The Biology of Hair – FolliQuest

Introduction

We all have a pretty accurate picture of what hair is:

It’s the collection of soft, fine, threadlike strands that grow on the top of our heads, and to whom we cling onto for dear life as soon as we notice the first, devastating signs of hair loss.

But what exactly is hair—scientifically speaking?

What it is made out of, how does it it grow, why does it fall out, and, most importantly: what are the strategies that we can employ to improve the health and longevity of our hair?

This article is a comprehensive guide on the science of hair growth and hair loss. We will cover important topics such as the hair growth cycle, the process of follicle miniaturization, and many other relevant topics that any man suffering from pattern hair loss should have a clear understanding of.

📝Table of contents

Anatomy of the hair

Hair is a little bit more complex than it first appears.

It is made out of two different components. One is biologically active, while the other is not. One is involved in the cause of baldness, while the other one is only showing its consequences.

We are talking about the hair follicle, and the hair shaft, respectively.

Hair shaft

The hair shaft is what we commonly refer to as hair. It is the visible part of the hair that is outside of the skin.

The hair shaft is primarily made out of a protein called α-keratin, the same molecule used by the body to produce nails. It has no vasculature or nerve endings and has no active biochemical processes going on. For this reason, it’s considered to be “dead” tissue.

A healthy, non-miniaturized hair has a thickness of 50–100 µm (0.05–0.1 mm). The shaft fiber is made out of three different layers:

Cuticle—a single layer of flat and thin cells that overlap (resembling roof tiles), which covers the entire hair shaft.
Cortex—the middle layer of the shaft. It is the thickest layer of the three, giving the shaft its mechanical strength. It also determines the hair color, since it contains melanin—the same molecule found in skin.
Medulla—the center of the hair fiber.

Due to its complete lack of biological activity, the hair shaft can be cut, shaved, dried, or styled using various products, without affecting its growth or the overall health of the hair.

It’s commonly believed that applying excessive amounts of conditioners on the hair could damage it and result in hair loss, or that shaving it would make it grow stronger—neither of these two beliefs have any scientific veracity and are demonstrably false.

The hair shaft can indeed be damaged by chemical products or heat, but as long as the scalp remains unscathed, none of these external treatments of the hair are going to affect its growth and overall health.

Hair follicle

The hair follicle is a tiny, elongated sac inside the skin that is responsible for growing the hair shaft, which is inserted into the follicle.

In men suffering from androgenic alopecia, protecting the hair follicles is of primary interest—since this is the organ that is being affected by follicle miniaturization.

Follicles undergoing this pathological process shrink and become progressively weaker over time. This, in turn, causes the hair to become thinner and weaker, until it gets to the point where it stops growing altogether, resulting in baldness.

Despite its tiny size, the hair follicle is a highly complex organ, with 20 different cells that play separate roles. It consists of four primary anatomical components:

Dermal papilla—a heavily vascularized structure at the base of the follicle, providing oxygen and nutrients to it.
The hair matrix, which surrounds the papilla—here is where keratinocytes proliferate and attach to the hair shaft, making it grow in length and thickness.
The root sheath—a multi-layered sheath that surrounds the follicle.
The bulge—located outside the root sheath, it houses a number of dermal stem cells, which are recruited for hair growth and skin repair.

The follicle has two other mini-organs attached to it:

The sebaceous gland that produces sebum—the oily or waxy substance which coats the hair and protects the skin
The arrector pili muscle—a tiny muscle that is capable of pulling the follicle towards the surface of the skin, causing goosebumps

In a healthy scalp, the base of the follicle is located in the dermal layer of the skin, at an average depth of 4 mm. The shape of the follicle will determine the texture of the hair—straight, wavy, or curly.

Unlike the hair shaft, the hair follicle is highly active biologically. It is well vascularized and has both muscle tissue and nerve endings. This is the reason why cutting hair does not hurt, but pulling it out of the follicle does.

The biological role of hair

In other mammals, that have their body covered with fur, hair plays a very important role in body temperature regulation, protecting the animal from extreme hot or cold temperatures, and water exposure, with the sebum on the hair acting as a water repellant.

In humans, which have a very low density of body hair, this role is mostly obsolete. The scalp hair might still be able to provide some level of protection against extreme temperatures and sun UV radiation—another reason to avoid losing your hair.

Although we’ve developed clothing and conquered the entire planet without hair’s protective effects as an insulator from the elements, hair still plays an important role in humans:

The eyebrows are critically important in communication, and the scalp and facial hair (or lack thereof) play a meaningful role in sexual attraction and social signaling—in both men and women.

For thousands of years, humans have attributed a great deal of importance to the aesthetics of hair: length, shape, and even color.

And this is still happening today, in modern times—the hair is used to signal a person’s social status, role in society, and even personal beliefs (think of the difference between the hairstyles of the past century’s rock bands vs. the strict grooming standards imposed in the military).

Hair is not only aesthetically relevant, shaping the head and framing the face, but it might also be indicative of your general health status. Many diseases can cause or worsen hair loss, and balding can make a young person look 5–10 years older than they actually are.

Androgenic alopecia, in particular, is associated with (but not causal of) an increased risk of developing cardiovascular and metabolic diseases later in life.

The hair growth cycle

Hair grows in cycles, consisting of 4 different phases:

Anagen—Active growth
Catagen—Active involution
Telogen—Resting phase
Exogen—Hair shedding

Fortunately, each follicle runs its own cycle, independent of the other follicles—this prevents the hair from falling out all at once when the cycle is completed.

1. Anagen

The anagen phase is the first and most important stage of the hair growth cycle. At this stage, the follicle presents high activity of keratinoid proliferation, causing the hair shaft to grow at an average of 1 cm (0.4 in) per month.

About 85–90% of the follicles are in the anagen phase and are actively growing hair.

In a healthy scalp, the anagen phase is very long, lasting for about 2–7 years. This enables the scalp hair to grow to extreme lengths—compared to the hair on the body (e.g. eyebrows’ anagen phase only lasts for a few weeks).

One of the ways in which androgenic alopecia affects the follicles, is the shortening of the anagen phase, stunting the growth of the hair.

Minoxidil, a very powerful hair growth stimulant, does the opposite: it lengthens the duration of the anagen phase and increases the percentage of hair follicles that are in this stage.

2. Catagen

Once the anagen phase is completed, the follicle undergoes a transitioning stage called catagen.

This is a very short stage, lasting for about 2–3 weeks, during which the hair follicle detaches from the blood supply, stops growing the hair, and instead creates a small keratin bulb at the base of the hair shaft.

This keratin bulb will enable the hair shaft to remain attached to the follicle during the next stage, the telogen (or resting) phase.

Since this is a very transient phase, only about 1–2% of the hair follicles are in the catagen stage of the cycle.

3. Telogen

During the telogen phase, the hair is no longer growing, but it’s not falling out either.

Using the tiny keratin bulb at the end of the hair (created during the catagen phase), the hair shaft simply remains anchored to the follicle for another 3 months, without doing anything. For this reason, telogen is sometimes referred to as the resting stage.

Under normal circumstances, about 10–15% of all follicles are in the telogen phase.

However, in people suffering from telogen effluvium—a condition which is often triggered by high levels of stress, psychological or biological—up to 70% of the hair follicles can simultaneously enter the telogen phase, causing massive shedding of the hair, 3 months following the traumatic event.

Minoxidil can induce this state for some of the people who are using it for the first time. But, fortunately, the shedding caused by minoxidil is temporary, fully reversible, and is actually a sign that the medication is working—since the hair follicles are positively responding to it.

4. Exogen

The exogen stage marks the end of the hair cycle. It simply means that the dormant hair falls out, making room for the brand-new hair growing beneath it. Following the hair shedding, the follicle will enter once again in the anagen (growth) stage, as the cycle begins anew.

In a healthy scalp, a person is expected to shed anywhere between 50–100 hairs a day. This is normal and is not indicative of any issues.

In men suffering from androgenic alopecia, the follicles shrink with each successive cycle, causing the hair to become shorter and thinner—a process referred to as miniaturization, which will be discussed in-depth in the next section.

Hair follicle miniaturization

Mechanism of action

The miniaturization of the hair follicles is a highly complex physiological process, which is associated with the reduction of the number of active stem cells in the follicle, and is one of the defining characteristics of male pattern baldness (androgenic alopecia).

The miniaturization process refers to the gradual shrinking of the hair follicles with each consecutive hair growth cycle.

In addition to becoming progressively smaller in size, follicles undergoing miniaturization also migrate upwards toward the surface of the skin. A healthy scalp follicle is normally located at an average depth of about 4 mm.

And finally, the third hallmark of follicle miniaturization is the shortening of the anagen (growth) phase of the hair growth cycle, which caps the maximum length of the hair.

Effects on the hair

The first visible consequence of follicle miniaturization consists of a general drop in the quality of the hair. The hair shafts become:

thinner in diameter
shorter in length
weaker and more brittle
less pigmented
their texture changes

As the miniaturization progresses over the years, the hair eventually gets to a point where it becomes too weak to penetrate the epidermis (top layer of skin), at which point the hair stops growing altogether, causing baldness in that area.

At this stage, the follicle becomes dormant—but may still be revived using stimulation therapy.

The final stage of follicle miniaturization is the death of the follicle and the formation of scar tissue around it—which is believed to cause the shining appearance of a bald scalp.

Many hair loss experts believe this to be the point of no return, after which only hair transplantation may be able to restore hair in the affected scalp area.

Timeframe and progression

Follicle miniaturization is not happening overnight. It’s a slow but steady process that gradually affects the follicles over the course of many years—or decades—starting as soon as the onset of puberty.

Hair miniaturization is not uniform. Not all follicles on the scalp are going to be affected to the same degree, all at once.

In men suffering from androgenic alopecia, the most vulnerable follicles are located at the temples and crown—this is where baldness starts, forming the well-known pattern in male pattern hair loss.

The age of onset and rate of hair loss is going to be different for every man. While some go completely bald in their 20s, others may see the first signs of hair loss when they are well in their 40s or beyond.

One of the clinical tools used in diagnosing and measuring the level of baldness is the Norwood scale—a 7-stage classification model used to determine the severity of hair loss.

Early initiation of treatment is strongly associated with better hair outcomes. Preventing further miniaturization is significantly easier than reversing the damage. Therefore, being proactive and taking action sooner is the winning strategy in the battle against hair loss.

Causes

Hair follicle miniaturization is a highly complex biological process that is not yet fully understood by science. There are, however, several factors that have been proven to trigger or exacerbate follicle miniaturization:

Genetics
Aging
High blood sugar levels
Oxidative stress
Scalp inflammation

However, in men suffering from androgenic alopecia, the main driver of follicle miniaturization is androgen-induced damage, primarily from DHT—a hormone that is synthesized in the scalp from testosterone, by the 5α-Reductase enzyme.

DHT plays such a critical role in the pathophysiology of androgenic alopecia, that lowering the levels of this hormone through medications (such as finasteride) has been shown to completely halt follicle miniaturization in most men—and in some cases, the damage was partially reversed, restoring the follicles back to a healthy state.

Strategies for maintaining healthy hair

Although follicle miniaturization in the context of male pattern baldness is primarily determined by genetics, there are a number of strategies that can mitigate the damage and protect the follicles.

Applied successfully, these strategies can stop or even reverse hair loss. Listed in the order of importance, they are:

Stopping the DHT-induced damage
Using stimulation therapy
Optimizing the scalp microbiome
Controlling high blood sugar levels
Cessation of smoking or vaping
Managing stress
Supplementing vitamins and minerals

1. Stopping the DHT-induced damage

The first and most important item on the list is stopping the damage caused by androgens—and DHT in particular.

The gold-standard medical approach employed by millions of men worldwide is the inhibition of the 5α-Reductase enzyme by using finasteride. This enzyme is required for converting testosterone into DHT, and, therefore, blocking it would lower the levels of DHT to a tolerable threshold, enabling the follicles to thrive.

2. Using stimulation therapy

Once the damage has been mitigated, stimulation therapy can be employed to encourage new hair growth. Listed in the order of effectiveness, stimulation therapies include:

Topical minoxidil
Microneedling
Platelet-rich plasma injections (PRP)
Low-level laser therapy
Scalp massages (not backed by science)

3. Optimizing the scalp microbiome

Another strategy for maintaining the health of the follicles is to maintain the health of their environment—the scalp.

The most commonly used medication for this purpose is the ketoconazole shampoo. It has a triple effect: it lowers inflammation in the scalp, keeps the scalp microbiome under control, and also disrupts the local metabolism of DHT, acting as a mild local anti-androgen.

In addition to its hair loss prevention benefits, the ketoconazole shampoo is also a great anti-dandruff agent. Due to its ease of use and excellent safety profile, it’s one of the first products added to a hair loss prevention protocol.

4. Controlling high blood sugar levels

Having diabetes, hyperinsulinemia, or being otherwise metabolically compromised is one of the key factors that negatively affect the progression of many conditions—including the miniaturization of hair follicles.

Keeping the blood sugar levels under control through regular exercise and dietary changes is not only going to aid your follicles, but it’s going to make a profound impact on your overall level of health.

5. Cessation of smoking or vaping

Smoking is demonstrably one of the worst things you can do for your health. It also directly causes damage to the hair follicles by means of DNA damage and increased levels of oxidative stress.

Vaping, although considered by many a healthier alternative, is not that much better when it comes to follicle health, even if there is no smoke involved. Consuming nicotine—in any shape or form—is going to damage the tiny blood vessels in the dermal papilla that supply the follicles with oxygen and nutrients.

Cessation of smoking, vaping, or any other nicotine products may be difficult, but it’s a lifestyle adjustment that is worth doing—both for your hair and your overall health.

6. Managing stress

Undergoing high levels of chronic stress is a known risk factor in many conditions, including cardiovascular diseases, metabolic disruption, autoimmune diseases, premature aging, and, of course, hair loss.

High levels of stress are known to cause telogen effluvium—a hair loss condition in which the follicles prematurely enter the telogen phase, causing a large amount of hair shedding a few months later.

Considering the devastating effects of stress in telogen effluvium, it’s not too big of a stretch to assume that it may also negatively impact the progression of male pattern hair loss.

7. Supplementing vitamins and minerals

Hair is non-essential for survival. It does not serve any vital function. Therefore, if there is any nutrient deficiency in the body, the hair is one of the first things to be deprioritized.

Being deficient in certain nutrients is known to cause the hair to become weaker and thinner—which is the last thing that you want happening if you are already suffering from underlying male pattern hair loss.

Adopting a well-balanced, nutrient-rich diet should be the first option for optimizing the levels of nutrients in the body. In addition to the diet, some people might improve their hair health by supplementing with:

Vitamins A, C, D, and E
Biotin (B-7)
Folate (B-9)
Cobalamin (B-12)
Magnesium
Zinc
Iron
Collagen

It’s important to note that while ensuring proper nutrition will improve both hair and overall health, none of these supplements are going to stop the progression of male pattern baldness if the underlying cause of the condition is not addressed first.

Conclusion

Hair is made out of biologically inactive fibrous proteins called keratins. It does not play any vital biological role in humans but is still relevant in communication and social signaling.

The visible hair on the scalp is produced by a tiny organ inside the skin called the hair follicle, and it grows in cycles consisting of four distinct phases (anagen, catagen, telogen, and exogen). Once a cycle is finished, the old hair falls out and is replaced by a new one as the cycle begins again.

The hair follicle is highly vulnerable to a number of biological stressors, including oxidative damage, high levels of blood sugar, and, in the case of men suffering from androgenic alopecia, DHT—a derivate of testosterone.

In male pattern baldness, the follicles undergo the process of miniaturization—the progressive shrinking of the follicle, which over time results in thinner and weaker hair, and, eventually, in the balding of the affected area.

There are a number of strategies that can be used to combat and reverse hair loss, including mitigating the DHT-induced damage through 5α-R inhibition, applying minoxidil or using other hair growth stimulants, lowering the inflammation of the scalp, managing stress, and adopting a nutrient-rich diet or supplementing any potential deficiencies that might have otherwise exacerbated hair loss.

🔬Scientific References:

Martel JL, Miao JH, Badri T. Anatomy, Hair Follicle. [Updated 2022 Oct 10]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-.

⚠ Disclaimer: This article does not constitute medical advice and is intended for general informational purposes only. The information in the article is not a substitute for and should never be relied upon for professional medical advice, diagnosis, or treatment. Always discuss with your doctor if you have any questions. Please read our Medical Disclaimer.