Eczema-like irritation caused hair to grow back on shaved mice within 20 days (bottom row), compared to much less noticeable growth on mice shaved without this irritation (top row)
Tai et al. 2025
Skin irritation promotes hair growth in mice by stimulating their fat cells – and a serum could cause the same effects in humans, without causing discomfort.
Hair loss can sometimes be treated with medications or steroid injections, but more effective therapies are being developed, such as the use of stem cells or medications that wake up dormant hair follicles.
Sung-Jan Lin of National Taiwan University and colleagues became intrigued by the role of adipose tissue in hair growth several years ago during an experiment on mice. “We unexpectedly discovered that after skin irritation, the size of skin adipocytes [fat cells] shrinks rapidly before hair begins to grow back,” says Lin. “We hypothesized that adipocytes might release fatty acids via a process called lipolysis to fuel hair regrowth.”
To better understand the process, they repeated the experiment by taking a closer look at the cells involved. First, they caused eczema in shaved mice by applying an irritating compound to parts of their backs. In less than 10 days, the team observed that the hair follicles of the mice were in the active growth phase and that these areas showed visible hair growth. This did not occur on areas without eczema or on other mice that were shaved but were not designed to develop the skin condition.
The researchers noted that this appeared to be because immune cells called macrophages moved into the layer of fat beneath the mice’s skin, signaling the fat cells to release fatty acids taken up by the hair follicle stem cells. This then caused the cells to produce more mitochondria, which provide them with energy, resulting in hair growth. This is consistent with previous research that hair removal sends an immune signal to nearby hair follicles, prompting them to grow more.
Eczema is not usually linked to hair growth in men, but other forms of skin irritation, such as applying a cast to a broken limb, have been linked to excessive hair growth.
Next, Lin and his team wanted to know if the presence of fatty acids alone, without prior irritation, stimulated hair growth, so they created serums composed of different fatty acids dissolved in alcohol. These were applied to areas of the skin of shaved mice that showed no irritation, which were then compared to other areas to which the serum was not applied and to other shaved mice. “We found that only adipose-rich monounsaturated fatty acids, such as oleic and palmitoleic acids, are effective in promoting hair regeneration when applied topically to the skin,” says Lin.
He says the researchers, who patented the serum, also saw promising results when applying it to human hair follicles in the laboratory and now plan to test different doses of serum on people’s scalps.
Lin doesn’t anticipate the treatment will have serious side effects. “Oleic and palmitoleic acids are naturally occurring fatty acids. They are not only rich in our fatty tissues, but also in many plant oils, so they are safe to use,” he says. “I personally applied these fatty acids dissolved in alcohol to my thighs for three weeks and found that it promoted hair regrowth. »
“The bottom line is that this has not yet been validated on human skin and animal models can be very different, especially when it comes to follicular biology,” says Christos Tziotzios of King’s College London. Similar serums are also in development, including one, based on plant extracts, that stimulates hair growth within weeks.
Nonetheless, Tziotzios says the latest study improves our understanding of hair loss and growth. “We knew that adipocytes played a role in the genesis of hair follicles, but this is the first time I have seen them used for regeneration,” he explains. It may also explain why some people experience hair growth after microneedling, he says, which involves rolling thin needles over the scalp, making tiny pricks that trigger an immune response.
