Hair regrowth treatment may soon take a major leap forward, as researchers in a recent study have successfully grown complete, fully functional hair follicles outside of the living body, in a dish. This was made possible by the discovery of a previously unknown third cell type, the accessory mesenchymal cell population, which is essential for growing functional hair follicles. These specific supporting cells allow the follicle to grow deep into the skin, a process called downgrowth, to produce a proper hair shaft.
By adding the newly identified cell type to previously constructed early-stage hair follicle structures, the researchers were able to create organ germs—specialized cells located at the very bottom of follicle— composed of three types of adult stem cells.
Under carefully controlled lab conditions, these organ germs grew into fully functional hair follicles, and when transplanted on skin, they survived and went through the hair’s natural life cycle.
The findings are published in Biochemical and Biophysical Research Communications.
A cycle of death and regeneration
Most organs in our body are formed before birth, during the fetal stage. Hair, however, is different because it undergoes repeated cycles of growth, shedding, and regeneration throughout our lifetime.
Each hair growth cycle begins when epithelial cells (which form layers and surfaces) and mesenchymal cells (which form supportive tissues) interact with the skin to form a small thickened patch called a hair placode, marking the beginning of hair follicle formation.
As the follicle develops, its lower portion enters a phase of active growth. After a set period, this lower part naturally shrinks and breaks down. Then the hair regrowth phase begins, powered by special stem cells located just beneath a region called the hair bulge.
While our body executes this cycle flawlessly, turn after turn, unless hit by hormonal issues or illness that cause hair follicles to die, recreating this process artificially has been a major challenge for scientists. Producing truly natural, fully functional hair in laboratory settings has long been a challenge.
In an earlier study, the team developed a 3D organ germ method that regenerated functional hair follicles using lab-engineered seed cells made from epithelial stem cells and dermal papilla cells. When transplanted into a living body (in vivo), the follicles regenerated successfully, but when grown entirely in a lab (in vitro), they failed to achieve full function or complete hair cycling.
Identifying the supporter among cells
In this study, they set out to identify additional cells that support hair follicle growth. They began by collecting a broad population of cells from the back skin of adult mice, suspecting that the cells responsible for driving hair growth deep into the skin were hidden within this mix.
They discovered that while epithelial stem cells and dermal papilla cells could form a basic hair bulb, only cells derived from hairy skin could trigger downgrowth and produce a hair shaft in a lab dish. These turned out to be PDGFR?+/Sca1+/CD34high+ mesenchymal cells.
Using the organ germ method, the scientists assembled different cell types into a bioengineered hair follicle seed arranged in a precise order: papilla cells at the bottom, supporting cells in the middle, and stem cells on top. Within two weeks in culture, the follicle began to grow downward and eventually produced a visible hair shaft.
To test their ability to grow in a real biological system, they transplanted the follicles onto mice. They observed that the hair follicles fully integrated with the system, forming natural nerve and muscle connections. The follicles followed a natural hair cycle, falling out and regrowing repeatedly for over 68 days.
These findings bring us a step closer to regrowing hair using adult organ-inductive stem cells. The next challenge is translating this approach to human hair follicles. If successful and optimized, it could enable fully functional hair follicles for transplantation, offering a promising new treatment for hair loss and alopecia.
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Publication details
Koh-ei Toyoshima et al, Fully functional hair follicle organ regeneration using organ-inductive potential stem cells with an accessory mesenchymal cell population in an in vitro culture system, Biochemical and Biophysical Research Communications (2026). DOI: 10.1016/j.bbrc.2026.153459
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