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The Biochemistry of Curly and Straight Hair


Willietta Gibson
Department of Biological and Chemical Sciences
Bennett College


This interrupted case study examines basic concepts of chemical bonding by telling the story of “Madison,” who is learning about the texture of her hair and how it can transition between its natural curly state to a smooth, straight texture. The case can be used to teach or review the major categories of bonds (ionic, covalent and hydrogen), major macromolecules of life, and hydrolytic and dehydration reactions. It also explores how chemical relaxers and heat through blow drying and flat-ironing can change the nature of straight, wavy and curly hair through the disruption of protein shape. Students learn what it means when a protein has become denatured and how various variables such as pH, heat and salts can lead to the unraveling of the three-dimensional shape of proteins. This case is suitable for an AP high school course, or for an introductory biology or chemistry course for majors or non-majors; it can also be used as a review of basic biology and chemistry for students in an upper-level biochemistry course.


  • Understand certain basic concepts of chemistry (e.g., covalent, hydrogen, and ionic bonds) that are relevant to introductory biology courses.
  • Describe the structure and function of major macromolecules and how they play a role in the formation and texture of hair.
  • Describe how the three-dimensional structure of proteins can be denatured or disrupted through heat and chemical treatments.
  • Create models that represent the chemical bonds and protein structures in hair.


Ionic bond; covalent bond; hydrogen bond; oxidation; reduction; ammonium thiogycolate; keratin; hair;

Topical Areas


Educational Level

High school, Undergraduate lower division



Type / Methods




Subject Headings

Biology (General)  |   Chemistry (General)  |   Science (General)  |  

Date Posted


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The following video(s) are recommended for use in association with this case study.

  • Protein Structure and Folding
    This animated video reviews the four levels of protein structure with engaging drawings and gentle humor. Running time: 7:45 min. Produced by Amoeba Sisters, 2018.
  • What Makes Hair Curly? Curly Hair Science Series Pt. 2
    This brief video uses a series of drawings to explain how disulfide bonds and follicle shape impact the texture of hair. Running time: 2:47 min. Produced by Kriya Botanicals, 2014.