The Hair: Structure and Function

Ok, I admit that the first time I wrote this I was lazy and not at all interested in the layers of the hair shaft, so I didn't really do the topic justice. I'm re-publishing this now with improved information!


Within your dermis, there's a very cool structure called the hair follicle which projects through your dermis and epidermis and creates your hair. The average human has 100,000 follicles on their head!

The follicle has many different components, all of which have their own function.
Dermal Papilla- This area is full of connective tissue and has a blood supply, but cell division does not take place here.
Matrix- Around the papilla there is the matrix, a collection of epithelial cells and melanocytes (pigmented cells). Cell division to form the hair shaft and follicle occurs here.
Root Sheath- There is a sheath that covers the root of the hair shaft, and there are multiple layers within this sheath, the inner layers are continuous with the hair shaft.
Bulge- I'm not sure that anyone truly knows exactly what this does, but there are some who believe it communicates with the Matrix, helping to control hair growth.
Sebaceous Gland- This tiny gland produces sebum (oil) which is excreted on to the skin.
Arrector Pili Muscle- It's not seen in this pic, but there is a little muscle that will contract when you're cold or afraid, which makes the hair stand up!


What is hair made of?
-80% protein, primarily keratin
-10-15% water
-5-10% pigments, minerals and lipids

The hair itself has a lot of different layers, most of which don't really matter to us in the long run, truthfully. There really are 3 main layers to the hair shaft once outside of the skin. All three of these layers emerge from the matrix, where the cells are dividing rapidly. As the cells are pushed up (and out) they dehydrate and die, forming the layers of the hair as the remaining pieces of the cells keratinize, becoming harder. The layers of the shaft are:
• Inside (medulla)
• Middle (cortex)
• Outside (cuticle): The outer layer consists primarily of keratin and really does look like shingles on a roof like you see in all of those conditioner commercials! This layer really determines how shiny your hair is. If the shingles are laying down well, your hair is shiny due to light reflection. The cuticle also holds the inner layers together, so if it is damaged (eg- a split end) the hair shaft is dramatically weaker.


I found a website that listed the "Optimal" daily nutrition for great hair. Here's what they recommended, recommended daily intake, and what's in Centrum:

Vitamin	Foods	"Hair Recommendation"	RDI	Centrum
Vitamin C	Oranges or Boiled Broccoli	75 mg	60 mg	90 mg
Biotin	Eggs, Yeast, Peanuts, Cauliflower	100 mcg	3 mg	30 mcg (10% RDI)
Iron	Red Meats, Cereals	15 mg	18 mg	18 mg
Zinc	Red Meats, Poultry, Chickpeas	15 mg	15 mg	11 mg
Folic Acid	Yeast, Liver, Lentils, Asparagus, Oranges, Lemons	300 mcg	400 mcg	500 mcg

You can see that it's pretty easy to maintain good hair growth with a good diet, and if necessary with supplementation with pretty much any over the counter supplement.

Hair Follicle Image
Layers of Hair Image