Hair serves many purposes in our day to day life. It guards our scalp against the sun; it defends our nose and ears by trapping dust particles that contain harmful allergens and microbes; it even stops sweat and other particles from bothering our eyes. 

In terms of sensory function, hair is significantly more sensitive to air movement and surrounding environmental disturbances than skin. For example, when we’re cold or perceive potential danger, our hair stands up to trap a layer of air and add insulation; this is what gives the appearance of goosebumps. 

From protection and sensory input to temperature regulation and self-expression, hair plays a significant biological, social and emotional role in our lives. But how much do we know about its anatomy? 


Before we delve into the anatomy of hair, it is worth covering the two different types of hair: vellus hair and terminal hair. Vellus hairs are the short, fine, light hairs that cover the majority of the body, except for some parts such as the palms, soles, and lips. Their main purpose is to protect the skin and keep the body warm. The thickness, colour and length of vellus hair vary between individuals. 

Terminal hairs are the thicker, longer, and more pigmented hairs that are found on your scalp. When a baby is born, terminal hairs are solely located on their scalp, brows, and eyelashes, while the rest of the body is covered in vellus hairs. With the impact of androgens during puberty, some vellus hairs (for example, those on the beard, trunk, underarms, and genital region) develop into terminal hairs.

Humans have roughly five million hair follicles, with 100,000 of them being positioned on the scalp.


Hair is a filament that is mostly made from keratin and produced in the hair follicle. Keratin is the same protein that forms our skin and nails. Hair consists of two separate structures: the hair follicle below the skin and the hair shaft above the skin.


Hair starts growing within the hair follicle, a structure that begins in the epidermis (the skin’s top layer) and extends to the dermis (the second layer of skin). Hair follicles consist of a papilla, matrix, bulb and bulge.

  • The papilla is at the bottom of the hair follicle; it is a piece of tissue containing capillaries (small blood vessels) that nourish the hair root to keep it growing. 
  • The matrix, otherwise known as the germinal matrix, is also found in the lower region of the hair follicle. This is where cells produce new hairs when hairs die and fall out.
  • The bulb is a round, bulbous structure that surrounds the papilla and matrix. It is fed by blood vessels, meaning it’s the living part of the hair; any hair that is visible above the skin’s surface is actually dead. Within the bulb, there are many types of stem cells that divide every 23 to 72 hours, which is faster than any other cells in the body. It also contains hormones that affect hair growth and structure during different life stages; for example, during puberty and pregnancy.
  • The bulge is located in the middle of the hair follicle, which is also called the isthmus. It consists of stem cells that divide and regenerate hair follicles, sebaceous glands, and the epidermis. It also provides the insertion point for the arrector pili, which is a small band of muscle tissue. When these muscles contract, hairs stand on end, giving the appearance of goosebumps.



The hair shaft is the visible part of the hair. The shaft consists of three layers of keratin, which are:

  1. The cuticle, which is the outermost layer consisting of scale-like overlapping cells five to twelve deep. It is formed from dead cells, and gives the hair shaft strength and provides protection for the softer inner structures. The cuticle can be damaged by excessive use of heat (such as straightening irons) and by chemical damage (such as colouring, etc). Everyday elements such as the sun or wind, brushing, and harsh handling will also damage the cuticle.
  2. The cortex, which is the fibrous middle layer of hair consisting of keratin-filled, elongated cells that are cemented together with lipid-rich, flexible keratin. This gives the cortex the properties of elasticity and a high tensile strength. The cortex contains the pigment (melanin) that gives hair its colour.
  3. The medulla, which is the innermost layer of the hair structure consisting of sparse cells and air bubbles. Its role in humans is unknown, however in animals it helps to control body temperature.

The HAIR Growth cycle

While the structure of hair follicles is somewhat straightforward, their functions and growth cycle are complex. The rate of hair growth differs from person to person, however, hair typically grows 15 centimetres (or six inches) per year. 

Hair is always in one of the three stages of growth: anagen, catagen or telogen.


This is also known as the growth phase. Normal scalp hair follicles usually spend two to six years in the anagen phase. Anagen hairs vary in size; they can be long, thick terminal hairs or short, light vellus hairs. The hormones that come with puberty transform vellus hair into terminal hair. 

The anagen phase for eyelashes, eyebrows, and leg and arm hair is much shorter: between 30 and 45 days. This is why these hairs are much shorter than scalp hairs.


This is otherwise known as the regression phase and it spans two to three weeks; roughly 3% of all hairs are in this phase at any given time. During this stage, the rate of hair growth slows down, the hair follicles shrink, and they attach to the root of the hair. These hairs are now ‘club hairs’, which is the name for hair that has stopped growing.


This is also referred to as the resting phase and it lasts approximately three months. 10% to 15% of hairs are in this stage at any given time. After a few months, hair stops growing and becomes detached from the hair follicle. When the new hair starts to grow, it pushes the old hair out. We typically shed 50 to 100 scalp hairs a day, although many external factors can affect this, such as stress or medical conditions.


At 14 weeks of pregnancy, babies start developing hair follicles. By 22 weeks, they have all of their hair follicles, or at least openings in the skin where hair will grow. This equals roughly five million hair follicles, which is the largest number you will ever have. 

This is as hair follicles don’t continuously grow during life; as we age, the number of hair follicles per square inch actually decreases. This also means that the follicles that grow in the womb form the hair pattern that we have for the rest of our lives.

What determines the texture of our hair?

The texture of our hair – whether it’s straight, wavy, curly or a mix of all the above – is decided by the shape and structure of the cortex, and the medulla if it is present. Furthermore, the shape and structure of these two layers are determined by the shape of the hair follicle.

Hair growth starts with the production of keratinocytes by the basal cells of the hair bulb. When new cells are deposited at the bulb, the hair shaft is pushed through the follicle towards the skin’s surface. The process of keratinisation is complete when the cells are pushed to the skin surface to form the hair shaft (the part of the hair that is visible). The hair that you can see is entirely dead and made of keratin, which is why our hair does not have sensation. This also explains why you can shave, cut and colour your hair without damaging the structure of the hair.

What determines our hair colour?

Like skin, hair gets its colour from the pigment melanin, which is produced by melanocytes in the hair papilla. Differences in hair colour are genetically determined and can be attributed to different types of melanin. An abundance of the melanin called eumelanin gives black or brown hair; a very small amount of this results in blonde hair. A different type of melanin called pheomelanin gives red hair.

As we grow older, the production of melanin decreases, which is why hair loses its colour and becomes grey or white.


Hair was formerly divided into three main ethnic subgroups: Asian, African and European. However, due to recent studies, this classification has been broadened to include eight main subgroups based on three parameters: curve diameter, curl index, and the number of waves in the wave sequence.

During the categorisation procedure, it is necessary to take into account the structural characteristics of the hair follicle. Hair shaft diameters, hair follicle density, and the volume of the follicular infundibulum are just a few of the variables to consider.


Hair loss and thinning are natural processes that can have many reasons behind them. Attempting to understand these reasons is essential to treating or preventing them. If you are looking to learn more about your hair loss, the knowledgeable and highly trained team at Foli Sim are here to help. With three studio locations around Australia, they provide premium Scalp Micropigmentation services that begin with a free initial consultation. Visit their website today to book your appointment and start your journey to understanding your hair. Alternatively, complete our enquiry form and we can arrange your consultation.