To end the year 2025, I leave you with some good news. At least for those who have some hair left in various parts of their scalp.
In 2011, a famous study from the US found that balding people still have intact hair follicle stem cells. However, they have a defect in the conversion of these stem cells into active progenitor cells (which were markedly depleted in bald scalps per the study findings). Among the authors of this report were the world renowned hair loss researchers Dr. Luis Garza and Dr. George Cotsarelis.
But now a new study from India has found that partially bald areas of the scalp retain most of their progenitor cells. Perhaps this bodes well for upcoming new hair growth treatments (such as Breezula and PP405) kick-starting the hair growth cycle all over the scalp in those who are not severely bald.
Note that in rare instances, even those who are at Norwood 5-7 levels of baldness have regained long-lost hair. Hair loss and hair loss reversal are still not close to being fully understood.
Partially Bald Regions of the Scalp Retain Progenitor Cells
The above new November 2025 Indian study found that partially bald areas of the scalps of men suffering from androgenic alopecia (AGA) retain bulge hair follicle progenitor cells. The ten patients in the study were all male Indians.
The authors mention that previous studies (see next section) have mostly focused on fully bald areas. But the hair follicles in partially bald areas of AGA sufferers were not characterized till now when it comes to the status of stem cell and progenitor cell populations.
Key quote:
“Quantification of CD34+ and Sox9+ cells revealed that the number of progenitor cells is not significantly reduced in the partially bald area compared to the hair follicles of the occipital unaffected area.”
In the below first image from the study, you can see the green and blue streaks showing how progenitor cells (CD34 and Sox9) still exist in partially bald regions in the front of scalps. Almost to the same extent as in the occipital non-balding areas of the volunteers’ scalps.
In contrast, fully bald regions of the volunteers’ scalps show no remaining CD34 or Sox9 progenitor cells. Note the absence of any green or blue lines in the top left section of the below image.
Bald Scalps Retain Hair Follicle Stem Cells but Lose Progenitor Cells
The news is very significant, and we need to go back in time to learn why. As I mentioned at the beginning of the post, In 2011, a team of US researchers from University of Pennsylvania School of Medicine found that:
“Bald scalp in men with androgenetic alopecia retains hair follicle stem cells, but lacks CD200-rich and CD34-positive hair follicle progenitor cells.”
So AGA is not characterized by the loss of follicular stem cells as was thought by many scientists. Rather, it is a defect in the conversion of these stem cells into active progenitor cells, which in turn leads to hair follicle miniaturization. This news was huge at the time and I have mentioned these findings a number of times in the past.
Another study from Egypt in 2015 confirmed these findings by concluding that follicular stem cells are still present in both men and women suffering from pattern hair loss.
On a related note, a Chinese study from 2020 found that vascular endothelial growth factor (VEGF) can protect CD200-rich and CD34-positive hair follicle stem cells from androgen induced apoptosis.
For those who are interested, the below image from this 2020 study from Poland is instructive. It depicts the location of hair follicle bulge stem cells in relation to the dermal papilla (DP), sebaceous gland, sweat gland, epidermis, dermis and adipose layer of the skin.
Other Changes in the Scalps of Hair Loss Sufferers
Over the years, I have covered numerous studies that analyze various changes that happen to the scalps of people who are suffering from hair loss.
Perhaps the three biggest findings that I can recall are that:
- Balding scalps have fewer fat cells and become thinner and tighter as fibrosis sets in. Not surprisingly, the transplantation of adipose-derived stem cells into balding heads has seen significant interest over the past decade.
- The arrector pili muscles get slowly destroyed in balding scalps. Albeit a fraction of these muscles may continue to exist even in entirely bald regions of the scalp.
- The balding scalp shows increased Prostaglandin D2 (PGD2) levels and decreased Prostaglandin E2 (PGE2) levels.
And now we can add progenitor cell population changes to this list.