strand has been through sixteen.

The second is the rod, and it is the argument that holds. A wound rod carries a few hundred hairs, with lightened strands threaded through alongside virgin ones, and the lotion cannot be told which is which. Having lost their 18-MEA, the lightened hairs absorb several times faster and finish while the virgin ones are still working. No timing serves both: shorten the process and the virgin hair never takes, run it long enough and the highlights come away on the rod at the unwind.

So the answer is not that your hair is ruined. It is that the highlights cannot be isolated, and a perm has to work for the whole rod or it does not go on.

That argument is why fineness on its own does not open a window: the rod does not care how fine they are. If a window opens at all it is opened by the whole picture — how much lightener, how long ago, how much has grown out, what the rest of the hair does wet — and that is a judgement I make with the hair in my hands rather than one you can take off a page.

Bond builders, honestly

The best-known active is bis-aminopropyl diglycol dimaleate, the molecule in the Olaplex system: a maleate diester, and an alpha,beta-unsaturated Michael acceptor. The claimed mechanism is that its two maleate sites accept free thiol groups, capturing them before oxidation carries them on to cysteic acid, and bridging two so the pair behaves like a cross-link. Shikimic acid sits in the same patent family. Both act on free thiols, which is why their moment is during and immediately after a service — and a bridge made through a maleate linker is not a disulfide bond.

Independent testing is narrower than the advertising. A 2021 study assessed commercial reconstructive agents on bleached hair by infrared, Raman and scanning electron microscopy. It found clear morphological benefit — a more regular surface, better imbricated scales — alongside no increase in cortical disulfide content and no direct evidence of the proposed cross-linking.

One point of housekeeping, because the words have got tangled: a treatment sold as a bond or curl rebuilder is not a perm. Those products work on hair that already has curl, and will not put a wave into hair that has none.

What this means on the menu

What is not booked on bleached hair as a matter of course: a cold or alkaline perm, an acid or acid-balanced perm, a digital or hot perm, a volume or root-lift perm, a body wave. Ranked mild to harsh, the reducing agents run sulfite, then cysteamine and the thio-free systems, then true acid, then acid-balanced, then alkaline — and every one needs intact disulphide bonds to work with. A gentler chemical on hair without bonds is a gentler way of achieving nothing. Nothing on that list becomes the exception by being milder: if there is an exception it is in the hair, not in the bottle.

What can be booked, and what an honest salon should put in front of you instead:

Questions