Hair Dye: How Badly Does It Damage Your Hair?

woman gets new hair colour

Worried your hair dye is damaging your hair? This is what you need to know. |

If there’s a particular way you like to wear your hair, chances are good that you’re doing some damage to it in the process. Heat-styling tools can easily hurt your hair. Similarly, chemically straightening or curling your hair can leave it dried out. And using hair products that are bad for your health can damage your hair and exacerbate other health issues.

The problem is that it’s pretty easy to avoid thinking about how badly hair dye can damage your hair. That’s because we all have our routines. Whether you have a running appointment with your stylist or a long-standing love affair with your favorite drugstore hair dye, you know the drill. You’re used to the routine and probably don’t think too much about it, even if it involves damaging bleach or colors that simply won’t fade.

So if you routinely dye your hair, or are thinking about starting, now might be a good time to learn a little bit about exactly what hair dye does to your locks. Here’s what you must know.

Ammonia lifts the hair cuticle, and peroxide destroys the color

A Hari's salon employee has her hair rinsed

Here’s how hair dye stays in your hair. | Daniel Berehulak/Getty Images

Cosmetic chemist Ni’Kita Wilson explains to The Huffington Post that in order to deposit color onto your hair, the dye has to be able to get into the hair shaft. To do that, it has to move beyond the cuticle, which acts a little bit like tree bark and protects your hair from damage. To penetrate beyond the cuticle, hair dye uses ammonia to elevate the pH of the hair and to relax and lift the cuticle. Immediately, you’ve damaged your hair, since the cuticle isn’t meant to be lifted up.

Once the cuticle is lifted, the next step is to dye the hair your intended color. So, hair dye uses peroxide to break down your natural hair pigment. Peroxide is extremely drying to hair and is the reason why colored hair can take on a straw-like texture. As the peroxide developer sits, the cuticle remains lifted for the dye to penetrate into the open cuticle and hair shaft. The longer the cuticle is lifted, the more it weakens. Once you rinse your hair, the cuticle comes back down. But damage has already been done.

If you’re interested in the specifics of how the process works, chemistry teacher Andy Brunning reports on his blog Compound Interest that hydrogen peroxide is a strong oxidizing agent. It oxidizes the natural melanin pigments in hair, removing some of the conjugated double bonds that lead to their color, making them colorless. Actually dyeing the hair requires an alkaline pH, provided by the ammonia, which causes the cuticle to swell and can ultimately damage the hair.

Less-damaging alternatives don’t last as long

A hairdresser washing the hair of a client at a salon in Taipei.

You can try less-damaging hair dyeing methods, but they might not be as effective. | Mandy Cheng/AFP/Getty Images

If you use the wrong level of peroxide, or if you over-process your hair by constantly performing chemical treatments, you can continue to cause serious damage to your hair. Using semi-permanent or demi-permanent dyes, on the other hand, does less damage to your hair and can even add extra shine. (Semi-permanent hair dyes don’t contain peroxide, and demi-permanent dyes contain only low levels of peroxide.) But those colors are only going to last through a finite number of shampoos before fading and washing out. Because semi-permanent dyes don’t open the hair shaft, they won’t change your natural color.

So, while a temporary hair dye isn’t going to be as damaging as products that can permanently lighten and color your hair, many people find they need to dye their hair more often when using temporary options. That means that you’re exposing your hair (and your body) to the ingredients in your hair dye even more often than  you would with a permanent color.

Many companies have introduced ammonia-free hair dyes, using substitutes like ethanolamine. This is a milder ingredient and doesn’t cause the cuticle to swell as much as ammonia. But it washes out, unlike permanent colors that simply grow out, and isn’t as effective at lightening hair.

Damage can go beyond dried-out hair

A guest had their hair styled at the TRESemme Salon

Hair damage can be serious. | Donald Bowers/Getty Images

Almost everyone who’s dyed their hair knows they need to be extra gentle to freshly-dyed hair, and that they need to condition it thoroughly. Hair dye can definitely dry out your hair, but it can also cause your hair to become brittle and break if you overdo it on chemical processes. To keep your hair from becoming too dry and breaking off, you should condition regularly, and use a deep conditioning mask before and after coloring. You’ll also want to keep up this routine as needed to avoid breakage.

Also consider your cut. Everybody likes to have their preferred hair color and to maintain the length they like, but you may need to be a little bit flexible if your hair isn’t responding well to the formula you’re using. You need to get regular trims to prevent and remove split ends. It’s much better to keep your hair as healthy as possible, and go a little shorter than you’d like, than to walk around with hair that’s over-processed, too dry, and full of unhealthy (and unsightly) split ends.

The ingredients in hair dye can hurt your health, not just your hair

Lead hair stylist Stephanie Hayes uses Batiste Dry Shampoo backstage at the Charlotte Ronson Fall 2014 Presentation during Mercedes-Benz Fashion Week at The Hub at The Hudson Hotel on February 7, 2014 in New York City.

Hair dye ingredients can affect your whole body. | Cindy Ord/Getty Images

It’s not just your hair that hair dye can damage, either. The Environmental Working Group recommends minimizing your use of dark, permanent hair dyes. This is because many such hair products contain coal tar ingredients like aminophenol, diaminobenzene, and phenylenediamine, which have been linked to cancer. Coal tar is a byproduct of coal processing and is recognized by the National Toxicology Program and the International Agency for Research on Cancer as a human carcinogen.

It’s important to note researchers haven’t yet established a strong link between hair dyes and cancer, though some studies on people who color their hair regularly at work discovered a correlation with a minor increase in rates of bladder cancer. Because hairstylists and other professionals are exposed to the chemicals in hair dyes on a daily basis, European regulators have banned many of these ingredients in hair dyes. The FDA sanctions the use of coal tar in specialty products, including dandruff and psoriasis shampoos, but the long-term safety of these products hasn’t yet been verified.

Additionally, it’s worth noting allergic reactions to hair dyes are rare, but possible — and they’re a reaction you’ll want to avoid if you can. You should definitely patch test the first time you dye your hair or when you change colors, but if you can, it’s even better to test before every application.