Why do you need to understand the basic science of hair?
Most cosmetics are applied to either the skin or hair, so by understanding the basic science of either will enable you to become a better cosmetic chemist. You’ll have a better understanding of how to formulate hair care products (e.g. shampoos, conditioners, eyelash products, facial hair products, etc.).
What is hair?
Hair is a filamentous biomaterial that consists mainly of proteins (keratin) and amino acids. Hair keratin is formed by amino acid molecules that are linked by a cysteine-disulfide bond — these bonds in hair are what make the structure of hair unique in comparison to skin keratin, but this can be for a different lesson.
Hair has multiple functions depending on its location, and the location of hair might be a little questionable to some people… but I’ll carry on. Simply, hair are dead fibers that protect you (e.g. eyelashes protect your eyes from dust) and keep you warm (think about those caveman commercials you’ve seen in the past).
Layers of Hair & How it Grows:
The Hair Shaft consists of the cuticle, cortex, & medulla.
- Cuticle: outer layer that protects the hair, is responsible for the “shine” that we see & ease of combing
- Cortex: layer that mainly consists of keratin protein & structural lipids, is responsible for the structure and flexibility of the hair
- Medulla: center layer of hair
The shape of hair depends on the Hair Follicle. The more circular, the straighter the fiber. The more elliptical, the more curly it will be.
1. Your hair begins growing from a root in the bottom of the follicle. The root is made up of cells of protein.
2. Blood from the blood vessels in your scalp feeds the root, which creates more cells and makes the hair grow.
3. The hair gets pushed up through the skin as it grows, passing an oil gland along the way. The oil gland adds oil to the hair and keeps it shiny and soft. It can make it greasy, too. That’s why you need to wash your hair.
4. The hair dies by the time it is long enough to poke out through the skin. Yes, hair is dead. That’s why it doesn’t hurt to get a haircut.American Academy of Dermatology
Hair in Relation to pH & Cosmetic:
Things that we learned in Biochemistry (yes!):
- Isoionic point: the pH at which a protein has an equivalent number of positive and negative charges
- Isoelectric point: the pH at which a protein does not migrate in an electric field — the net charge of hair is neutral at this point
- Its isoionic point is around pH 5.6 — I’ll give it a range of 5.0-6.0 since everyone’s hair can differ.
- The isoelectric point of hair is around pH 3.67 — I’ll give this a range of 3.5-4.5.
Essentially, anything applied to hair with a pH above the isoelectric point of hair will create negative charges, resulting in fly aways & frizz! That’s why when you go outside and moisture hits your hair, your hair begins to frizz — it’s becoming more negatively charged.
If the isoelectric point of our hair is ~3.67, wouldn’t it make sense for our hair-care products to be formulated in that range to minimize fly aways & tangled/dull looking hair?
It actually may be a difficult thing to achieve if you begin to consider situations such as eye-irritation, especially in infants — the concept of tear-free shampoo will typically be shampoos with a higher pH than the suggested isoelectric point of hair. Therefore, I would suggest not using children’s shampoo for adult-hair.
Furthermore, if you do formulate hair care products or use hair care products with pH above ~3.67, I would suggest using cationic agents to reduce electrostatic forces between hair fibers for reduced frizz & fly aways. Conditioners will typically carry these cationic agents.
Like skin, I would suggest that the pH of our scalp is around 4.0-6.0. If you wish to formulate a scalp-specific product, I would suggest formulating the product in this pH range to minimize skin irritation.
Also, if you wish to formulate an eyelash product, I would suggest that the product either be anhydrous or have a pH even above a 5.0 due to irritation and sensitivity. You can always utilize cationic agents or conditioning agents to off-set the “pH of hair”.
As a cosmetic chemist, not only do you have to think about the science of hair when you are formulating, you also have to think about the intended use of the product & how you can minimize possible irritation while maintaining efficacy.
Look forward to the next sections of COSCI 101 – The Basics: Cosmetic Padacts
Continue learning about the basics of cosmetic chemistry with Cosmetic Padacts in the next sections of COSCI 101. Get information on hair chemistry and more in-depth information on topics in cosmetic chemistry. Follow us on Instagram (@cosmeticpadacts) & Facebook for updates on upcoming posts.