A girl and three boys with green, pink, and blue hair

L-R: SANNYSLENE SOUSA/EYEEM/GETTY IMAGES; MARYANN ATAR/EYEEM/GETTY IMAGES; JONATHAN KIRN/GETTY IMAGES; SUE BARR/IMAGE SOURCE/GETTY IMAGES

STANDARDS

NGSS: Core Idea: LS2.A, ESS2.A

CCSS: Reading Informational Text: 2

TEKS: 6.5A, 7.6A, 8.3B, C.3B, C.4A

Hair Color Chemistry

Brush up on the science of hair dye

September 20, 2021

By Jess Romeo

AS YOU READ, THINK ABOUT the chemical reactions needed to change the color of a person’s hair.

Have you ever spotted someone with neon green hair or watched a celebrity show off their new pastel purple ’do? Maybe you’ve even colored your own locks. No one is born with technicolor tresses—shifting shades requires hair dye.

Hair gets its natural color from a pigment called melanin, which comes in three main forms: brown, black, or red. The amount and type of melanin in a strand of hair determines its specific hue.

Have you ever seen someone with neon green hair? Or a celebrity showing off their new pastel purple ’do? Maybe you’ve even colored your own locks. No one is born with technicolor tresses. To change shades, you need hair dye.

Hair gets its natural color from a pigment called melanin. It comes in three main forms: brown, black, or red. A strand of hair has a certain amount and type of melanin. That determines its color.

For thousands of years, people used a variety of substances, like plants and minerals, to alter their hair’s color. Today, synthetic, or artificial, hair dyes can color natural hair, as well as weaves and extensions, to just about every shade imaginable.

Some dyes are temporary—they provide only a brief color change. These dyes contain large pigment molecules that coat the surface of the hair strand and wash off with a single shampoo.

For thousands of years, people changed their hair’s color. They used different substances to do this, like plants and minerals. Today, we have synthetic, or artificial, hair dyes. They can color natural hair or weaves and extensions just about any shade.

Some dyes are temporary. They change hair color only briefly. These dyes contain large pigment molecules that coat the surface of the hair strand. They wash off with one shampoo.

For slightly longer-lasting color, there’s semi-permanent dye. It contains smaller pigment molecules, explains Trina Espinoza, a science communicator who hosts the YouTube show “Ms. Beautyphile.”

These molecules can penetrate the hair’s cuticle, or protective outer layer, so the color takes longer to fade.

Semi-permanent dye is for slightly longer-lasting color. It contains smaller pigment molecules, explains Trina Espinoza. She’s a science communicator who hosts the YouTube show “Ms. Beautyphile.” These molecules can enter the hair’s cuticle, or protective outer layer. That’s why the color takes longer to fade.

“If you really want to commit to a color, you might be ready for the third type of dye—permanent dye,” says Espinoza. It contains ammonia (NH3), which causes the hair’s cuticle to swell and open. A stylist mixes the dye with hydrogen peroxide (H2O2), a chemical that breaks down melanin and lightens the hair. This allows dye-forming molecules to enter the hair’s cortex, or secondary layer. The new color will remain until the hair grows out.

For the best results, it’s important for people to understand the chemistry of whichever dye they choose, says Valerie George, a hair color expert for salon brand John Paul Mitchell Systems. From bold color to subtler shades, George believes that “dyeing your hair is all about having fun and expressing yourself.”

“If you really want to commit to a color, you might be ready for the third type of dye—permanent dye,” says Espinoza. It contains ammonia (NH₃). This chemical causes the hair’s cuticle to swell and open. A stylist mixes the dye with another chemical, hydrogen peroxide (H₂O₂). It breaks down melanin and lightens the hair. Then dye-forming molecules can enter the hair’s cortex, or secondary layer. The new color will remain until the hair grows out.

When people choose a dye, they should understand its chemistry. That leads to the best results, says Valerie George. She’s a hair color expert for salon brand John Paul Mitchell Systems. You might choose bold or quieter shades. But George believes that “dyeing your hair is all about having fun and expressing yourself.”

CONSTRUCTING EXPLANATIONS: Select two types of hair dye described in the article. What are the key similarities and differences in how they work?

WHAT IS HAIR?

The average human scalp contains about 100,000 hairs. Each strand grows out of a tiny pouch below the skin’s surface called a follicle.

SEBACEOUS GLAND

This organ secretes an oily substance to prevent hair and skin from drying out.

NERVES

Nerves in the scalp sense hair movement.

SHAFT

This part of the hair sticks out from the surface of the skin.

ROOT

This part of the hair lies under the skin.

BLOOD VESSELS

Blood carries nutrients to cells at the bottom of the follicle.

MEDULLA

Not all hair contains this innermost core. It is usually found in thick or coarse strands.

CUTICLE

Hair’s outer layer is made of a tough protein called keratin arranged in overlapping scales.

CORTEX

The hair’s middle layer contains melanin pigments, which create red, black, and brown hair color. Hair with a low level of pigment appears blond.