Hair Dye: How Badly Does It Damage Your Hair? By: Jess Bolluyt

woman gets new hair colour

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