How Hair Grows

The Ins and Outs of Hair Growth

Hair growth in humans is far from being a straightforward and simple process, although on the outside it might seem as such. Quite interestingly, like many other processes in the body, all our hair follicles are developed while still a foetus, with no more being produced throughout our lives. In fact, hair growth starts as early as the 22nd week in the journey of human development. At this period of the foetus’ life, the hair follicle has no pigment and is white. Although early in the development phase, the foetus already has in the vicinity of five million hair follicles over the entire body, while the scalp has approximately one hundred thousand and the entire head has about one million.

Hair Structure and Features

Although keratin is often associated with our fingernails, toenails and skin, hair is also made up of this exceptional protein. The structure of the hair strand is layered in a concentric format, forming the cuticle, cortex and medulla. The medulla layer provides protection to the delicate hair shaft, while the cuticle provides protection to the cortex and is on the external part of the hair shaft.

The structure of the hair itself is also complex. The hair shaft is the part of the hair that can be seen on the scalp and consists mostly of the cortex. The hair follicle, however, is contained within the skin itself and sits right down in the dermis. In order to afford protection to the hair follicle, a mechanism is required. This is where the inner sheath and outer sheath come into the equation. An oil gland, known as the sebaceous gland, produces sebum. The inner sheath is located next to this gland in order to condition and protect both the hair and the surrounding skin (less is produced as we age). The outer sheath, however, sits right into the gland and is located close to the erector pili muscle. It is this muscle that acts to secrete oil from the gland. Capillaries within papilla sit at the base of the follicle and deliver nutrients to the cells, while the part of the hair follicle that is living, the bulb, sits around the papilla. This bulb divides at a more rapid rate than any cell (i.e. each 24-72 hours).

Although the cuticle has no colour, it is the cortex that determines your hair colour as it the component that contains the melanin. For people with dark hair, the cortex contains eumelanin, while if you have red hair, the cortex will contain a substance known as pheomelanin. Those who have less melanin in the cortex have light coloured hair (e.g. blonde). The colour of our hair also determines how many hair strands we have. For example, a blonde will have approximately 140,000 hair strands. This is compared to a brunette who has 105,000 and a redhead who has 90,000. The cortex also determines the type of hair a person has in terms of straight or curly. Round cortex produce straight hair, while oval cortex produce hair that is wavy / curly.

Hair Growth: Stages and Characteristics

Although there are a number of factors that affect how much a person’s hair grows each day and year, it is typical for it to grow between 0.3-0.4 millimetres per day, equating to about six inches in one year. Not only is hair growth determined by a person’s age, their lifestyle, how healthy they are and their genetics; the rate of hair growth also differs on different parts of the head. For example, the area known as the crown on the scalp experiences the fastest hair growth

Three phases are said to make up the hair growth cycle: Anagen, Catagen and Telogen. An individual’s hair will experience these three phases in slightly different ways depending upon the actual type of hair they possess. That is, whether a person has either vellus or terminal hair will dictate how they experience hair loss. For example, vellus hair is fine, colourless and is fuzzy in appearance (a.k.a. peach fuzz). Terminal hair, however, is darker and can been seen easily when looking at it. Upon a person experiencing hair loss or balding, albeit from medicines, age or any other follicle damage, the fine, colourless and hard to see vellus hair replaces the dark, visible terminal hair.

The three phases of the hair growth cycle include:

Phase 1: The Anagen Phase. Known as the “active” phase of the hair growth cycle, in the Anagen stage, on average, hair growth is at the rate of one centimetre each 28 days. This phase also occurs in the hair found throughout the body as well, including on the arms, legs and eyelashes. A stage that lasts somewhere between two and six years, the cells at the base of the hair rapidly divide and the club hair is pushed up the hair follicle and out of the scalp. Evidence of a short Anagen phase can be seen in those people whose hair never seems to grow past a certain length.

Phase 2: The Catagen Phase. This stage is significantly shorter than the Anagen phase and only takes place between two and three weeks. Once this stage commences, it indicates that the Anagen phase has finished. A “transitional” period, only approximately three percent of a person’s hair is present during this phase. It is at this stage when the club hair is produced. That is, each follicle reduces to a fraction of its original size (approximately one sixth). This decrease in size means that it needs less nutrition from the blood in order to survive. It is here that the actual follicle and the hair root attach.

Phase 3: The Telogen Phase. Only in the Telogen stage for approximately 100 days, this phase is known as the “resting” period. That is, the hair follicle rests while the club hair is produced in its entirety. During the Telogen phase, only approximately six to eight percent of all hairs are present. It is the resting stage, in particular, where individuals seem to notice hair shedding (also called the Exogen period). In fact, it is standard to lose about 25-100 hairs every day during this phase.

Reasons for Hair Loss

There are a myriad of reasons people suffer from hair loss. Some of these hair loss reasons can include nutritional deficiencies; stress; genetic factors; hormonal imbalances; and, certain medical conditions and medicines associated with their treatment.

  • Mineral and Nutritional Deficiencies

Despite eating well and consuming what many consider a healthy diet, mineral imbalances can occur. For example, cooking food, instead of eating them raw or steaming them, can lead to deficiencies. On top of this, mineral supplements do not always replace what the body needs to maintain a healthy scalp and hair growth. In fact, some mineral supplements can actually cause mineral imbalances in the body, upsetting your body’s natural state. For these very reasons, it is important that prior to consuming mineral supplements, a person must be aware of any imbalances that currently exist. This is where a mineral and metal analysis can assist, identifying the levels and the ratios that are present in the body.

Another example of mineral imbalances in the body that affects hair growth is that of toxicity. In our modern diets, there are significant sources of toxic metals (e.g. drinks and foods, cleaning products and our working environments). The mineral and metal analysis can pinpoint levels of these very substances in the body, such as lead, aluminium, arsenic, tin and even mercury.

  • Stress and Anxiety

A common by-product of our modern day lives, scientific studies have proven an association between what causes hair loss and stress. In many instances, the impact that stress has upon our bodies and hair is also made even worse by certain dietary inclusions, such as alcohol, caffeine and artificial sweeteners. In such cases, the medical profession suggests that Vitamin B complex be taken to counteract the impacts of these nasties. It has been shown that this vitamin has the ability to make the body’s nervous system stronger and stop the white blood cells from attacking hair follicles – a core reason hair growth can cease and hair can be shed. As such, vitamins and a relaxing exercise can help reduce stress hair loss.

  • Genetics

Genetics can play a large part in hair loss, particularly the condition known as Androgenetic Alopecia. With 70% of the male population and 40% of the female population suffering from this condition, people go bald because of both genes and androgens. Although genetics can affect hair loss in a myriad of ways, when the gene is X-linked (e.g. in the androgen receptor) it means that the baldness gene comes from their mother and the hair loss pattern will be similar to that seen in their grandfather on their mother’s side. This is why in this type of male baldness, men do not resemble their father’s baldness pattern as much.

Generally, however, this is not the only genetic cause of hair loss or male baldness. That is, if a male’s father suffers from baldness, they are two and half times more likely to also suffer from hair loss – suggesting more than just the X-linked gene is responsible.

In some cases, genetics cause hair loss which is not sex-linked. These are called autosomes and are gained from each parent arbitrarily. Genetic hair loss is still in its early stages in terms of scientific understanding. At this point in time, it is the X-linked gene, the androgen receptor, that is still the main indicator of how and whether a male is going to experience hair loss and balding.

  • Hormonal Imbalances

Hormonal imbalances are also a major culprit of hair loss in both males and females. These can often take the form of progesterone, testosterone, oestrogen, cortisol, dihydrotestosterone and aldosterone. When hormones become high or unbalanced in the body, many people experience hair loss. That is, for men it can be in the form of DHT shrinking the hair follicles or for women perhaps pregnancy or shortly following the cessation of birth control. In particular, as people age, hormonal imbalances begin to affect the body and hair growth. That is, in men, testosterone decreases by ten percent every decade after the age of thirty. In women, pre- menopausal, menopausal and post-menopausal females also experience a drop in certain hormones. Because hair loss occurs specifically in these years due to decreasing hormones, many individuals source medication to balance their hormones and thus treat their hair loss or balding. There are also many myths surrounding testosterone and men. For example, it is a common wives tale that men with large amounts of testosterone in their bodies experience hair loss younger – none of which is true.

  • Health Conditions and Medical Treatment

It is quite common for people to experience hair loss after they take medicines. Of all the types of hair loss caused by individuals, it is taking medications or Telogen effluvium hair loss, which is the most common. In this type, individuals experience hair loss about two to four months following consumption of the medication and the hair follicle enters the resting phase much sooner than it would otherwise. This is when the person begins shedding. Another type of hair loss due to medicines is that of Anagen effluvium, whereby hair loss occurs in the active growing stage instead of growth occurring. Normal division by special cells is blocked due to the mediation. One of the most common examples of Anagen effluvium is seen in chemotherapy patients. Depending upon the dose and type of drug they are prescribed, it is not uncommon for chemo patients to experience the loss of hair in clumps or complete balding all over the body, including the scalp. In the case of chemo drugs, which are often extremely powerful, hair loss is quite normal and can be severe. Adriamycin, cyclophosphamide, cactinomycin and docetaxel are typically the chemo drugs that produce the most significant hair loss.

The number of medications that are responsible for hair loss is simply astounding. From antidepressants to birth control, weight loss to high blood pressure medicines, hormone replacement to thyroid, epilepsy to steroids, there are a whole range of medications that are used to treat quite common conditions that can cause hair loss.

  • Age

Hair loss can also just simply occur with age. That is, the volume of hair a person has often reduces as we get older – despite our genetic makeup and hormonal balance / imbalance. Although hair loss and growth tends to occur in a cyclical pattern, the fact of the matter is there is no escaping decreased volume as we get older. It is the actual follicle that changes with age – that is, in both length and width. From the perspective of the onlooker, this hair looks like it is thinned out. Ultimately, the number of these finer hairs simply decreases and the hair breaks rapidly. On a positive note, in these patients, the area where the hair is to be sourced from on the scalp retains enough hair to be used in hair transplanting – a common procedure for those individuals who are even in their seventies.