Author: The Hair Doc

Properties of Hair-Part 1

Human hair approximately contains 65-95% protein, 15-35% water and 1-9% lipids. The properties of the hair, both physical and chemical, are directly related to these components.

What is Keratin?

keratinstructure

The keratin protein is a helicoidal group of cystine containing protein complexes. Like all proteins, keratin has three basic structures. It has a primary, secondary and tertiary structure. The primary structure is the amino acids that make up keratin and how they are bonded to each other. They are bonded through peptide bonds, disulphide bonds and hydroxide bonds. The secondary structure refers to the arrangement of the protein fibres to each other. Keratin from hair is an alpha protein forming twists which are coiled in an anti-clockwise direction. The tertiary structure refers to the ultimate shape the proteinaceous fibre takes. This is enabled by the presence of weak bonds such as hydrogen bonds.

What is the Primary Structure of Keratin?

Like all proteins, the primary structure of keratin is determined by the amino acid content. The amino acid content of hair is pretty much the same worldwide.

aminoacid

What is the Secondary Structure of Keratin?

The resulting keratin protein is shaped into an alpha-helix, which is held into place by special bonds.

 

i4_alpha_helix

What is the Tertiary Structure of Keratin? 

The hair proteins are then coiled together and then bundled into filaments which are further grouped together into larger bundles  of filaments.

coiledkeratin

In between the filaments within the matrix of the cortex lie Keratin Associated Proteins which confer added strength to these filaments. They are bonded to the filaments by disulphide bonds.

What are the bonds that keep the keratin structure together?

The final macromolecular structure of hair is due to the interaction of both intrachain (within chain) and interchain (between chains) bonds which hold the protein filaments together. The interactions are due to several chemical bonds including covalent (disulphide and peptide) bonds, salt linkages, hydrogen bonds, van der Waals forces and hydrogen bonds.

proteinsandbondsbondsinhair

 

References

Dekio S, Jidoi J. Hair Low-sulfur Protein Composition does not Differ Electrophoretically among Different Races. J Dermatol 1988; 15: 393-6.
Nappe C, Kermici M. Electrophoretic analysis of alkylated proteins of human hair from various ethnic groups. J Soc Cosmet Chem 1989; 40: 91-9.
Dekio S, Jidoi J. Amounts of Fibrous Proteins and Matrix Substances in Hairs of Different Races. J Dermatol 1990; 17: 62-4.
Baden HP. Biochemistry of hair protein. Clinics in Dermatology 1988; 6: 22-5.
Shimomura Y, Ito M. Human Hair Keratin-Associated Proteins. J Investig Dermatol Symp Proc 2005; 10: 230-3.

Draelos MD, Zoe Diana (2007-04-17). Hair Care (Kindle Locations 331-333). Informa Healthcare. Kindle Edition. 

Sources of Diagrams

intranet.tdmu.edu.ua

hairkeratins.com

teachers.yale.edu

Question of the Month – January

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Dear Doc,

I just had a baby boy and I got the same hair loss that I had after my first pregnancy. I expected that, but this time I noticed that my hair did not grow back the same way. It looks thinner in the front. What’s up with that? What can I do to stop this?

Concerned Mama

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Dear Concerned Mama,

Congrats on your second child!

Yes you have experienced the typical Postpartum hair shedding also known as Telogen Effluvium. During your pregnancy almost all of your hairs are in the anagen (growing) stage of hair growth. This is due to the high levels of the hormone oestrogen in the body which is known to keep the hair in the growing stage longer. As soon as your hormone levels go back to normal after delivering your baby boy, your hair follicles converted back to the regular 90% anagen :10% telogen. The telogen stage is the resting stage, the stage right before the hair falls out. What happens in some women is that this shedding can reveal latent or hidden Female Pattern Hair Loss (1) resulting in decreased density in their hair at the front of your scalp right behind their hairline. Some of their hairs have grown back in smaller, finer and thinner.  Their parts look much bigger than usual and they see more scalp. Look at your family members. Do all the men have hair? Do the women have thin hair as well? If so, this is unfortunately showing up in you as well.

So what can you do about this? If you’re not breastfeeding, you can try topical 2% or 5% Minoxidil (Rogaine is a brand) twice a day. It is available over the counter in a lot of countries. If after four to six months you do not see an improvement you may need to visit a doctor to see whether or not you may need oral medication to help slow down your hair loss.

 

(1) Birch, M. P., Lalla, S. C. and Messenger, A. G. (2002), Female pattern hair loss. Clinical and Experimental Dermatology, 27: 383–388. doi: 10.1046/j.1365-2230.2002.01085.x

Question of the Month

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I am using Rogaine for my hair loss, but I noticed that it makes my hair quite dry and keeps stripping my hair colour. What can I do?

 

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This is a common question that is asked  by many many women who have Female Pattern Hair Loss and are using topical 5% Minoxidil (whether Rogaine brand or otherwise). It’s a catch 22 situation. On the one hand, it is helping keep or grow their hair but, on the other, it is wreaking havoc on the hair itself.

The solution more than the foam is the usual culprit. It contains a high concentration of (denatured) alcohol in which the minoxidil is dissolved. Alcohol, is notorious for drying out skin and hair. It does  so, because it is a small volatile molecule. This aids in rapid drying of the product, but because alcohol can dissolve natural oils, it can take with it much needed oils when it evaporates from the scalp and hair. The alcohol can also dissolve the hair dye, thus making the colour disappear rather quickly, much to everyone’s annoyance.

So what can be done?

  • Use the Foam preparation. It doesn’t  have  denatured alcohol present in the ingredients. It is less likely to dry out the hair.
  • Use a Temporary Colour. These include hair rinses, mascaras, colour mousses, crayons or sprays. These will coat the hair shaft and will not penetrate. They will last up to 3 days or longer depending on how often you wash your hair. This will help to extend your hair colour.
  • Use Sulphate Free shampoos. These are the new “it” products in the cosmetic industry. They are less stripping than the regular shampoos. They will make your hair clean but not squeaky clean thus reducing the any contribution from the  shampoo stripping the hair of the hair dye.
  • Use Deep Treatments.  Rinse out conditioners do not deposit enough replacement oils, fatty acids, proteins etc to decrease the effects of the dye on the hair. Deep treatments tend to be thicker, and are filled with potent ingredients. For dry coloured hair, they should be left on the hair for 30 minutes to an hour on a weekly basis or used every other week.

 

The Hair Shaft

The hair shaft is made of a hard protein called keratin. This is the same keratin that comprises skin and nails. The hair shaft has three major components: Cuticle, Cortex and Medulla. It tends to remain uniform in size whilst in its growth phase. The width and shape of the hair shaft is determined by the hair follicle.

The Cuticle

The cuticle is the outermost layer and is composed of several layers of cells, (5-10), arranged in a pattern similar to shingles on a roof. The free edge of the cuticular cells, lie up and outward, with the free edge facing the direction of the tip of the hair shaft. The microstructure of the cuticle is shown below:

cuticleindetail

The Epicuticle

This is the outermost layer. It is a protein layer with an overlying lipid (fatty acid) layer.

The A Layer

This is proteinaceous layer found at the outer part of each cell. It is compromised of a high percentage of cystine, > 30%. It is rather hardy and is highly resistant to chemical and mechanical attack. Supports the attachment of free fatty acids to the hair’s surface.

The Exocuticle

Closely abuts the A layer, and forms approximately 55% of the cuticle. Also comprised of a high amount of cystine. It is not as rigid as the A layer.

The Endocuticle

Comprised of cellular debris that is pushed to one side during the formation of the A Layer and the Exocuticule. It is softer than the other two layers, and easily swells with water. This therefore affects how the hair shaft responds in water.

The Cellular Membrane Complex

This is composed of lipids, primarily fatty acids: 18 methyl eicosanoic acid (18-MEA), palmitic and oleic acids. This layer determines the combing properties of hair in the wet and dry state. Older and damaged hair have decreased percentage of fatty acids.

The Epicuticle

This is thought to determine the surface properties of the hair.

 

The Cortex

The cortex forms the bulk of the hair shaft. The cells are long and elongated. They are fused tightly to each other. Each cell contains fine filaments called microfibrils. These microfibrils are  made of highly helical proteins giving the unique characteristic of alpha – keratin. The microfibrils are then grouped together  in larger bundles called macrofibrils. These bundles are packaged in a certain manner forming the  paracortex, orthocortex and mesocortex. The packaging of these fibrils help to determine the hair type.

hairshaftcortexarrangement

The Medulla

This structure is not always present. It is usually found in hair fibres of a larger width. The function of the medulla is unknown in humans. It contains a mixture of glycogen, melanosomes and air bubbles. The medulla tends to have a pattern: continuous or discontinuous.