Scientific Concepts and Principles of Barbering
What to know cold
The barbering sciences section tests how the hair, skin, and the tools that touch them actually behave. You need the structure of the hair (cuticle, cortex, medulla), the growth cycle (anagen, catagen, telogen), and the fact that hair is mostly keratinized protein. Know the pH scale (0-14, 7 neutral; hair and skin sit around 4.5-5.5; alkaline products swell the cuticle, acidic products close it). Understand the difference between physical and chemical changes in hair, and how water, heat, and chemicals each affect the hydrogen, salt, and disulfide bonds.
Traps to expect
Questions love to test bond types: hydrogen bonds break with water and heat (temporary), salt bonds with pH shifts, disulfide bonds only with chemical relaxers or perms (permanent). Another trap is confusing the layers of the hair shaft with the follicle. Also watch for wording about the direction of pH change and what it does to the cuticle.
Rule of thumb
Remember "water and heat bend, chemicals rebuild." If a stem describes wet styling or thermal tools, the answer is a physical/temporary change. If it names a relaxer, perm, or color, think disulfide and permanent.
Worked example
A client's hair was straightened with a thermal iron last week and is curly again after washing. What bond was affected? Because water and heat reversed it, the answer is hydrogen bonds, a temporary change, not a chemical service.