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The Chemistry of Hair Highlights

Difficulty
Time Required Average (6-10 days)
Prerequisites None
Material Availability Readily available
Cost Average ($50 - $100)
Safety Adult supervision required for working with hydrogen peroxide-based hair lighteners. Wear protective gloves and eyewear. Read and follow the safety notes in the Experimental Procedure section, below.

Abstract

Have you ever tried to make parts of your hair lighter than the rest of your hair? Perhaps the way you tried to do it did not lighten it or maybe it turned out a weird orange color? With this science project you can understand why.

Objective

The goal of this project is to investigate how hydrogen-peroxide based hair treatments change the color of human hair.

Credits

By Cecilia Cuba

Edited by Andrew Olson, Ph.D., Science Buddies

Sources

  • Milady Publishing Company, 2000. Milady's Standard Textbook of Cosmetology Albany, NY: Milady Publishing Company, a division of Delmar Publishers, Inc.
  • Nizetich, A., 1993. Milady's Teaching Hair Coloring: A Step-by-Step Guide to Building Props Albany, NY: Milady Publishing Company, a division of Delmar Publishers, Inc.
  • Heavilin, S., ed., 2002. Milady's Illustrated Cosmetology Dictionary Albany, NY: Milady/Thomson Learning.
  • The figures in the Introduction on human hair structure are from:
    Tobin, D.J., 2006. "Biochemistry of Human Skin—Our Brain on the Outside," Chem. Soc. Rev. 35: 52–67, available online at [accessed January 10, 2007] http://www.rsc.org/delivery/_ArticleLinking/DisplayHTMLArticleforfree.cfm?
    JournalCode=CS&Year=2006&ManuscriptID=b505793k&Iss=1
    .

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Last edit date: 2013-01-10

Introduction

Bleaching, lightening, or de-coloring (removing pigment) hair can be achieved by using natural sunlight or chemicals designed specifically for this purpose. Using sunlight alone, the results achieved will depend on the natural color of the hair. Visible results can take several weeks or months. If the natural hair color is darker than a medium blonde, the most successful way to lighten the hair is using hydrogen peroxide and an ammonia-based hair lightener.

hair with chemically lightened highlights

In order to understand how the process of chemically lightening hair works, it is important to understand the structure of a shaft of human hair. Figure 1, below (from a scientific article on the biochemistry of human skin by Desmond Tobin, Ph.D.), illustrates the microscopic structure of a human hair. The left-hand panel of the illustration (Figure 1a), is a cartoon of a human hair shaft with a cut-away view to show the inner structure. Each strand of hair has an outer layer of flattened cuticle cells (Cu), which surround the fibrous cortical cells (Co). The medulla (Md) is a central core of cells in the hair shaft. Also shown is a microfibril (MF) within a cortical cell. The middle panel (Figure 1b), shows an actual hair shaft under the microscope. You can see how the flattened cuticle cells (Cu) have a scale-like appearance when magnified. The dark central medulla (Md) is also visible. The right-hand panel (Figure 1c), shows a cross-section of a fine human hair. Here you can see that the cuticle cells (Cu) are highly flattened, and wrap around the cortical cells (Co) in many layers. The cortical cells contain the dark pigment granules that give each hair strand its natural color (Tobin, 2006).

microscopic structure of human hair shaft
Figure 1. Microscopic structure of a human hair shaft. Part (a) shows a cutaway cartoon of a single hair shaft. The labels show cuticle cells (Cu), cortical cells (Co), the medulla (Md), and a microfibril (MF) within a cortical cell. Part (b) shows a transmitted light micrograph of a single hair strand. The scale-like layer of cuticle cells (Cu) is clearly visible, as is the central medulla (Md). Part (c) shows a cross-section of a fine hair strand. The flattened cuticle cells (Cu) wrap tightly around the cortical cells (Co), which contain many dark pigment granules (Tobin, 2006).

The predominant proteins in hair are from the family of keratins, the same family of proteins that make your fingernails. Protein molecules are built from amino acids. In a hair strand, the keratin molecules contain a large number of a particular amino acid called cysteine. Each cysteine in the keratin molecule is a potential attachment point, where the keratin molecule can be tightly connected to another cysteine, forming a chemical bond called a cross-link. The keratins in hair have many such cross-links, making a hair strand strong and flexible. If you are interested in finding out about how hair grows, you should do research on hair follicles, the specialized structure in the skin that produces each individual hair strand.

The cuticle cells also have a coating of specialized molecules that repel water. These molecules are called lipids. By repelling water, the lipid molecules help to protect the hair strand. In order for bleaching chemicals to reach the pigment molecules in the cortical cells, the cuticle layer (including its protective lipid coating) must first be opened up. In chemical lightening solutions, this opening is accomplished by making the solution basic. You should do background research on the pH scale, to learn about basic, neutral, and acidic solutions. See the Bibliography for resources to get started.

The hair pigment goes through different stages of changing color as it lightens. The amount of change depends on how much pigment the hair has and the length of time the hair is exposed to the lightening chemicals. Lightening can be divided into roughly seven stages from the darkest to the lightest. A natural head of black hair will go from black to brown, to red, to red-gold, to gold, to yellow, and finally to pale yellow (almost white). The hair also becomes more porous (increasing the hair's capacity to absorb liquids) during the lightening treatment.

Hydrogen peroxide (H2O2) is an oxidizing chemical that bleaches the natural pigments in human hair. For hair treatment, the concentration of hydrogen peroxide is often expressed in volumes, referring to the total volume of oxygen (at standard temperature and pressure) that can be produced from the hydrogen peroxide. A "10 volume" solution is equivalent to 3% hydrogen peroxide in water (weight/volume, i.e., 3 grams of H2O2 plus enough water to make a total volume of 100 ml). A "20 volume" solution is equivalent to 6% hydrogen peroxide, etc. (Wikipedia contributors, 2006). The higher the concentration of peroxide used the greater the breakdown of melanin (tiny grains of pigment which create natural hair color) resulting in a lighter color.

Hair lighteners are available for use in liquid, cream, and powder form. By mixing a chosen concentration of hydrogen peroxide and a lightener, then applying the mixture to natural hair, we can achieve visible lightening of selected pieces of human hair. In this experiment, you will compare the results of lightening hair with a commercial product to untreated hair, and to hair treated with a "natural" hair lightener such as lemon juice or sunlight.

Terms and Concepts

To do this project, you should do research that enables you to understand the following terms and concepts:

  • human hair strand, structure, composition, how it grows:
    • cuticle,
    • cortex,
    • pigments: eumelanin, phaeomelanin.
    • keratin,
    • hair follicle.
  • understanding the pH scale is helpful for this project,
  • hydrogen peroxide (H2O2).

Questions

  • How are "volumes" of hydrogen peroxide related to concentration of hydrogen peroxide expressed in percentage terms (weight/volume)?
  • How does the pH of the bleaching solution affect its ability to lighten hair?
  • How does sunlight lighten hair color?

Bibliography

  • Most libraries should have copies of these books. (Note that each has multiple editions with different publication dates; the particular edition is not critical.)
    • Milady Publishing Company, 2000. Milady's Standard Textbook of Cosmetology Albany, NY: Milady Publishing Company, a division of Delmar Publishers, Inc.
    • Heavilin, S., ed., 2002. Milady's Illustrated Cosmetology Dictionary Albany, NY: Milady/Thomson Learning.
  • These sites explain the pH scale:
  • For a start on background information on hair lightening chemicals, try these references:
  • The figures in the Introduction on human hair structure are from this (advanced!) article, which contains excellent illustrations of hair follicles and hair shafts:
    Tobin, D.J., 2006. "Biochemistry of Human Skin—Our Brain on the Outside," Chem. Soc. Rev. 35: 52–67, available online at [accessed January 10, 2007] http://www.rsc.org/delivery/_ArticleLinking/DisplayHTMLArticleforfree.cfm?
    JournalCode=CS&Year=2006&ManuscriptID=b505793k&Iss=1
    .

Materials and Equipment

To do this experiment you will need the following materials and equipment:

  • swatches of chemically untreated human hair:
    • approximately 1.5 cm wide × 10 cm long;
    • light brown or darker color;
    • 'chemically untreated' means no permanent waves, no hair color (or even beat up from styling with blow dryers and curling irons);
    • you should be able to obtain these from a beauty salon.
  • at least 6 ounces hydrogen peroxide-based developer, in both "10 volume" (contains 3% hydrogen peroxide) and "20 volume" (contains 6% hydrogen peroxide) concentrations; notes:
    • These are the most commonly available volumes at beauty supply stores open to the public.
    • You will need a parent or guardian to purchase.
    • You could also ask at a beauty salon if the salon would be willing to help you with obtaining some.
    • If you can get "40 volume" developer (contains 12% hydrogen peroxide) this would expand the experiment.
    • Most hydrogen peroxide in hair lightening kits sold at superstores or drug stores would be "20 volume."
  • hair lightener, powder or cream type; notes:
    • Available at beauty supply stores open to the public.
    • You will need a parent or guardian to purchase.
    • You could also purchase a hair lightener (highlighting) kit from a superstore or drugstore.
    • You could also ask a beauty salon if they would help you in obtaining these.
    • You will need at least enough for one application on a typical head (i.e., the amount from one kit).
  • tint brush; notes:
    • Available at a beauty supply store open to the public, or
    • use a stiff brush approximately 4 cm wide.
  • plastic or glass bowl (no metal),
  • protective gloves (latex or vinyl),
  • protective eyewear (e.g., goggles),
  • aluminum foil,
  • lemon juice or other natural lightener for comparison,
  • sturdy tape or small elastic bands (for mounting swatches on board).

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Experimental Procedure

Safety Note: Use caution with the hydrogen peroxide solutions in this project.

  • Wear protective gloves and eyewear.
  • The solutions can bleach your clothing if they splatter, so it's a good idea to wear a lab coat or old clothes.
  • Avoid contact with skin and eyes. If contact occurs, immediately flush with lukewarm water.
  • Obtain medical assistance for eye contact.

  1. Do your background research so that you are knowledgeable about the terms, concepts and questions, above. It is especially important that you research and understand the terms and structure of the human hair strand.
  2. For chemically lightening a swatch of hair, use the following procedure:
    1. Secure one end of each hair swatch with an elastic band or sturdy tape.
    2. Wear protective gloves when mixing and using the hair lightener solution.
    3. Mix the hair lightener in a bowl.
      • If you are using powder lightener, use approximately 2 tablespoons of powder. Add enough hydrogen peroxide to make a creamy paste about the consistency of honey.
      • If you are using a cream lightener, mix enough hydrogen peroxide to make a honey consistency.
      • For a fair comparison (for example, if you use different concentrations of hydrogen peroxide) use the same amount of hydrogen peroxide for each solution you make.
    4. Lay a hair swatch on a piece of aluminum foil.
    5. Apply the lightening mixture to the hair swatch with the stiff brush. Saturate the swatch with the mixture.
    6. Leave the mixture on the swatch for a set amount of time, for example, 10 minutes.
    7. Rinse the hair swatch with tap water.
    8. Dry the hair swatch.
    9. Remember to label each swatch and keep track of the treatment for each swatch (e.g., hydrogen peroxide concentration, lightener used, length of treatment time) in your lab notebook.
  3. Keep one hair swatch completely untreated for comparison.
  4. For comparison to peroxide treatment, try sunlight or another "natural" lightening treatment.
  5. For sunlight bleaching you can try this method:
    1. Put a swatch of hair in a secure outdoor location that receives direct sun (preferably afternoon).
    2. Do this for at least 1 week.
    3. Compare to untreated and chemically treated swatches and note your results.
  6. For "natural" chemical lightening, you can try this method:
    1. Put enough lemon juice (or other natural lightener, such as chamomile tea) on the hair to saturate the hair swatch.
    2. Place in the sun (will not work without sunlight) for several hours.
    3. Rinse hair with tap water.
    4. Dry hair.
    5. Compare to untreated and chemically treated swatches and note your results.
  7. Note that you can use the hair swatches on your display board to show the actual results of your experiment.

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Variations

  • Try different concentrations of hydrogen peroxide. What are the results in lightening the hair using "10 volumes," "20 volumes," and "40 volumes" peroxide?
  • Are the results different if the lightener is left on the hair a longer time?
  • What happens if the natural lightener or the mixture dries out on the hair? Does drying out stop the process of lightening?
  • Compare effects on different types of hair. What is the degree of lightening on hair that is very dark (i.e., dark brown or black)? What is the degree of lightening on hair that is light to begin with (i.e., medium to light blonde)?
  • Does adding heat (heat lamp) make a difference in the time or lightening of the hair?
  • What condition is the hair left in after the lightening? Dry, rough, dull, or possibly destroyed? Does the length of time that the hair is exposed to the lightener solution affect the condition of the hair? Does a different concentration of peroxide affect the condition of the hair? Design an experiment to find out.
  • Since chemical treatments must open the cuticle layer for the bleaching molecules to reach the pigment in the cortical layer, do chemical treatments permanently alter the structure of hair? One possible method for investigating this question is to build hygrometers using humain hair. A hygrometer is a device used by weather forecasters to measure the relative humidity of the air. Human hair strands expand when the humidity is higher, and contract when the air is dryer. See the Science Buddies project Does Chemical Lightening Affect the Structure of Human Hair?. You will compare hygrometers made with untreated hair strands to hygrometers made with hair subjected to chemical lightening treatments. Can you see any differences between the treated and untreated hair?

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