Recent breakthroughs in stem cell research and fat metabolism are transforming our understanding of what makes hair grow
To understand hair growth, we must first appreciate the sophisticated structure of the hair follicle—often described as a "mini-organ" for its complexity. The follicle consists of multiple layers: the outer root sheath, inner root sheath, and the hair shaft at the center 5 . Critical to the growth process is the dermal papilla, a structure of mesenchymal cells at the follicle base that controls the number of matrix cells and subsequently determines hair size . The bulge region, located where the arrector pili muscle attaches, serves as a reservoir for epithelial stem cells that play a vital role in regenerating the follicle during each growth cycle 5 .
Interactive diagram showing key components of a hair follicle
Hair growth occurs in a continuous cycle with four distinct phases:
This is the active production phase lasting 2-8 years for scalp hair . During anagen, matrix cells in the hair bulb rapidly divide, producing the hair shaft upward through the follicle. Approximately 85-90% of scalp hairs are in this phase at any given time 3 .
A brief 2-4 week transition period where hair growth stops, the lower portion of the follicle regresses, and the dermal papilla detaches from the follicle base 3 .
A 3-month period of follicular quiescence where the hair remains in the follicle but is no longer growing. Normally, about 10-15% of hairs are in this phase 3 .
The final stage where the old hair shaft is released and falls out, making way for new hair growth .
The balance between these phases determines our hair density and length. In healthy individuals, the anagen-to-telogen ratio is approximately 12:1 to 14:1 . When this ratio shifts—due to factors like genetics, stress, or inflammation—hair thinning and loss can occur.
For decades, scientists believed that hair growth originated from stem cells in the bulge near the follicle base. However, groundbreaking research from the University of Virginia published in 2025 has upended this long-held belief 8 . Dr. Lu Q. Le and his team discovered a previously under-appreciated population of stem cells in the upper and middle sections of the hair follicle that serve as the earliest ancestors of our hair.
"These findings add new foundational knowledge to hair follicle biology, showing, for the first time, that the bulge cells actually arise from this novel stem cell population,"
Even more promising, the researchers found that in human bald scalp, although hair shafts are gone, these novel stem cells remain present. This means if we can reactivate these cells to migrate down and repopulate the bulge, we could potentially regrow hair in bald scalp 8 .
Meanwhile, researchers at UCLA have uncovered how cellular metabolism controls hair growth 9 . They found that hair follicle stem cells have different metabolic states when active versus dormant. Specifically, active cells have higher levels of lactate, a key energy-producing molecule 9 .
The team developed a drug called PP405 that increases lactate levels in dormant hair-follicle stem cells, effectively "waking them up." After confirming the mechanism in mice, they've conducted safety trials and plan effectiveness trials for the coming year 9 . Unlike current treatments that only slow hair loss, PP405 aims to reactivate dormant follicles to spark new growth.
One of the most promising recent studies comes from National Taiwan University, where researchers developed a serum that stimulated complete hair regrowth in bald mice within approximately 20 days 1 4 . The research, published in the prestigious journal Cell Metabolism, was led by Professor Sung-Jan Lin and his team 1 .
The investigation began with an observation: when skin is injured, immune cells called macrophages trigger nearby fat cells to break down and release specific monounsaturated fatty acids (MUFAs), particularly oleic acid and palmitoleic acid 1 4 . The researchers hypothesized that these fatty acids might be signaling hair follicle stem cells to activate.
Noted fatty acid release during skin injury response
Confirmed specific MUFAs (oleic and palmitoleic acids)
Identified CD36 as the fatty acid transporter
Discovered PGC1-α activation by MUFAs
Developed and applied fatty acid serum
Documented hair regrowth in 20 days
The results were striking—within 20 days, the treated mice showed significant hair regrowth, while control groups remained largely bald 1 . The fatty acids had effectively mimicked the regenerative signal of injury without actual damage, activating dormant hair follicle stem cells through metabolic signaling.
| Parameter | Before Treatment | After 20 Days | Change |
|---|---|---|---|
| Hair Coverage | Minimal to no hair | Near-complete coverage | Dramatic improvement |
| Follicle Activation | Dormant stem cells | Activated stem cells | Successful awakening |
| Growth Timeline | No active growth | Visible regrowth in 20 days | Rapid response |
Regrowth
This discovery is particularly significant because it represents a novel biological pathway for hair regeneration. Current treatments like minoxidil and finasteride target blood flow or hormone regulation, not this newly identified metabolic signaling 1 . The NTU team has since filed a patent for their discovery and is exploring topical serum formulations for future human use 1 .
Studying hair growth requires sophisticated tools to measure changes that aren't always visible to the naked eye. Researchers employ several specialized methods:
The following essential materials are crucial for hair growth research:
| Reagent/Solution | Function | Example Use |
|---|---|---|
| Monounsaturated Fatty Acids | Activate hair follicle stem cells via metabolic signaling | Taiwanese serum study 1 |
| Lactate-Producing Compounds | Boost lactate levels to awaken dormant follicles | PP405 drug development 9 |
| CD36 Transporters | Facilitate fatty acid uptake into cells | Essential for MUFA absorption 1 |
| Minoxidil | Vasodilator that increases blood flow to follicles | Gold standard in current treatments 6 |
| Finasteride | 5-alpha-reductase inhibitor that reduces DHT | Addresses hormonal causes of hair loss 5 |
| Rosemary Oil | Natural alternative equivalent to 2.5% minoxidil | Plant-based treatment option 6 |
While the Taiwanese serum shows promise, the researchers caution that mouse studies don't automatically translate to human results 1 . Mice have much shorter hair cycles than humans, and what works on mouse skin under controlled lab conditions may not replicate on human scalps affected by pattern baldness 1 . Clinical trials with human participants, placebo controls, and safety monitoring are still needed.
The future of hair growth treatment appears to be moving toward personalized approaches based on individual biology. As Dr. Le noted, "It is our hope that these stem cells could one day provide a novel therapy for treating hair loss in people" 8 . Similarly, the UCLA team behind PP405 hopes their drug will be "useful for more people, and also for people suffering from different types of hair loss" like chemotherapy-induced hair loss 9 .
Mouse studies showing promising results with novel approaches
Human clinical trials for PP405 and fatty acid serums
Potential FDA approvals for next-generation treatments
Personalized hair regeneration therapies based on individual biology
Current progress in translating laboratory discoveries to clinical applications
The science of hair growth has evolved from superficial observation to profound cellular understanding. We've journeyed through the intricate dance of the hair cycle, explored groundbreaking discoveries in stem cell biology and metabolism, and examined a promising experiment that could revolutionize hair restoration. The once-simple act of "watching hair grow" has revealed itself to be one of the most sophisticated processes in human biology.
While more research is needed to translate these findings into safe, effective human treatments, the progress offers genuine hope. The day may come when rubbing a serum on your scalp or applying a metabolic activator can restore hair as naturally as it first grew. Until then, each new discovery brings us closer to solving the ancient puzzle of why hair stops growing—and how we might convince it to start again.
The next time you notice a new hair, remember: you're witnessing not just growth, but a cellular masterpiece years in the making.