What Hair Dye Actually Does To Your Hair, According To Science

A lot of people dye their hair, but that doesn't necessarily mean they know what they're actually doing to their locks. Specifically, they might not know what dye does to your hair follicles, from a scientific point of view. The majority of us just schedule our monthly hair appointment, sip our coffee in the chair as we fill our hairdressers in about our latest dating escapades, and wait until the foils are set and blow driers are switched on. Or, if we're feeling strapped for money that month, we might just head over to our corner drugstore and choose the best bottle of dye we can find.

There's usually not a lot of questioning involved here. We just get used to certain routines and beauty rituals. But, IMO, there should be a lot of questions involved when changing the state of your hair. For example, what's that harsh smell coming out of the bottle? Or how does a dark, rich color magically turn light and summery? What strips away the color, and how does a new one stick around, even after dozens of washes? When you think about it, it all sounds borderline magic.

But it's actually some cold, hard science. Below are facts of what hair dye actually does to your hair.

1. The Ammonia In Your Hair Dye Breaks Through Your Hair Cuticles

Hair dye doesn't just rinse across your hair and stain it. It actually has to break through a couple of barriers to set permanently. In order to get into the hair shaft, it has to get through the hair's natural protection: the cuticle.

And how does it get past that obstacle? The ammonia in hair dye lifts the cuticle up to let the molecules of the dye in. As cosmetic chemist Ni'Kita Wilson told Huffington Post, "This chemical elevates the pH of the hair, and in doing so, the cuticle relaxes and lifts up." That way, we can move on to step two.

2. And The Peroxide Strips Away Your Current Color

Now that the cuticle is broken, you can actually dye your hair the color you want. In order to do that, you have to use peroxide (aka bleach) to remove your natural color and make room for the new pigment.

Wilson told Huffington Post, "That's where the peroxide comes in, and that breaks down your natural hair pigment. Peroxide is very drying on the hair, which contributes to the damage of the hair. Now the cuticle is lifted, your pigment has been broken down, so now your hair should be straw-like."

But what does "removing" your natural hair color actually mean? According to Natalie L. Nichols, health and beauty writer at wellness site SparkPeople, "Bleach oxidizes the color proteins in the hair, leaving them colorless." Basically, it bleaches out the color and makes room for the new molecules.

3. Then The New Color Pigment Gets Deposited

Now that the cuticle is lifted, the original hair color proteins become oxidized and colorless, and the new color pigment can take over and bond to the hair cortex. According to Randy Schueller, cosmetic scientist and writer at cosmetic science blog Beauty Brains, the hair dye is a series of chemicals that "start out as tiny molecules (called monomers) that are small enough to penetrate into your hair shafts. Then when they are there, they react with each other to create bigger molecules (called polymers). These polymers are so big that they can not be washed out of your hair." And that's how the dye sticks to your mane!

4. Ammonia-Free Dyes Still Lift Your Cuticles

So, ammonia is needed to lift the cuticle of your hair and to start the whole process of dyeing. But what if you go with an ammonia-free dye because you heard it was less damaging? The thing to keep in mind here is that the cuticle is still lifted with a substitute agent called ethanolamine, just not lifted as much.

According to Andy Brunning, chemistry teacher and writer behind science education blog Compound Interest, "This is a milder agent, but also doesn’t cause the cuticle to swell as much as ammonia, meaning it has a few aesthetic drawbacks: It often washes out after a certain time period, unlike permanent colorings which merely grow out, and isn’t as effective at lightening hair."

In the end, it might be gentler on your cuticles, but you might find yourself re-dyeing more frequently as your hair color washes out faster.

5. The Longer You Dye, The More Damage You Cause

While the dye is sitting on your head, the molecules are going into the strands and developing. But the longer the cuticle is lifted (so, the longer the dye is on your head,) the more damage is done to your hair. Ni'Kita Wilson told Huff Post, "Keep in mind that your cuticle is lifted for however long you have before you rinse, and the dye is penetrating into your open cuticle and hair shaft. The longer your cuticle is lifted up, the more it's weakening. Once you rinse, your cuticle comes down because the color has deposited, but the damage is already done."

The conditioners put on your head afterward are actually what close the cuticles back up and lock in the new color, so the longer they're lifted, the more your hair weakens.

6. That Harsh Smell Isn't So Scary

So what exactly makes that eye-watering smell that we're all too familiar with when we walk into a salon? It smells harsh and chemically, and quite possibly like it could burn through steel, let alone our tresses.

Don't worry, it's actually not that scary.

Nichols went on: "When the peroxide reacts with the proteins inside the hair it releases sulfur — and that coupled with the ammonia is STINKY!" That smell is science, people.

7. Your Hair Won't Actually Fall Out

There's always that worry that if you over-dye your hair, you'll kickstart some sort of hair loss episode. But there's actually no evidence that hair dyeing causes as much.

Nichols told SparkPeople, "A bad color job can cause hair to dry out and create breakage that can be confused with hair loss [...] Thoroughly conditioning your hair before and after coloring goes a long way to prevent your hair from becoming brittle and breaking. Another factor that can lead to confusion on this topic is that over a lifetime there is a certain amount of hair loss that occurs naturally. Many times this natural hair loss coincides with graying hair and more frequent trips to your stylist." So there you have it: As long as you condition it properly to prevent your hair from becoming brittle, enjoying a monthly dye job shouldn't make you go bald.

Now that you're armed with the facts, your next visit to the hair salon or drugstore box dye aisle should be a little more enlightening. You now know exactly what you're doing to your hair, and can rest easy over the harsh smells, scary words (bleach! peroxide!), and threats of David Letterman hairline futures. Science doesn't lie.

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