Chemistry of Colors and Curls

Hair has no fun in sun . . . or at beauty salon

Bad hair days have chemical roots. The dyes and perms at a salon, the humidity of

Scanning electron microscopy image of a ripped-open hair shows the fibrils that make up its interior. Pande

A transmission electron micrograph of a partial hair cross-section shows the hair’s outer cuticle as lines. Melanin (black spots) gives the hair its natural brown color. Pande

Sunlight fades dyed hair: When researchers covered the top and bottom sections of a tress and then simulated sunlight, the middle section of the hair faded. Wis-Surel and Irum Chaudhury

Micrograph of uncombed, unconditioned hair. Ramaprasad

Micrograph shows how combing wet hair breaks off the hair cuticle. Ramaprasad

When combed, hair first treated with conditioner suffers less damage. Ramaprasad

Acidic solutions of pH2 and 4 (pH is indicated in black) changed the hue of dyed hair more than less-acidic solutions did. Wis-Surel and Irum Chaudhury

lazy summer days, even the routine shampooing, styling, and combing of your hair

can foster chemical alterations that do a number on your do.

A cadre of researchers–call them hair scientists–hears your hair screaming. In

their lab experiments, these scientists investigate how the natural environment,

including sunlight and humidity, changes hair’s structure and color. They also

identify the microscopic details of unintended damage from styling, dying, and

other attempts to beautify hair.

Such work has led the scientists to create new technologies for studying hair

damage on the molecular level. But hair research is not only about finding

damage–it’s also about preventing damage. For example, researchers have found how

certain treatments, such as conditioning, help maintain hair’s strength and how

others minimize color change in dyed locks.

Hair damage

One of the largest sources of hair damage is the quest for beauty. “Nobody is

happy with what they have,” says Chandra Pande, a biophysicist with Clairol in

Stamford, Conn. Brunettes often want light hair. Blondes want to go brown or red.

Meanwhile, those with mops of curly hair think their locks are too frizzy, and

those with straight manes want curls.

“That’s what keeps us busy,” Pande says.

Protein makes up about 95 percent of a human hair. The rest is fatty molecules,

such as lipids, and pigment molecules. Pande notes that when procedures such as

bleaching or perming change the chemistry of hair, they alter the protein-rich

internal structure of the fiber. “You can imagine how much damage it does,” he


In their laboratory, Pande and his colleagues go far beyond imagining such things.

Their aim is to determine how different treatments lead to changes in hair. Hair

chemists need sensitive methods for recognizing and measuring various types of

damage in their effort to identify milder hair products and more-effective

treatments, Pande says.

Speaking last May in Towson, Md., at the 34th Middle Atlantic Regional Meeting of

the American Chemical Society (MARM 2001), Pande discussed some of the methods

that his lab uses to identify hair damage. Since typical human hairs are only 60

to 80 micrometers in diameter, it takes tools as powerful as the scanning electron

microscope (SEM) to get a close-up look.

Currently, he is examining the chemical creation of curls in the lab, which

depends on disulfide, or sulfur-sulfur, bonds found within hair’s protein

molecules. During a perm, such bonds are initially broken with a chemical

treatment that erases the “memory of the hair,” he says. Once hair is held in the

desired shape, new bonds are formed with a second chemical step.

Pande speculates to Science News that some of the lasers he uses to study hair

protein might someday be adapted for use in salons. He envisions a day when a

stylist might adjust the treatment to maximize the number of disulfide bonds that

break during the first stage of the perm and that form during the resetting stage.

He notes that permed hair typically has only 90 percent of the original number of

disulfide bonds, leaving the hairdo weaker than before.

On another front, Pande is also developing analytic techniques to understand

sunlight-induced damage. This photodamage makes hair brittle and can alter its

color. Molecules of the amino acid tryptophan in the hair, which naturally

fluoresce when illuminated, decompose when exposed to the sun’s ultraviolet light.

Pande has found that a decrease in tryptophan fluorescence from a person’s hair

can quantify damage from UV radiation.

Rinsing out conditioner

To protect hair from such damage, researchers also use powerful technology to test

potential products. Much of the work of identifying the perfect conditioner or

hair sunscreen is done in the secrecy of company labs. However, some of these

tests are conducted for consumer products companies by outside researchers, such

as the hair scientists at the nonprofit research institute TRI/Princeton in New


In one such test, for example, TRI researchers examine how much conditioner

remains on hair following rinsing, says K.R. (Ram) Ramaprasad of TRI. As any

number of television commercials point out, excessive conditioner buildup can

weigh hair down. To see how conditioner coats a hair, Ramaprasad and his

colleagues use SEM and a technique called microspectrofluorometry in which the

chemists attach fluorescent molecules to the conditioner.

By fluorescently tagging chemicals such as potential additives for shampoos and

conditioners, Ramprasad and his colleagues can also tell companies how the

compounds penetrate a hair on the microscopic level. Mapping the course that the

chemicals take as they penetrate hair fibers helps identify the compounds that

cause the least damage.

The TRI group also tries to find out how to get the best results from a promising

product. In one case, the researchers have recently been developing computer

models to better determine how much of a liquid is needed for an optimal coating.

Such models might one day suggest the amount of hairspray needed for the best

hold, for example.

Hair-care researchers look for ways to protect tresses against day-to-day damage

as well. SEM studies by TRI scientists demonstrate how even the simple act of

combing can harm locks. Almost anything a person does to hair damages it, says


Each hair’s surface is covered by cuticle–a layer of protective, shinglelike

flaps. The abrasion of combing dry hair essentially sands down the cuticle layer,

says Ramaprasad.

The situation worsens under wet conditions. Absorbed water makes hair fibers swell

and the cuticles stick out. In this case, combing can actually break off the

protective flaps. Conditioners minimize this breakage by getting under the cuticle

and holding the shingles down, notes Ramaprasad.

Heat styling can be hard on hair, too, even when it makes the strands feel

smoother to the touch, says Kathleen Martin, a hair researcher for Unilever in

Rolling Meadows, Ill.

More than half of women in the United States blow-dry their hair at least six

times a week, and some 70 percent use a curling iron or hot rollers more than once

a week, says Martin, who also spoke at MARM 2001.

Blow-drying at typical temperatures of 40 to 70C removes the hair’s weakly

bonded water. Unlike permanents, which break and make disulfide bonds, the loss of

water alters the weak hydrogen bonds in the hair’s nexus of protein molecules.

That’s why, for example, blow-drying can change curly hair to straight.

But hair styled this way often doesn’t stay straight for long. When the air has a

high relative humidity, blow-dried hair absorbs moisture from the air, and the

hairdo loses its blow-dried style, says Martin.

Blow-drying doesn’t damage hair dramatically, but curling irons can. They heat

hair to much higher temperatures than blow-dryers do, remove strongly bonded

water, and destabilize proteins, weakening the hair shaft, notes Martin. These

molecular changes enable hair to hold a new look for longer than blow-drying does.

Even weeks later, ironed hair still has less water than it did before the

treatment, says Martin.

“It’s a tenacious water loss,” Martin says. “You’ve really changed the hair in

some substantial way.”

Flat irons get even hotter than curling irons do. Flat ironing can make hair feel

smoother because the cuticle lies flat. Indeed, flaps look melted in SEM images.

The damage also goes deep into the hair’s interior, says Martin.

Sunlight and hair

Sunlight introduces more subtle molecular damage to hair. Scientists have known

that ultraviolet and visible light break chemical bonds, but Ramaprasad wondered

whether such actions depend on the hair’s environment. Would hair exposed to

sunlight in Arizona, New Jersey, and India break down into the same chemical


In fact, the chemistry is different, Ramaprasad reported in New Orleans last May

at the Annual Scientific Seminar of the Society of Cosmetic Chemists. His

spectroscopic studies have demonstrated that exposure to sunlight produces

different chemical reactions depending on the degree of humidity and the intensity

of sunlight. For example, sunlight is harsher on hair in humid environments than

in dry ones.

The effect of the environment on dye in hair is also a hot topic for hair

chemists. Humidity, sunlight, and other factors can affect dyed hair dramatically,

says Gabriela M. Wis-Surel, a hair scientist with Unilever in Edgewater, N.J. At

MARM 2001, she described several recently completed studies in which she used UV

and visible spectroscopy to study dye absorption.

Wis-Surel examined hair colored by oxidation-dye chemistry–a technique for

obtaining color that’s not supposed to wash out. Two processes occur

simultaneously in such dyeing. A developing agent, generally hydrogen peroxide,

oxidizes the pigment melanin to lighten the hair’s natural color. Meanwhile, the

dye penetrates the hair fibers.

Although these dyes are marketed to people with a “long-term commitment to color,”

Wis-Surel says, she discovered that the color is not nearly as committed as its

wearer–at least not right away. Some dyes continue to react with the hair over the

first 2 or 3 days, she found. The color of a person’s hair when he or she leaves

the salon might not be exactly the same a few days later. The transition to the

final shade is subtle, Wis-Surel says, but her work confirms reports by some

attentive consumers.

Over the long term, Wis-Surel found that several factors alter a permanent dye’s

color. To observe sunlight-damaged hair, she simulated an intense month of Miami

daylight by shining a xenon lamp for 48 hours on each side of a flattened tress of

hair. The light greatly increased color loss, she says.

Similarly, high humidity lightened color and added a yellow tinge to dyed hair,

she says. A single humid day at the beach won’t produce noticeable changes, but a

week could, she points out. Wis-Surel also found that such color changes “seemed

to be reversible.” Placing hair samples back in low humidity returned them to

their previous hue.

Other factors alter the color of hair samples, too, reports Wis-Surel. A simulated

month of shampooing–1 hour in an agitated beaker–faded the color of dyed hair,

although not as badly as sunlight and humidity did. Tips lost more color than

roots, she notes.

Meanwhile, Wis-Surel found that an acidic environment of pH 4, as in some shampoos

and conditioners, produced more color changes, especially in red shades, than a

less acidic treatment with pH 6 did.

Yet of all the factors studied, sunlight was the most damaging to dye color, Wis-Surel says.

Simple steps

This may be more chemistry than most people are willing to contemplate while

lounging on the beach. But Pande says there are simple steps that people can take

to protect their hair.

To avoid sun damage, for example, he recommends wearing a hat and using hair-care

products that contain sunscreen.

Or just don’t worry about it. If your hair does get damaged, be patient. It

eventually grows out. “Go to the barber,” Pande recommends.

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