Ever since dyeing my hair for the first time earlier this year, I've wondered exactly how a little bottle of liquid could turn my formerly chestnut brown hair into a sun-kissed blond. I know how to use it and what it does, but I couldn't name the individual components or explain how they interact to accomplish the end goal. So, I decided it was time to do some digging.
Originally, hair color was made from natural dyes like henna, red ochre, indigo, and even turmeric. It wasn't until the founder of L'Oréal produced the very first synthetic hair dye all the way back in 1907 that things began to change. Nowadays, modern hair dye is expertly formulated and much more precise, with most brands using a combination of natural and synthetic dyes to achieve subtle differences in shade and tone. But what are these individual ingredients, and what do they do? Keep reading to learn the science behind hair dye!
Ingredient #1: Ammonia
The first ingredient in hair dye, and maybe the most important, is ammonia. It's responsible for opening the hair cuticle so the color molecules can reach the cortex and deposit pigment. Without it, the pigments and developers couldn't pass into the interior of the hair strand.
Imagine the hair cuticle as you would shingles on a roof: If it lays smooth, it seals around the hair strand, keeping damaging or weakening chemicals out. Ammonia lifts and swells the cuticle, providing space for the pigment molecules to pass through. It also provides the right chemical environment for the dye to take hold. According to a report from Salon, "Because hair has an acidic pH by nature, ammonia also helps it become alkaline, to create a permanent change in color, particularly when creating high lift shades."
Here's the thing, though: Because of ammonia's rather, well, invasive effects on hair, if the right precautions aren't taken by yourself or the colorist, post-dye damage is an imminent possibility.
Ingredient #2: Alcohol
In today's market, most hair dye formulas contain some form of alcohol. So, be wary. Just like that glass of wine can dehydrate your body and skin, some forms of alcohol can also dry out your hair, leading to weak, damaged strands.
According to polymer scientist and cosmetic chemist Tonya McKay, the forms of alcohol to stay away from are short-chain alcohols. These are drying agents. Other long-chain alcohols, such as cetyl alcohol and stearyl alcohol aren't so bad. "Larger alcohols are typically derived from natural sources and have 12 or more carbons per molecule," she told Naturally Curly. "This higher amount of carbon content makes these molecules oilier (also referred to as 'fatty'). For this reason, they are often used as an emollient in skin and hair care products. They give a smooth, soft feeling to the hair shaft by helping the cuticle to lie flat on the surface of the hair."
Whether short or long-chain, alcohol increases absorption, meaning that your hair can take up more product, which leads to rich, seamless color. So if the formula does include alcohol, make sure it has super-hydrating ingredients as well, just to be safe. Take eSalon's formula, for instance. Every bottle of custom hair color that gets shipped out of its doors includes aloe vera, chamomile, wheat proteins, keratin, amino acids, and vitamin E. So dryness and damage are reduced.
Ingredient #3: Hydrogen Peroxide
Cue images of Roxie Hart in Chicago bleaching her hair with smuggled bottles of peroxide. In its purest form, and in large amounts, hydrogen peroxide is toxic to the human body. But fear not—the hydrogen peroxide used in hair dye is diluted multiple times to ensure safety if it comes into contact with your scalp.
Peroxide's primary duty is to lighten the hair. Once it's penetrated the cuticle, it bleaches out color, whether natural or previously dyed (this is also why hydrogen peroxide is an active ingredient in toothpaste—it bleaches old stains to reveal a whiter smile). It's critical to many hair dye formulas because it provides a fresh slate for new pigment to be deposited. This doesn't come without damage, though. Since it's stripping your hair, moisture loss and structural integrity is a big concern. You'll want to reach for a thick, nourishing hair mask to repair—try Shu Uemura Extreme Remedy ($68).
Ingredient #4: Pigments
Today, hair dye manufacturers use a blend of natural and synthetic pigments to achieve desired shades. Whether you're going darker or lighter, the molecules of the hair dye will react with the natural melanin that's already present in the hair.
Eumelanin and pheomelanin are both melanin molecules. Your hair color is a specific mix of these two pigments, as decided by your genes. According to Cambridge-based chemistry source Compound Interest, in dark-haired people, eumelanin is present in a greater concentration, whereas light-haired people have an excess of pheomelanin. Either way, the bonds of these molecules must break for a colorant to permanently change the color of your hair. Otherwise, the molecules would remain stable, as would your hair color. Ammonia, alcohol, and hydrogen peroxide work together to set off a chemical reaction, which involves breaking the bonds of pigments that are already present to deposit the new ones. This is the final step in the hair dye process.
Now that you have inside knowledge of how hair dye ingredients work, shop our favorite color damage prevention products below!