Does Coloring Damage Hair? What Dye and Perms Do to Each Strand

Does dyeing your hair damage it?

Permanent color does, a little more with every appointment that reaches the same lengths.

Start with the age of your ends. Scalp hair grows about 1 to 1.3 cm (roughly half an inch) a month, slower for some people, so the tips of hair 30 cm (12 inches) long are about two to two and a half years old. Color every six weeks, pulling the color through to the ends each time, and those tips have been processed close to twenty times. The hair nearest your scalp has been through it once at most.

Permanent (oxidation) color, about 80% of the hair dye sold, works at an alkaline pH, typically 8 to 10 (da França 2015; Robbins 2012). The alkali, ammonia or ethanolamine, swells the hair so small dye precursors can get in. Hydrogen peroxide oxidizes them, and they react inside the hair, mostly in the outer cortex, to form dyes "too large to slip out" (Ahn and Lee 2002). The same peroxide lightens your natural pigment, even for a small shift lighter, and the hair chemist Clarence Robbins notes that this bleaching "can produce damage to the hair proteins and lipids."

The first loss is the slick surface. Ammonia and ethanolamine remove the water-repellent surface lipid (18-MEA), so the surface starts to attract water and friction rises; washing and wear finish the job (Gavazzoni Dias 2015; Tokunaga 2019). In one lab test of a blond oxidative dye, colored hair lost more protein and took more work to comb, wet and dry, while its breaking strength did not differ significantly from untreated hair (da Gama 2018). In that test, the damage showed up at the surface, as harder combing, not as a weaker fiber.

None of this undoes itself. The shaft is not living tissue and cannot repair itself, so processed length stays until it is cut (Osório and Tosti 2011). Treatments also compound. "Treatment combinations are oftentimes more damaging to hair than one might expect," Robbins writes, and hair lightened or permed before reacts faster to the next chemistry. For what disulfide bonds are, see what hair bonds are.

How can you tell if coloring has damaged your hair?

Count what the oldest part of each strand has been through, then compare it with the newest. Your eyes are a poor guide: in a small study, women who regularly bleached, dyed or straightened their hair had significantly more shaft damage under an electron microscope than women who did not, though both groups looked alike under a light microscope (Kaliyadan 2016). Your roots are the control.

1. Date your ends. Measure a strand from scalp to tip in centimeters; at the growth rate above, that number is roughly the age of the tip in months. Count every permanent color, lightening, perm, relaxer or gloss mixed with developer since then that reached the ends, not just the roots. That is how many times your ends have been processed.
2. Feel for the change. Ends that drag between your fingers where the roots slide freely point to a worn surface layer. On permed hair, compare the mid-lengths too; in one study the tips had lost more of their surface lipid.
3. Watch the color. Damaged and lightened hair takes up and loses dye faster, so lengths that fade well before the roots, or that grabbed a semi-permanent shade darker than the regrowth, are behaving like damaged hair (Robbins 2012). More in the science of hair porosity.
4. Check wet hair after towel drying. In lab tests, hair with its surface lipid separated into fine, parallel bundles; without it, the hair formed thick, disorderly clumps (Tokunaga 2019).
5. Read the brush. Chemical damage raises friction between hairs, "leading to more tangle formation and more breakage" (Robbins 2012). Short broken pieces from the colored lengths are the thing to look for; hair breakage explains how to tell them from shed hairs.

We know of no tested scale for these checks; as a rule of thumb, the more services your ends have had and the more of signs 2 to 5 you notice, the more the order and spacing of your next service matter. Ends that snap during gentle combing, or lightened ends that feel gummy when wet, are a reason to pause chemical services and ask for a strand test first; see gummy hair.

The check counts what your ends have been through. If that count is high or the signs are adding up, it cannot tell you why your lengths behave as they do, or what to change before your next appointment, in what order. The free hair consultation works that out: it asks about your color, heat, washing and how your hair behaves, scores porosity and damage, takes about a minute, and asks for your email before it shows your Damage Profile and a matched routine. Find your Damage Profile

Which hair color is least damaging: permanent, demi or semi-permanent?

Going by the chemistry, from least to most: temporary color, semi-permanent, demi-permanent, permanent to the same or a darker shade, permanent that lightens, then bleach. We found no study comparing them all side by side; the order follows from what each one uses.

Not sure which row is yours?

If you do not know which of these your colorist uses, ask whether a developer is mixed in, and at what volume. Demi-permanent color is gentler, though it still oxidizes: it uses oxidation dyes with a weaker developer, typically does not lighten, fades after roughly 10 to 20 shampoos and covers gray less completely (Gavazzoni Dias 2015; da França 2015).

Semi-permanent color uses no peroxide, so "no 'major' chemical changes occur to the fibers," in Robbins's words, although alkaline formulas can still swell the hair.

Is ammonia-free hair color less damaging?

Not by any measurement we found. "Ammonia-free" permanent color usually swaps ammonia for ethanolamine (MEA), chosen because ammonia smells (Ali 2018), and both remove the same surface lipid (Gavazzoni Dias 2015).

The evidence on damage comes mostly from manufacturers, and they disagree. Scientists at a major hair-color company measured more damage from MEA-based colorants than from ammonia-based ones by three methods, protein loss among them (Bailey 2014).

In a lab model from Imperial College London, with co-authors from that company, an hour at 50 °C (122 °F) in a 5% MEA solution, with no peroxide or dye, weakened wet hair and stripped more cuticle; the ammonia solutions tested left wet strength unchanged and, even after nine hours, cost less protein than MEA did in one. Hot, alkali-only soaks are not a salon service (Ali 2018). A study funded by the maker of an ammonia-free dye reported improved rater-scored shine and combability in 50 women, with no comparison dye and no instrument measuring damage (Draelos 2022). "Ammonia-free" describes the smell and the alkali. It is not a measured promise of less damage, and the lab comparisons we found point the other way.

Does a perm damage your hair?

Yes. A perm breaks some of the disulfide bonds that hold keratin in shape and re-forms them around a rod. Most re-form, not all, so permed hair stays chemically changed until it is cut.

A standard perm, the "cold wave" in chemists' terms, has two steps. A thiol solution, mostly thioglycolic acid at about pH 9 to 9.5, breaks disulfide bonds while the hair is wound on rods; a mild oxidizer, usually dilute hydrogen peroxide, then re-forms bonds in the new shape. An average thioglycolate perm breaks open about 20% of the hair's cystine, the amino acid that forms those bonds. Neutralizing brings strength back toward where it was, but not fully: wet strength stays lower, while dry strength remains "virtually unchanged" (Robbins 2012).

The traces last. In one analysis, permed hair carried roughly two to four times the cysteic acid, an oxidized form of cystine, of unpermed controls, and it has higher friction and combs harder. X-ray measurements on one person's hair after a salon perm showed altered keratin structure inside the fiber, which a single shampoo and conditioner did not change (Zhang Y 2015).

As with color, the ends take the most. In one study of hair permed every two to three months, 18-MEA barely changed at mid-lengths but fell sharply at the tips, and Robbins concludes that perming has "a profound effect on reducing the abrasion resistance of hair."

Are some perms gentler than others?

The reducing agent matters. Acid perms (glyceryl monothioglycolate) and sulfite perms are milder than alkaline thioglycolate perms, and sulfite breaks fewer bonds. For straighteners that use the same chemistry, Robbins goes further: "considering only hair damage sulfite would be the preferred reducing agent." Japanese straightening adds a flat iron after the reducing step; for what hot tools add, see heat-damaged hair. At home, the American Academy of Dermatology (AAD) advises setting a timer and following the package instructions exactly.

Perm vs relaxer: what is the difference?

A perm breaks bonds and re-forms most of them; an alkaline relaxer breaks them and converts some for good. Lye and no-lye relaxers use a hydroxide, or guanidine, at about pH 12 to above 13, and Robbins calls alkaline straighteners "the most damaging of all hair straightening products." The hydroxide turns some cystine into lanthionine, a stable sulfur crosslink that "creates an irreversible situation," and the high pH removes the surface lipid. Relaxed lengths measured markedly lower in cystine in one study, and hair relaxed less often kept more of it (Khumalo 2010).

"No-lye" names the chemical, not the damage level: in lab tresses, lye and no-lye straighteners caused statistically similar protein loss and breaking force (Velasco 2022). Hydroxide relaxers and thioglycolate products are incompatible with each other and with bleached hair (Gavazzoni Dias 2015).

Can you color and perm at the same time?

No. The AAD advises one service at a time; if you want both, perm or relax first and color two weeks later. Combinations often do more damage than you would expect. In lab tresses that were dyed and then relaxed, a sodium hydroxide relaxer caused far more protein loss than the dye alone, while thioglycolate or guanidine relaxers added only a little (França-Stefoni 2015); the order the AAD recommends was not tested. On relaxed hair, one review recommends demi-permanent rather than permanent color and calls highlights or light shades "absolutely incompatible" with relaxers (Gavazzoni Dias 2015).

Is bleaching worse than dyeing?

Yes. Bleach is the strongest oxidizing step in hair color and breaks more disulfide bonds than permanent dyeing. Highlights and balayage are lightening, so they count here, and permanent color that lifts more than three shades needs higher volumes of peroxide, which the AAD says causes more damage. For what bleach does and what to do afterward, see how to repair bleach-damaged hair.

Can you dye your hair without damaging it?

Temporary and semi-permanent color come closest: no peroxide, no oxidation and no lift, so far less chemistry reaches the hair. Demi-permanent color involves some oxidation. Permanent color always includes some bleaching, because the peroxide that develops the dye also lightens natural pigment, so no version is damage-free, ammonia-free included; what you control is how much.

Is it healthier for your hair not to dye it? For the fiber, yes. Every oxidative service costs the hair it reaches something it cannot get back. Whether the color is worth that is your decision, and a reasonable one either way.

How often can you dye your hair?

No study we found sets a safe number of colorings a year. The AAD advises more time between touch-ups, especially when the air is dry, stretching to every 8 to 10 weeks or longer in winter. Touch-ups belong on new growth only (Gavazzoni Dias 2015).

The eight-week rule you hear in salons has a traceable source. In 2002, researchers at Yonsei University in South Korea followed one 26-year-old woman's hair under the electron microscope after a permanent dye. The cuticle looked worst within the first day, with jagged, detached scales. By eight weeks, the authors concluded, hair "returns to its precoloring state," and they recommended at least eight weeks between colorings (Ahn and Lee 2002).

The study sampled one person, took only the 3 to 5 cm of hair nearest the scalp, and was partly funded by a cosmetics company. Its idea of recovery also runs against the biology above. Spacing is sensible because damage adds up, not because hair recovers in between.

Your regrowth sets the practical pace. Gray at the roots after permanent color is new hair, not dye washing out, and it may start to show at four to six weeks. Overlapping new color onto previously treated hair doubles up at the junction, where relaxed hair tends to break. Faded lengths in between can be refreshed with semi-permanent color, which uses no peroxide; a demi-permanent gloss still oxidizes and counts as another service on those lengths.

What is the healthiest way to color hair?

Use the least chemistry that gets the result, only on hair that has not had it, with time between services:

1. Choose the smallest step that does the job: temporary or semi-permanent color for a change of tone, demi-permanent to refresh or blend, permanent for full gray coverage or lift.
2. Stay within three shades of your natural color where you can; the AAD notes that lightening more than three shades needs higher volumes of peroxide.
3. Put new color on new growth only, and ask your colorist to keep it off lengths already colored.
4. Book one chemical service at a time. For a perm or relaxer plus color, have the perm or relaxer first and color two weeks later. Ask for a strand test before relaxing; it is sensible to ask for one before a perm or big color change on previously processed hair too, since that hair reacts faster.
5. Follow every instruction on the pack, including the timing and any test it asks for first.
6. Handle colored hair gently. Wet hair is far more fragile than dry, so detangle slowly from the ends up and keep the heat low.
7. Condition after every shampoo, as the AAD advises. Conditioner binds readily to chemically damaged hair and lowers friction and breakage, but much of it washes out, so it helps only while you keep using it (Robbins 2012). For the lengths between washes, see what leave-in conditioner does.
8. Keep colored hair out of strong sun, which fades color, especially red and auburn shades; the AAD suggests a wide-brimmed hat.
9. If your self-check turned up several signs on lengths processed many times, the order of your next steps matters more than any single product. The table in how to repair damaged hair gives a first move for each kind of damage, and the free hair consultation puts yours in order.
10. Cut what you cannot manage; processed length leaves only as it is trimmed.

If a salon offers a bond builder with your color, we found no peer-reviewed evidence that such additives prevent coloring damage; read do bond builders actually work? before paying for one.

Can your hair still be healthy after dyeing it?

In the ways you can see and feel, yes, if each service is kept small. In the sense of being chemically unchanged, no. Colored lengths can be smooth and easy to manage, and dyed hair can even look shinier, because the color absorbs light scattered inside the fiber (Robbins 2012).

A workable definition of healthy colored hair: ends that feel close to the roots, detangle without snapping, separate when wet, and hold color about as long as they did when fresh. Care helps the first two, feel and detangling, mainly by lowering friction; color life depends more on washing and light. Care cannot bring back the surface lipid or the oxidized keratin in hair already processed.

ANATOMY's own Complete Reconstruction System pairs a shampoo and conditioner with the 100 ml Leave-In. It is made in Switzerland and patented, built on click chemistry, the reaction class recognized by the 2022 Nobel Prize in Chemistry, and independently tested at SGS proderm in Germany, on bleached hair. We make no claim for it on dyed, permed or relaxed hair that has not been bleached, or for keeping color from fading.

If your hair has been colored, permed or relaxed, start with the free consultation: find your Damage Profile.

Frequently asked questions

Does hair dye cause hair loss?

Dye damage, as this article covers it, shows on the hair shaft: hair breaking along its length. Hair coming out at the root, more shedding than usual, or any change in your scalp is outside what this article covers, and a dermatologist is the right person to ask.

Is box dye worse than salon color?

We found no study comparing them directly. What is documented is that where the color goes matters: touch-ups are meant for new growth only, and overlapping onto colored lengths adds damage (Gavazzoni Dias 2015). A kit pulled through the whole head each time processes the ends again; a root-only touch-up does not, wherever it is done.

Is dyeing hair darker less damaging than going lighter?

Usually. The AAD advises staying within three shades of your natural color and notes that going darker is typically better for hair, because lightening further needs more peroxide. Dark permanent shades still use alkali and peroxide, so they are not free of damage.

Is henna gentler on hair than permanent dye?

Its chemistry is gentler. Plant henna colors with lawsone at an acidic pH, with no peroxide or alkali (Robbins 2012). The one electron-microscope study of henna-dyed hair we found would not open, so we have no measurement of its effect on strength or the cuticle. Some metallic "progressive" dyes can react with later bleach, perms and other dyes.

Is a gloss or toner damaging?

It depends on the formula. A gloss or toner mixed with developer is another oxidative treatment on the same lengths, and it counts when you date your ends. Direct dyes, the kind used in semi-permanent color, develop without peroxide and involve no oxidation (Robbins 2012), so a gloss made only with direct dyes adds no oxidative step.

Why does my hair color fade so fast?

Mostly washing and light. Dye leaches out over repeated wash cycles, damaged and lightened hair loses it faster, and red and auburn shades fade most, with visible light doing much of the work (Zhang G 2016; Robbins 2012). We found no peer-reviewed evidence that sulfate-free shampoos, cold rinses or waiting days before the first wash slow fading.

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