Hair biology that every cosmetic chemist needs to know

Most people working as formulators in the cosmetic industry have a solid background in chemistry. It’s not a requirement that you have a degree in chemistry and there are many formulators with degrees in biology, physics, biochemistry, or chemical engineering. I even knew a formulator with a degree in anthropology. But a chemistry degree is what most people have. 

This means that most formulators didn’t get any more than the minimum requirement of study in biology. In reality, most people who studied biology didn’t really go into depth on the most important topics of biology for formulators including hair, skin, and nails. This is unfortunate because knowing the basic biology of these systems can help you create better cosmetic formulas.

However, you don’t have to know every detail about hair and skin biology to be a good formulator. But there are some basic facts that every formulator should know. In this post we’ll focus on hair. In a future post we’ll focus on skin.

1. Hair is dead - You can’t make hair more healthy because it is just a dead fiber. There are no nerves, no blood supply and no living cells in a hair fiber. Once hair leaves the inside of your skin, it’s dead tissue. It’s no more alive than a shoe lace.

2. Hair is composed of mostly keratin - Hair is protein and made up of mostly amino acids. The structure of hair is what makes it have different properties than skin, nails and horns which are also made up of keratin.

3. Hair color is the result of melanin - There are cells in the follicle that create melanin pigments which are injected into the growing hair fiber. These melanin pigments are responsible for all the natural hair colors observed. Pheomelanin produces red and blonde hair colors while eumelanin produces brown and black colors.

4. Gray hair is the absence of color - While the various melanin molecules create the hair color, gray hair is what results when no melanin is injected into the fiber. Gray hair is really just uncolored hair.

5. The shape of a hair fiber depends on the shape its follicle. Hair gets pushed out of the head through a tiny hole. The more circular the hole, the straighter the fiber. The more elliptical the hole, the more curly the hair.

6. Hair has 3 main structures - Cuticle, Cortex, and Medulla. The cuticle is the out layer of the hair and takes the shape of shingles on a roof. It is responsible for hair shine, smoothness, and ease of combing. Hair products mainly interact with this layer. The cortex is the inner structure of the hair which is responsible for the fiber strength and flexibility. The medulla is the inner core of the hair fiber which is often just empty space. It’s not known what it does.

7. There are 3 stages of hair growth - Anagen, Catagen & Telogen. The growth phase is the Anagen phase in which hair strands get longer. It can last anywhere from two to six years. The Catagen phase is a transition time when the hair fiber stops growing and detaches from the growth portion of the follicle. It lasts about two weeks. The Telogen phase is a dormant phase of the hair follicle and lasts anywhere from 1 to 4 months. At the end of this phase the hair follicle starts growing again and the Anagen phase commences. Hair grows about 0.5 inches per month.

8. Hair fiber diameter changes as people age.  It starts out thin and gets thicker as a person enters adulthood. Then it begins to get thinner and become more fine with advancing age. Maximum hair length changes too with older adults having generally shorter growing hair.

9. S-S bonds between hair protein fibers (from cysteine proteins) give hair strength. These bonds are what get broken when curly hair is relaxed and straightened.

10. The isoelectric point of hair is near pH 3.67 - Hair doesn’t technically have a pH because it is not an aqueous solution however, the surface of hair has a net negative charge when exposed to pH solutions higher than this number. That’s why cationic ingredients (positively charged) are more substantive to hair than anionic materials.

There is much more you can learn about hair biology but knowing these basic 10 facts will help you in future formulating efforts.

Perhaps the best book about the biology of hair for cosmetic formulators is the Chemical and Physical Behavior of Human Hair.  It’s an excellent reference for all things about hair biology.