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Did You Know Your Hair Follicle Is Considered an Organ?

We’re obviously hair obsessed, but the little we know about what’s actually going on with our manes (read, what it’s made of, and how or why it grows) is kinda cray. To find out the true biology of hair, we reached out to Dr. Dominic Burg, Chief Scientist for évolis Professional and he gave us an entire course worth of information. Break out the caffeine and prepare for Hair Bio 101.

Why Hair Grows

“The hair on your head is actually a dead fiber,” explains Dr. Burg. What makes it grow is the action of small organs known as hair follicles, and these follicles control hair growth over repeating hair cycles. “Hair follicles are actually true organs, much like any other organ in your body and like other organs, are made up of different parts that do different jobs,” he says.

The key areas of a hair follicle are outlined below:

 (Image courtesy of Dr. Burg)

The body requires a lot of energy to get hair in a good place. “Ultimately, hair follicles are little machines geared up to manufacture hair shafts out of keratins. The follicles have to work extremely hard to do this 24/7, burning a lot of energy in the process. The body’s control over the process is complex and like anything complex, it can be quite easy to disrupt the balance and for things to go a little awry. This is part of aging, but it is also the root cause of hair loss and thinning,” says Dr. Burg.

“Individual hair follicles can be thought of as cycling, dynamic, independent mini organs,” he explains further. That is, all hair follicles on the human head independently go through a cycle of growth, rest, shedding and regrowth that occurs many times throughout life. While in many animals (like cats and dogs) the hair cycle is seasonal and relatively synchronized resulting in molting, the hair cycle in humans is not synchronized and hair follicles on your head will all be at different points in the hair cycle. “This means that humans will shed about 100-120 scalp hairs a day, every day of the year,” says Dr. Burg – and I suddenly feel more chill about my post-shower hair cluster.

Hair Growth Cycle

hair follicle organ

 (Image courtesy of Dr. Burg)

Dr. Burg explains that the hair cycle is a repeating pattern of growth, rest and fall that happens many times over your life, with the average hair cycle being 6 or 7 years in length. The hair on the head is not cycling in unison, rather the hair cycles asynchronously, with each hair following its own timing and pattern.   This leads to the loss of about 100 hairs a day, which is completely normal — if this sounds like a lot, you have to remember that you have around 100 000 to 150 000 hairs on your head, so this only represents 0.1% of your total hair, and after they fall they are generally replaced by a new hair growing in its place. “Each new hair is regenerated from a reservoir of different types of stem cells; epithelial and mesenchymal, that live near the bulge region and dermal papilla, respectively,” he emphasizes.

If you really want to know about how your hair functions, you have to familiarize yourself with the growth phases, summarized by Dr. Burg.

Anagen: The anagen phase is the growth phase of the hair where the hair fiber is growing and elongating. In a normal adult, about 80% of the follicles on the head will be in anagen at any given time. The anagen phase for scalp hair follicles usually lasts for between 5 and 7 years.

Catagen: In the catagen phase, the hair stops growing and goes through a process known as regression that lasts about 10 days. During regression, the dermal papilla detaches and the follicle shrinks. About 1% of the hair follicles on the head will be undergoing catagen.

Telogen: Telogen is the resting phase of the hair cycle where the follicles are relatively dormant for approximately 2 to 4 months. Approximately 9% of the hair follicles are in Telogen at any given time. During telogen the stem cells from the bulge come into proximity to the remnant dermal papilla cells and when a critical concentration of growth signaling molecules is reached, the new hair follicle (also called a hair germ) migrates downwards and a new hair begins to form.

Exogen: As a new hair is forming in the telogen phase, the old hair is gradually released and pushed out. This shedding of the old hair shaft to make way for a new one is known as exogen, or sometimes called kenogen.

Signaling in the Hair Cycle

“The different stages in the hair cycle are mediated by signaling molecules and growth factors,” he continues. “The concentrations of these molecules in and around the cells in the hair follicle changes during the hair cycle, and this invokes the specific hair cycle events in the different parts of the follicles.” In general, there are two main types of signaling molecules: positive regulators which tell the cells to grow divide and produce the hair shaft and negative regulators that tell the cells to stop growing and rest, illustrated here.

hair health biology

 (Image courtesy of Dr. Burg)

If the hair cycle is the center of hair growth, it is also at the forefront in hair loss.   The hair cycle has quite a complicated physiology and biochemistry, and like anything complicated, it is very easy to upset the balance and get out of control. Things like changes in diet, stress, hormones, and the aging process can upset the hair cycle. “What we see in almost all forms of hair loss and hair aging is shortening of the growth phase of the hair cycle. When the growth period becomes too short, hair falls out too quickly, excess shedding occurs, and the regenerating hair comes in finer and is less substantial. Unfortunately for some, follicles can become so dysfunctional that they no longer produce hair at all. Once you have reached this stage the only option is hair transplantation,” he notes.

“At evolis our breakthrough technology revolves around one of the key players in the hair cycle hair cycle dysfunction and hair loss: a special molecule called fibroblast growth factor 5, or FGF5 for short,” he says. FGF5 is what is known as a negative regulator of hair growth and is often referred to the “master regulator” of the hair cycle. The only job of FGF5 is to tell hair to stop growing and start resting. So too much FGF5 means that there is more hair fall, less hair growth, slower hair growth, and the growth of finer, less substantial hair. “We also know of a FGF5 is hair specific, meaning it doesn’t have any other jobs in the body. Its only job is to signal hair to slow down, stop growing and start resting. The fact that FGF5 is hair specific means that it can be targeted without unwanted effects in other parts of the body.   In fact, humans that naturally don’t have any FGF5 are healthy, but are just super hairy; with fast growing hair and amazingly long eyelashes!”

All About Keratin

Aside from the live part of the follicle mentioned above and the pre-follicle stem cells, hair is essentially made of keratin – a hard structural protein.

The hair fiber has three distinct layers, which Dr. Burg describes. “The majority of the hair fiber is represented by the elongated keratinized keratinocytes: These hair cells form the cortex. The cortex is surrounded by different keratinized cells, which form the cuticle. Thick human hairs can have another cell type at their center, which form a structure known as the medulla. This is not present in all hairs, but is sometimes found in terminal hair”

biology of hair

 (Image courtesy of Dr. Burg)

While we’ve heard a ton about keratin, you probably are unsure of exactly what it is. “Keratins are a family of proteins whose role is to provide structure and rigidity,” says Dr. Burg, noting that proteins are the body’s building blocks and that DNA is actually a recipe that your body uses to build proteins. “The human genome codes for around 20,000 different proteins that have a variety of functions in the human body, from converting sugars to energy, to fighting disease, to making more proteins, “ he says. You might remember from actual bio that proteins are made from combinations of amino acids, of which there are 20 different types — of these, the various combinations of amino acids in different chain lengths gives rise to the huge diversity in protein shapes, functions and activities.

“There are 54 different types of keratin proteins and these have a range of different roles in the body,” he continues. The main role of keratin is to provide strength and structure to the skin, nails, and hair, and also in many different cell types in the body. In animals, horns are often made of keratins as well.

“One of the reasons keratin is so strong is because it contains a high amounts of the sulfur containing amino acid cysteine (human hair is ~14% cysteine). The cysteine forms very strong cross links with other cysteine amino acids (known as disulfide bridges), which helps give keratin its rigidity and strength. Keratin proteins in the hair have high numbers of helical structures with the disulfides bridging between the coils of the helices giving strength to the molecule,” he says.

 (Image courtesy of Dr. Burg)
The amino acid Cysteine, with the sulfur group circled in red (Left) and models of keratin 85 (right), one of the main hair cuticle keratins. Top right is a generalization of the helical structures and bottom right is the molecular ball and stick model

The Scalp’s Role in Hair Growth

The scalp is the environment in which the hair follicle organs are situated and scalp tissue acts as a media through which growth factors diffuse, allowing various cell types, such as immune cells, move around performing housekeeping duties and defense. “That scalp, as an extension of your skin, is the first line of defense against the environment and as such, can be impacted by the environment. Things like sunburn, harsh chemicals, pollution and our beauty routines can all cause changes in the scalp that lead to things such as imbalance in the microbiome and inflammation,” he explains.

This is where the microbiome comes in. The term microbiome refers to the ecosystem of microbes (bacteria, fungi and small creatures) that live on and in the human body.  A good balanced microbiome will out compete and fight off bad microbes, maintain a healthy pH and can actually work in concert with your immune system to maintain scalp and follicle health. However, imbalances in the scalp microbiome are known to be associated with dandruff, skin inflammation and seborrheic dermatitis. “Harsh chemical detergents or too frequent deep washing of the scalp with strong cleansers, can upset the microbiome, causing imbalance,” he confirms.

Like with most health issues, inflammation is using an underlying influence. “Inflammation is a generalized immune response to insult or injury,” says Dr. Burg. “Inflammation sets up a whole range of signaling and repair processes in the body.   When there is a low level of chronic inflammation, from repeated sunburn, use of harsh cleansers, heat styling, tight hairstyles and the like aberrant signaling can begin to occur in the hair cycle, resulting in hair cycle imbalance. In this way, inflammation and irritation of the scalp can impact the way that follicles grow and cycle, which impacts overall hair health,” he adds.

Hair Loss, Cause and Prevention

“Hair biology is complex, we actually know only a little about how hair grows, cycles, ages and why we experience hair loss,” continues Dr. Burg. “What we do understand is that at the center of it all: almost all forms of hair loss and hair aging; is shortening of the growth phase of the hair cycle. When the growth period becomes too short, hair falls out too quickly, excess shedding occurs, and the regenerating hair comes in finer and is less substantial.”

Recognizing hair loss is key. The first signs of an issue in women can be a widening of the part, more hair in the brush, or you may notice that your ponytail has become thinner. “For many women, a short growth phase also means they can’t grow their hair past a certain length, e.g. not past the shoulders. In men, increased hair in the shower, comb and on the pillow, as well as being able to see their scalp shining under bright lights are often signs that hair loss is occurring.”

“For men there is thought to be a strong genetic component of hair loss, but this is also quite complex and still relatively poorly understood, but some recent very large studies of the genes of men with early, severe hair loss have uncovered around 150 genes that appear to contribute to the problem, including the androgen receptor (which responds to Dihydrotestosterone – DHT) and other factors including the hair cycle regulator FGF5, and interestingly some genes involved in the metabolism of vitamin D,” he says. However, genes aren’t the only factor contributing to hair loss with things such as stress, poor diet, medications, severe illness/surgery also contributing and, with many men,  aging is also a strong contributing factor.   While hair loss in men can have a variety of contributing factors, the end result and process tends to follow the same path and also tends to occur over the same pattern, with the hair at the crown and front of the head being lost first.

Other Contributing Hair Loss Factors, According to Dr. Burg:

Hormonal changes – this can happen after and during pregnancy, when starting or changing contraceptive medication, or during menopause. Changes in hormone levels alter the body’s signals in truly profound ways, affecting many peripheral processes including the hair cycle.

Hereditary factors – some women have hair loss that runs in families, similar to the situation in men, the specific genetic factors associated with this are not well known or well-studied.  In men the situation is complex with >100 genes involved, and it is highly likely that hereditary hair loss in women is equally as complex

Diet – yo-yo or extreme dieting can lead to hair loss in many women, as the body shuts down hair growth to direct nutrients to the organs.  A balanced diet is critical for strong, healthy hair growth. It is important to maintain healthy levels of the B vitamins such as biotin, as well as Zinc, Iron, and vitamin E

Stress – extremely stressful events can result in hair loss. Generally, the stress levels have to be very high for the impact to be large, such as the death of a loved one, a divorce or bankruptcy. Stress promotes high levels of cortisol, which when combined with a “fight or flight” energy preservation strategy, can result in the body shutting down hair growth in favour of other organ functions.

Illness – any periods that put stress on the body can affect hair growth.  Similar to the situation in extreme dieting and stress, the body shuts down hair growth to preserve energy.  Treatments for cancer such as chemotherapy are well known to cause a temporary hair loss, but in many cases the hair will not grow back as strongly as before.  A special case for women is ongoing hormonal treatment following breast cancer.  These can cause ongoing hair challenges.

Separate to the issue of hair loss is hair greying. Hair greying happens as we age and as our hair goes through multiple cycles. As the hair cycles, falling and re-growing again, we gradually lose some of the special pigment producing cells known as melanocytes. Melanocytes produce two pigments, eumelanin (brown/black) and pheomelanin (red), which together account for all the different hair colors when combined in different quantities.   As we start to lose melanocytes, hair-by-hair, our pigmented shafts are replaced by grey ones. These hairs are not actually grey but clear/ colorless. Unfortunately, no one has worked out how to stop this process from happening.

A Lifetime of Hair Changes

Here’s what Dr. Burg wants you to expect from your hair as you age.


Hair will generally be at its best in the early 20’s where hair is cycling with a long growth phase and growing quickly. Hair shafts are thick, and cuticles are tight. Hair challenges can occur in your 20’s due to stress, for example college exams and break ups, dieting. Often, hair changes occur as a result of the contraceptive pill or active IUD’s, which all can interrupt the hair cycle, leading to increased hair fall, poor quality growth and thinning. Some men have a strong response to androgens at this age; these are thought to be a driver of difficult to treat early onset male hair loss.


Pregnancy, childbirth and breastfeeding change the hormones in the body, which can profoundly affect the hair cycle, leading to excess shedding and hair thinning. Pregnancy also affects the oil glands that lubricate and moisturize hair, with hair becoming more lustrous and beautiful during pregnancy, followed by a big change after childbirth where hair becomes dull and more brittle. Towards the end of the 30’s the hair follicles will also begin to get tired, grey hairs will start appearing and the hair may also start to thin out as the hair cycle changes. 


Hair shafts can become more brittle and prone to breakage, cuticles less tight and hair may also become dull. The associated coloring that many women regularly perform damages the hair further. In addition, hair follicles are becoming increasingly tired, more grey is appearing and thinning may become noticeable. By the time many women and men notice thinning at this point, they have already lost 30-50% of their follicles.


Hair growth rates decrease, hair follicles become more tired, and towards the middle and end of the decade, menopause often begins. These factors combine to result in a shorter hair cycle, more hair fall, shorter maximum length and dull brittle hair as the oil glands change their production. Many people are completely grey by this point, as their melanocytes have disappeared


In the decade of the 60’s menopause is complete; metabolism slows and with these there are more changes to the hair. With menopause comes a drop in the female hormones (estrogens etc.), leading to a relative increase in the influence of testosterone. Testosterone can affect women’s follicles in the same way as in some men, so a proportion of susceptible women will experience some hair loss due to this.   In the 60’s hair will also be noticeably more brittle and dry, hair fall may be increased and for some women their hair will be quite noticeably, thinner meaning that hair style choices change to cover up the effects; many men will notice a slow decline in the density and thickness of their hair

Hair SOS

Apart from choosing products that look after the hair cycle, prevent oxidative damage and nourish the follicles, such as the FGF5 blocking évolis range, there are a number of things that can be done to look after the hair, outlines Dr. Burg.

Eat a balanced diet: a balanced diet will be rich in B vitamins, Zinc, iron, and the other trace elements important for hair growth. After menopause, natural dietary sources of phytoestrogens such as flax seeds can also be beneficial

Get plenty of exercise: exercise boosts metabolism, which is important for rate of hair growth. Exercise also reduces stress levels, preventing stress hormones from shortening your hair cycle

Be kind to your hair: Avoid too many harsh chemical treatments. If you are going to wear extensions or weaves make sure that these are not too heavy. Heavy extensions can place traction stress on the follicles, leading to damage and potentially follicle death.

Use gentle naturally based cleansers: Natural is best! Avoid things like SLS and SLES, as well as parabens and silicones (often seen as dimethicone on the label), which can build up in the pores and cause further problems. Silicones can also weigh thinning hair down, which is not ideal. Ensure you are using products with natural antioxidants to fight the signs of aging. Also be careful not to wash too often as this can strip out the natural oils, resulting in brittle hair and breakages.

Scalp care is key to a lifetime of healthy hair. HERE’s how to treat yours.

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