The Science of Healthy Hair, Hair Loss and How to Regrow Hair

The episode opens with Andrew Huberman, a professor of neurobiology and ophthalmology at Stanford School of Medicine, setting out the topic: hair, and what science has shown about slowing or even reversing hair loss. The host frames the research as interesting mainly for its cellular biology. Hair connects to stem cells and to development, a subject the host has long studied in the nervous system, where a small batch of cells multiplies into many trillions through the cell cycle and mitosis.

every hair, every single individual strand of hair, has its own little stem cell niche

This niche is a small pocket in the follicle where specific stem cells produce a hair for a set length of time, which depends on the hair and its location on the body. Scalp hair is described as growing continuously for four to six or even eight years if left uncut. Eyebrow hair grows for a period on the order of months. The episode uses that contrast to explain why eyebrows never reach the waist while uncut scalp hair can. Hairs themselves are described as "simply proteins of varying length," and the central question becomes what determines how long a hair keeps growing before it stops and falls out.

The planned scope covers what regulates these stem cells. It then turns to hormone-related hair loss in men and women, mechanical and stress-related influences, and chemical and mechanical treatments. The host lists minoxidil, dutasteride, ketoconazole, microneedling, and the thyroid, estrogen and IGF-1 pathways, and promises explanations that do not assume a biology background.

The first myth addressed is that balding patterns are inherited from one's mother's father. The host says this is not true. People do inherit genes that affect their predisposition to balding in particular parts of the head, and even particular parts of the body. But a photo of one's maternal grandfather at age 50, 60 or 75 cannot predict that exact pattern of hair loss. More myths about hair loss, replacement and regrowth are promised for later. The host also notes that the podcast is separate from their teaching and research roles at Stanford and is meant to provide zero-cost science information to the public. A sponsor read for NFL coverage on ESPN and the ESPN app follows.

After talking with experts on hair biology and on halting and reversing hair loss, the host stresses that hair has a strong psychological side as well as an interesting biology. Most people who experience even marginal hair loss are said to undergo fairly severe anxiety. The host, 47 at the time, says they cannot personally relate. They describe a couple of thin patches at the front of their scalp and suggest this reflects a higher density of DHT (dihydrotestosterone) receptors at those spots, a point the episode says it will explain later.

A childhood anecdote shows how stress and hair are linked in popular belief. The host's father, trying to calm them before sleep, told a story about a cousin who went to bed stressed and woke to find all his hair on the pillow. The host says plainly that they don't know whether the story is true and could not verify it with their father. They still affirm the general point that psychological well-being can affect both hair coloration and growth rates. The relationship also runs the other way: thinning, shedding or color change can bring intense anxiety or even depression.

The host says they had not appreciated this distress, perhaps because they have always kept their hair short and assumed they would shave their head if it really fell out. They recognize that most people would hate to lose their hair, citing the large amount of money spent on treatment, which they estimate loosely as probably in the high billions. The figures given are that by age 50 roughly 50% of men and women have noticeable hair loss, and up to 85% of those experience anxiety that leads them to seek treatment.

The host clarifies that age 50 marks when people notice the loss, not when it begins. Loss is described as ongoing from about age 30 to age 50. It is often spotted under bright bathroom or mirror lighting that shows through the outer layer of hair and reveals thinning in one area. The two-way link between mental state and hair growth, loss and graying is restated as a reason the topic draws so much attention.

The host introduces a theme that recurs through the episode: hair loss can be addressed by mechanical and by chemical approaches. Understanding the underlying biology is presented as the way to see why some treatments work better than others and why some carry side effects while others carry none. Mechanical approaches range from scalp massage to microneedling. The episode notes that mechanical changes to the scalp can either cause hair loss or help hair grow.

Chemical approaches rest on hormonal regulation. Hair growth is described as strongly regulated by estrogen, thyroid hormone and insulin-like growth factor. Androgens, meaning testosterone and especially derivatives such as dihydrotestosterone, are described as setting the stage for growth by controlling how large or small the pool of hair-producing stem cells is.

The host separates two meanings of "stem cells." Exogenous stem cells come from outside the body and are what people inject into the face, scalp, joints or muscles. The episode concerns endogenous stem cells, which the body makes itself and which can give rise to other cells, the defining property of a stem cell. Stem cells are present from conception, when the fertilized egg begins duplicating. Once the body plan is complete, many stem cell populations disappear. The brain, for example, gains few new cells past puberty, and probably earlier, because it has few stem cell populations. Other tissues keep pockets of stem cells throughout life, and hair is one of them. Every hair exists because a stem cell population is producing it.

Looking closely at a single hair, the root lies below the skin in a narrow trench in the epidermis, and the shaft is the visible part above the surface. At the base of the root is a small round chamber, technically called the hair bulb. In the bulb, stem cells, also called progenitor cells, divide by mitosis to produce daughter cells, which become the various cells that make up the hair. A hair is therefore born in the bulb and grows by stacking up from below. It is made of keratin proteins, which come in several kinds and bind together strongly. The host points to how hard it is to tear a thick hair as evidence of that tensile strength.

The bulb also contains cells that produce melanin, the pigment that darkens hair. Except in the rare albino mutation, where hairs lack all melanin and are truly white, most people have some melanin in their hair. The source describes melanin as "just a protein" that is essentially injected into the keratin. The host flags pigment as relevant to anyone interested in reversing graying.

Next to every hair root, in the dermis below the epidermis, sits a sebaceous gland that produces an oily substance called sebum. The host acknowledges the name sounds unpleasant but describes two important functions. First, sebum seeps around the hair as it moves from root to shaft and forms a seal where the hair exits the skin. The episode credits this seal with an important part of the skin's waterproofing, alongside the dense packing of skin cells. Second, sebum is described as a strong antibacterial and antimicrobial agent that forms an immune boundary against infection at the hair root. The host flags sebum for later discussion in relation to psoriasis and to fungal causes of hair loss.

The arrector pili muscle runs diagonally from around the bulb, or slightly above it, up to the skin surface. It contracts in cold or fear and pulls the surface skin down around the follicles. This produces goosebumps: the bumps mark where micro-hairs sit, and the dimples between them form where the muscle pulls down. The contraction makes hairs stand up, which the host connects to the phrase about being so frightened one's hair stood on end. In the cold, raised hairs trap air that the body warms. The host says this effect is stronger in very hairy people than in those with light body hair, and uses Huskies in snow as an example of a blanket formed by hair, air and skin. The host says the muscle does other important things that will come up later in the episode.

Recapping the structure, the host adds one more element: capillaries that reach into the bulb and support both the stem cells and the melanin-producing melanocytes. These vessels deliver nutrients and also oxygen, because growing hair is described as a very active process.