Dr. Andrew Huberman, Ph.D. is a Professor of Neurobiology and Ophthalmology at Stanford University School of Medicine. His lab focuses on neural regeneration, neuroplasticity, and brain states such as stress, focus, fear, and optimal performance.
Andrew Huberman explains the biology of hair, hair growth, why hair growth slows, and what causes it to fall out.
All about hair
- Different hairs on your body have different lengths of growth phases (for example, hair on the head will grow for 2-8 years, and hair on the eyebrows will fall out every few months)
- The rate of hair growth is relatively stable across hair – what differs is the length of the growth phase
- Microneedling procedures, PRP injections, and Minoxidil all center around the general idea of increasing blood flow, increasing oxygen and delivery of nutrients, or increasing inflammation just enough locally to set off a cascade of regrowth
- Combination treatments that combine a mechanical stimulus (such as microneedling) with chemical stimulus (such as minoxidil) will always be better than either alone
- But be realistic, it’s unlikely to grow a full head of hair again if you are bald
Why hair grows
Three phases of the hair growth cycle:
Anagen phase: stem cells in the bulb give rise to proteins that make up hair; hair grows deep within the root and up through the skin
The growth phase varies depending on location – hairs on the head can grow for about 8 years if uncut; hairs on eyebrows grow about 4.2mm per month but will fall out every few months
Catagen phase: hair recedes from the bulb up toward the surface (in other words, recedes from inside out)
Telogen phase: no new hair or proteins are added by stem cells; stem cell pinches off and recedes and dies, taking stem cells and melanocytes with it
Hair on the scalp can reenter the growth anagen phase in proper conditions
Hair growth aids
- Minoxidil, originally used for hypertension, can also slow hair loss by increasing blood flow to hair cells. Side effects include lowered blood pressure, increased prolactin, and lowered libido.
- Mechanical accelerators like heating, lighting, or massaging the scalp can improve blood flow, but won’t completely halt hair loss.
- Tadalafil and platelet-rich plasma injections can also slow hair loss, but there is limited clinical data.
- Microneedling can stimulate hair growth and is a good addition to hormone-based treatments, but the studies are not conclusive.
- Botox can relieve scalp tension, but its efficacy is not well-studied.
The biology and psychology of hair
- Stem cells give rise to hairs we have on our heads and the surface of our body – every hair we have is there because of a stem cell population that gives rise to that hair
- Hairs are made up of a bunch of little proteins called keratin
- People experience tremendous anxiety and even depression about hair loss
Chemicals that affect hair growth
- Insulin growth factor-1 (IGF1) is a strong accelerator of hair growth by extending the androgen phase for a longer period of time
- Cyclic AMP is also a stimulator of hair growth follicles, acting as a messenger between the surface of cells and transmitting deep within the cells – this also extends the androgen phase
- Things that shorten the androgen phase, extend the catagen phase or telogen phase
- Two breaks on growth: phosphodiesterase (PDE) and TGF-beta-2
- Androgen-related alopecia (pattern hair loss)is testosterone and testosterone-derivative-related hair loss which takes place in men and women
- A healthy woman has higher levels of testosterone than estrogen, but less testosterone than men
Parts of hair
Hair root is the portion below the skin; the shaft is the part that grows out above the skin
- At the base there’s a pocket (hair cave) below the root with a population of stem cells; melanin also lives here and gives hair color
- Next to every hair root below the skin is a sebaceous gland – sebum is the oil produced by these glands
- Sebum is a strong antibacterial and hydrates the hair
- The erector pili muscle lies below bulb and goes to surface of skin – this is what gives rise to goosebumps and makes hairs stand
- Capillaries go into the bulb region to support stem cells and melanocytes, delivering oxygen and nutrients
