andrew huberman on hair loss and hair growth

The human body is a fascinating and complex system continuously demonstrating its ability to regenerate and heal itself. One of the most remarkable examples of this process can be found in hair growth. Hair stands out as an exceptional example of cellular and stem cell improvement, with each hair follicle containing its stem cell niche that allows for varying periods of growth. Understanding this process highlights the incredible regenerative capabilities of the human body.

The hair growth pattern, known as the anagen phase, can last between 4-6, even up to eight years. However, it’s important to note that hair growth patterns vary across different body parts. For instance, eyebrows tend to grow shorter than scalp hair due to the components of proteins of varying lengths, hair follicles, and stem cells.

This post aims to provide you with a constructive understanding of hair growth. We’ll delve into how hair biologically grows and what regulates stem cells in hair follicles to promote hair growth.

Keep reading to learn more about this fascinating aspect of human biology along with a review of Andew Huberman’s The Science of Healthy Hair, Hair Loss and How to Regrow Hair.

Psychological States & Hair

Most people who experience hair loss have severe anxiety, which shows how stress affects hair growth and, in turn, how anxiety triggers hair loss. Stress is a significant factor that may inhibit hair growth and even lead to hair loss. The hormone cortisol is made by the body when it is under stress. High cortisol levels can mess up the normal hair growth cycle, sending hair into the resting (telogen) phase too soon, which can eventually cause it to fall out.

A condition called telogen effluvium can happen when a lot of hair follicles enter the telogen phase at the same time. This causes a lot of hair to fall out. This is usually only a short-term problem, but hair can take a few months to grow back to its average rate.

hair anatomy stem cells

Hair Anatomy & Stem Cells

Now that we know the psychological aspect of stress and hair growth let’s get into the details of the structure of hair and stem cells.

Stem cells are present even when we are in the womb. These cells have an exceptional potential to give rise to many different cell types in the human body. For instance, stem cells can address and transform to cells at wrinkles, improve skin quality, increase hair growth on the scalp, or aid in healing injured joints or muscles.

Each hair strand has a unique stem cell responsible for its growth and development. These stem cells produce daughter cells that eventually grow into the hair. Conversely, the hair shaft is made up of a fibrous protein known as keratin.

The color of hair is determined by the amount of melanin it contains. Melanin is produced by melanocytes and transferred to hair keratin to produce dark hair. In the case of an Albino mutation, there is no melanin production, resulting in white hair. The sebaceous gland produces antibacterial sebum and waterproofs the skin, protecting it from microbes.

The arrector pili muscle between the hair bulb and the skin surface plays a crucial role in hair growth. When contracted due to cold or fear, it causes goosebumps. This muscle can also cause hair follicles to stand up, known as piloerection, which aids in body cooling during cold weather.

3 Phases of Hair Growth

3 phases of hair growth

Hair follicles, like other cells in the body, have a growth cycle; they’re divided into three stages: anagen, catagen, and telogen.

These stages determine the lifespan of each hair follicle. For hair growth, the follicles require essential elements such as sufficient oxygen, blood supply, stem cells, and the proper hormonal signal to stimulate development. The follicles can enter the anagen phase and grow if these elements are present. In some cases, specific hairs may even re-enter the growth cycle and return to the anagen phase. However, the absence of hormonal input activates the telogen phase, which leads to hair loss.

Let’s delve into each stage of hair growth deeply!


During the first phase of hair growth, known as anagen, the stem cells dive into the bulb, giving rise to the cells that make up hair proteins, leading to actual growth. It’s important to note that hair grows from the bottom to the top, which means it grows from deep within the root, stacks up, and eventually extends throughout varying durations, depending on which hair is in the body. For instance, for scalp hair, the anagen phase takes 2-8 years on average, a significantly long period for hair growth.


The Catagen phase, which is also known as the transition phase, is a catabolic stage during which the hair recedes from the bulb region towards the skin surface and ultimately into the root. The duration of this phase varies among individuals, depending on various factors.

During this phase, there is an internal recession of hair which is a crucial phenomenon as it involves modifying the bulb region. Typically, an interface exists between the stem cell population, melanocytes, and hair, which mutually support each other. This interdependence is essential for the proper functioning of the hair growth process.

Notably, the area receives nourishment from blood vessels, which are vital in supplying the necessary nutrients for hair growth. Therefore, it is essential to maintain a healthy blood flow to ensure optimal hair growth during the Catagen phase.


The telogen phase, the final stage of the hair growth cycle, is characterized by a period of rest. During this phase, stem cells do not produce new hair proteins, and the bulb at the hair follicle’s base begins to constrict and detach from the surrounding tubes that connect to the skin surface.

This process ultimately leads to the detachment and death of the hair follicle, resulting in the loss of stem cell population and melanocytes. Put simply, during the telogen phase, the population of stem cells that generate new hair and melanocytes responsible for hair pigmentation are depleted, resulting in the absence of hair in that area.

Additionally, scalp hair undergoes a process of re-entry into the cell cycle, returning to the anagen phase and growing back.

Scientific Approaches to Promote Hair Growth

Increase Blood Flow

Proper blood circulation is necessary for healthy hair growth, delivering vital nutrients and oxygen to the hair follicles. In contrast, poor blood circulation can lead to inadequate nutrition and a shorter anagen phase, resulting in short and brittle hair strands.

Fortunately, there are ways to promote blood flow to the scalp, which can help reduce hair loss and promote longer healthier hair. By exploring ways to enhance blood flow to the scalp and determining their effectiveness, you can take proactive steps toward promoting healthy hair growth.

Minoxidil & Blood Flow

Effective hair growth hinges on robust blood circulation, supplying vital nutrients to hair follicles. This is pivotal in understanding treatments for hair loss prevention, exemplified by minoxidil, also known as Rogaine. Initially an antihypertensive medication, minoxidil extends the anagen phase of hair development, slowing hair loss onset.

To manage side effects, doctors commence minoxidil treatment with a lower dose, gradually increasing it. However, the association between minoxidil and heightened prolactin levels is an important consideration. Dopamine, a neuromodulator, and the pituitary gland hormone, acting as an antagonistic neurotransmitter, contribute to potential side effects like decreased libido. Elevated prolactin levels also pose the risk of gynecomastia, the enlargement of male breast tissue.

Minoxidil can be administered topically or orally to address hair loss. Oral doses range from 0.25 to 5 milligrams daily, while topical application involves a 5% concentration applied once daily. Despite the common belief that minoxidil solely impacts the scalp, topically applied 5% minoxidil can enter the bloodstream, causing systemic effects. Notably, the topical use of minoxidil does not mirror the mechanism of oral ingestion.


While the effect is temporary, incorporating scalp massage into your daily routine can promote blood circulation, which has been suggested to reduce hypertension by dilating blood vessels and capillaries. This, in turn, can help promote hair retention. Although it may not entirely stop or reverse hair loss caused by genetics, regular scalp massage may help slow down the process or maintain your existing hair. Give it a try and see if it works for you!


Originally developed as a drug to treat prostate health issues, Tadalafil increases blood flow to the prostate and counteracts some of the problems associated with an aging prostate. Its mechanism of action involves improving blood circulation to the stem cell microenvironment, which in turn promotes hair maintenance. Although Tadalafil may not be effective in reversing hair loss, using low doses to slow down hair loss can be considered a logical mechanistic approach, similar to the rationale behind using minoxidil to mitigate hair loss rates.

The primary objective of using Tadalafil is to improve blood circulation to support the stem cell microenvironment beneath the hair follicle. By augmenting blood circulation to the stem cell microenvironment, Tadalafil promotes hair maintenance, but it does not reverse hair loss. However, using low doses of Tadalafil to decelerate hair loss can be viewed as a logical mechanistic approach.

Platelet-Rich Plasma (PRP)

Platelet-Rich Plasma (PRP) therapy is an innovative technique to enhance nutrient delivery to a specific body area using an individual’s platelets. This process is a safe and effective way to improve nutrient transportation to targeted body regions. The procedure involves drawing a small amount of blood from the individual, which is then separated via centrifugation to isolate different blood components. The platelets are then carefully separated from the other components and are reintroduced into the bloodstream via a solution.

The fundamental principle of PRP therapy is to stimulate the enrichment of an individual’s platelets with various nutrients, promoting nutrient transportation to a specific part of the body. This technique is also used for hair loss treatment, and it has demonstrated moderate effectiveness. Although PRP hair injections can be costly, they are a worthwhile investment for individuals seeking to improve nutrient delivery to specific areas of their body.


Microneedling is a treatment that involves using multiple tiny needles to mechanically stimulate hair follicles and the stem cell niche on the scalp. The needles can be arranged in a stamp-like configuration or integrated into a roller. These needles can range in length from 0.5 to 2.5 millimeters and may cause some discomfort to the skin.

There are two primary purposes of microneedling. Firstly, research has shown that it can reactivate a semi-quiescent population of stem cells in the telogen phase, promoting hair growth. Secondly, it can induce cellular changes in hair follicles with PRP injections. These treatments can stimulate the reactivation of stem cells and telogen phase follicles that contain melanocytes and partially dormant stem cells, enabling them to reenter the cell cycle.

All these treatments, whether they involve medication or needling, share a common goal of enhancing blood circulation in the targeted area.

Microneedling, Minoxidil & “Dead Zones”

Microneedling is a widely used technique that has shown positive results in people of all ages and genders, especially when combined with other therapies. Needle lengths ranging from one millimeter to about 2.5 millimeters have proven more effective than shorter needles. Microneedling involves inducing bleeding in the scalp to stimulate hair growth. While some people may experience discomfort, it is still a commonly utilized technique. It physically disturbs the scalp skin, which leads to bleeding and inflammation.

Combining microneedling with minoxidil has resulted in better outcomes than using either treatment alone. This combination is particularly effective for restoring “dead zones,” areas of complete or near-complete baldness that lack a stem cell population. The combination has been observed to help recover stem cell populations, thereby enabling new hair growth. However, it is essential to remember that hair may take 30 to 50 weeks to grow in these “dead zones.” Neither Minoxidil nor microneedling alone has been found to stimulate stem cell proliferation in “dead zones,” but their combination has been found to do so.

Botox Treatments

Although Botox is being explored as a treatment to stimulate hair growth, utilizing botulinum, a bacterial toxin, its effectiveness in treating hair loss remains to be determined due to limited studies. This neurotoxin cleaves proteins in neurons, hindering neurotransmitter release and inducing muscle paralysis when injected. When Botox injections are administered in the scalp, they relieve tension, improving blood flow and activating hair follicle stem cells. However, caution is essential, and qualified professionals must administer injections to prevent adverse effects like eyelid drooping since Botox’s effects are temporary, necessitating repeated treatments.

An alternative to minoxidil, Tadalafil, enhances blood circulation with fewer side effects. Despite its invasiveness, some opt for Botox treatment for scalp-related conditions like cutis vertices gyrate, which is linked to hormonal imbalances and alopecia.

Androgens, Hair Growth & Pattern Hair Loss

Androgens, such as testosterone and dihydrotestosterone, exert inhibitory effects on IGF-1 and cyclic AMP activity. DHT, derived enzymatically from testosterone by 5-alpha reductase, exhibits a five-fold higher binding affinity to androgen receptors than testosterone, conferring greater androgenic potency. DHT is pivotal in physiological processes, impacting mental and physical vigor, libido, and strength.


Testosterone levels peak during youth in both males and females, gradually declining with age. The aging process sees an increase in five alpha-reductase activity, leading to heightened conversion of testosterone to DHT. DHT impedes hair growth by reducing IGF-1 and cyclic AMP levels. Hair loss patterns vary; some experience thinning in the crown and back, while others face recession in the frontal, flank, or midline regions. These variations stem from genetic and androgen receptor disparities. The inheritance of androgen receptor patterns is a significant factor.

In summary, androgens like testosterone and DHT influence IGF-1 and cyclic AMP activity, with DHT’s higher androgenic potency impacting physiological processes. Testosterone levels peak in youth, decreasing with age due to increased five alpha-reductase activity. DHT, derived from testosterone, hinders hair growth by reducing IGF-1 and cyclic AMP. Hair loss patterns are genetically determined, with androgen receptor inheritance playing a crucial role.

Scalp vs Beard Hair

The main difference between scalp and beard hair is closely connected to androgen receptors. These receptors react to androgens, especially dihydrotestosterone (DHT), a hormone linked to male traits. Notably, the androgen receptors on the face guide beard growth. Interestingly, how many receptors you have on your face affects how thick your beard becomes. As you age and DHT levels rise, it creates conditions for a rich and fuller beard. This interaction between androgen receptors and hormone levels reveals the interesting biology behind why hair grows differently on the scalp and beard.

Topical Caffeine & Slowing Hair Loss

Caffeine has many effects besides keeping you alert by stimulating the central nervous system. One of these effects is that it acts as a potent inhibitor of PDE. By inhibiting PDE, caffeine indirectly stimulates IGF-1, which PDE can suppress.

When applied topically in ointment or cream to the scalp, caffeine can suppress PDE enough to increase IGF-1 and promote hair growth. At the very least, it can maintain hair growth in that area.

Compared to Minoxidil, caffeine has fewer adverse side effects. For instance, it does not reduce blood pressure or potentially increase prolactin.

Although some clinical studies explore topical caffeine treatment for hair loss, they are less extensive and numerous than the studies on Minoxidil. This is because caffeine-based treatment has not been around for as long.

It’s worth noting that the concentration of caffeine in different ointments may vary. Furthermore, most studies on caffeine’s effect on the stem cell niches that control hair growth and the extension of the anagen phase of hair growth have been conducted in vitro.

If you decide to use caffeine ointment, applying it every day is unnecessary. Using the ointment three times a week should suffice. Given its effectiveness, caffeine as a topical treatment for hair loss is a good choice in terms of cost and side effects.

IGF-1: Growth Hormone & Sermorelin; Insulin Sensitivity: Myo- Inositol

Boosting hair growth often involves increasing a substance called insulin-like growth factor 1 (IGF-1) using growth hormones. Sermorelin, a type of peptide, is effective in raising growth hormone levels, which, in turn, increases IGF-1. However, it’s crucial to know that both growth hormone and IGF-1 can have side effects, like promoting tissue growth and potentially causing issues like small tumors and a higher risk of cancer. Sermorelin helps indirectly increase IGF-1 levels, encouraging hair growth, and works best when combined with other treatments.

IGF-1 production in the body depends on insulin, which is why it’s insulin growth factor one. This connection affects things like hair follicles and stem cell activity. So, it’s important to keep insulin sensitivity high and avoid insulin resistance. People dealing with obesity or type 2 diabetes, a sign of insulin resistance, should address their condition. There are prescription options, like GLP-1, showing promise in this regard. Obesity is linked to hair loss, and certain supplements like myoinositol, taken at around 900mg before bedtime, may help. Berberine and metformin are also known for improving insulin sensitivity. Understanding and addressing these factors can better support the natural processes that contribute to healthy hair growth.

Iron & Hair Growth

To ensure optimal hair growth, it is essential to recognize that iron and ferritin are vital components in the cellular growth pathways. These pathways extend from stem cells, stimulating keratin production within the hair. It is crucial to be mindful that an excessive iron intake may result in toxicity, while inadequate consumption can lead to anemia. Therefore, it is recommended to maintain a daily iron intake ranging from 25 to 100 milligrams for females and 30 to 150 milligrams for males. To maintain adequate iron levels, consider incorporating supplements or dietary modifications. By doing so, not only will you mitigate the effects of iron deficiency, but you will also support healthy hair growth during the anagen phase.

5-Alpha Reductase & Saw Palmetto; Curcumin

DHT has been found to shorten the anagen phase, a significant cause of hair loss. However, some interventions can be implemented to counteract this negative impact. By targeting 5-alpha reductases to lower DHT levels, we can help sustain the anagen phase and prevent the onset of the telogen phase. One promising intervention that can inhibit 5-alpha reductase is saw palmetto derived from palmetto berry.

It is effective in retaining hair and potentially stimulating new follicle growth. While it may not be effective in reversing hair loss, it is affordable and widely available, making it a noteworthy option. In addition, certain herbal compounds, such as green tea extract, racy mushroom, pumpkin oil, zinc, and curcumin (turmeric), have been suggested to support hair growth.

Although determining the optimal components and dosages in these formulations can be challenging, these compounds have been found to work together in promoting hair growth. Curcumin, in particular, acts as a potent inhibitor of 5-alpha reductase and DHT in specific individuals.

Ketoconazole & Offsetting Hair Loss

Ketoconazole is a chemical compound that has been scientifically shown to stimulate hair growth. It was initially developed as an anti-fungal agent to treat dandruff and psoriasis. Nizoral is a popular brand of shampoo that contains ketoconazole. Research has demonstrated that the use of ketoconazole can increase hair count and thickness. However, one of the potential side effects of using this treatment is dryness, thinning, and brittleness of the hair. The mechanism of action of ketoconazole is intriguing as it impedes certain fungal growth on the scalp.

Ketoconazole is an antifungal agent that enhances the sebum’s ability to prevent other fungal infections. This leads to a slight decrease in dihydrotestosterone (DHT) levels. The recommended application of ketoconazole shampoos is two to four times per week, with a scalp contact duration of approximately three to five minutes. This has demonstrated an 80% success rate in preserving hair that would otherwise be lost. However, the efficacy of ketoconazole in promoting hair regrowth remains uncertain.

If you are considering using ketoconazole to mitigate hair loss, it is important to acquire a shampoo containing a minimum of two percent concentration of ketoconazole. Some hair products available in the market contain only 1%. It is also worth noting that ketoconazole may cause side effects such as mild scalp irritation, hair thinning, and brittleness.

Topical & Oral Finasteride

Finasteride is a medication that promotes hair growth by inhibiting 5-alpha reductases and reducing DHT levels. It works by targeting the type 2 isoenzyme, which effectively lowers DHT and increases hair count by 20%. It also reduces hair loss by 50% and enhances thickness by 20-30%.

Finasteride is available both topically and orally in a 1% solution. Initially, it was used for age-related prostate enlargement before becoming a topical solution. The dosage varies from 0.01 to 5 mg, with a logarithmic distribution revealing a 50% DHT reduction at 0.01mg. There is a gradual, nonlinear trend from 0.2mg to 5mg.

While reducing DHT may lead to adverse effects such as sexual side effects, concerns arise with low doses, which yield DHT reduction without immediate visible changes. Topical 0.25% Finasteride equals oral 2.5mg and stimulates new hair growth at a blood concentration of 0.2 mg while preserving existing hair.

The relationship between dosage and side effects is positive, meaning heightened sensitivity is observed. Professionals recommend taking 0.5-1mg orally, which is well-tolerated and effective. It’s important to have patience as escalating dosage without observable hair growth is unwise.

Topical Finasteride has fewer adverse effects than oral, with studies reporting 30-50% fewer severe side effects. Ultimately, while Finasteride has its benefits, it’s essential to consult a healthcare provider before using it and to be aware of the potential side effects.

Post-Finasteride Syndrome

There is a potential connection between taking the standard five-milligram daily prescription of finasteride for prostate issues and an elevated risk of developing Post-Finasteride Syndrome. Although this syndrome has been used for a long time, initial discussions about it were limited.

When men decide to stop taking finasteride, whether it’s for prostate or hair loss, they may experience a condition known as Post Finasteride Syndrome. This can occur even if they were taking doses ranging from one to five milligrammes daily. There are certain symptoms that individuals may experience, such as a decrease in libido, difficulties with erectile function, and feelings of depression. These symptoms often lead individuals to seek medical assistance.

Post Finasteride Syndrome may be more likely to occur in younger men who use higher doses of finasteride for hair growth. It’s worth noting that there is a higher prevalence among men in the age range of 20 to 30.

Upon closer examination, it becomes evident that dihydrotestosterone plays a crucial role in the early stages of embryonic development, particularly in the formation of male genitalia. The discovery of post-finasteride syndrome has led to a reevaluation of the wider impact of dihydrotestosterone on male maturation, including its potential influence on hypothalamus development. It is crucial to have a more comprehensive grasp of how it affects both physical and mental development.


Dutasteride is a chemical compound similar to finasteride and is known for its remarkable potency in effectively suppressing all three variants of the alpha-reductase enzyme. The standard dutasteride dosage ranges from 0.5 mg to 2.5 mg and is administered orally. This compound is noteworthy for its efficacy in promoting hair growth and reducing DHT levels by 90%, which is higher than the efficacy of finasteride. Furthermore, dutasteride exhibits an onset of action that is two to five times faster than finasteride.

However, dutasteride has a downside as well as its efficacy. It may cause a range of adverse effects linked to the DHT pathway, such as a reduction in libido and motivation. It may also disrupt other physiological pathways, such as elevated estrogen and prolactin levels, and, in some cases, it may induce the growth of male breast tissue.

Which One Is The Best Mechanical & Chemical Stimulation for Hair Growth?

Since combination therapies leveraging chemical and mechanical stimuli have proven more effective than relying on a singular stimulus, micro-needling stands out as a highly effective mechanical stimulus. When paired with finasteride, micro-needling demonstrates remarkable results in promoting hair regrowth, even in individuals experiencing baldness. This synergistic approach holds great potential for achieving substantial hair regrowth.

However, exercising caution is paramount when combining treatments that inhibit the DHT pathway, as excessively reducing DHT levels should be avoided. These treatments can elicit varied responses from individuals. Therefore, to mitigate potential adverse effects, initiating the regimen with a lower dosage is advisable. This approach aims to minimize the negative impacts of the medications while optimizing the therapeutic outcome.

Furthermore, consideration may also be given to incorporating ketoconazole shampoo or saw palmetto into the regimen.

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