Plucking hair out can stimulate growth

A new treatment for hair loss may be on the horizon, after scientists have found that selectively plucking hair in very close proximity can stimulate some startlingly dense regrowth.
Researchers have demonstrated that by plucking 200 hairs in a specific pattern and density, they can induce up to 1,200 replacement hairs to grow in a mouse.
"It is a good example of how basic research can lead to a work with potential translational value," said Cheng-Ming Chuong, from the University of Southern California (USC).
"The work leads to potential new targets for treating alopecia, a form of hair loss," said Chuong.

The study began a couple of years ago when first author and visiting scholar Chih-Chiang Chen arrived at USC from National Yang-Ming University and Veterans General Hospital, Taiwan.
As a dermatologist, Chen knew that hair follicle injury affects its adjacent environment, and the Chuong lab had already established that this environment in turn can influence hair regeneration.

Based on this combined knowledge, they reasoned that they might be able to use the environment to activate more follicles.
To test this concept, Chen devised an elegant strategy to pluck 200 hair follicles, one by one, in different configurations on the back of a mouse.

When plucking the hairs in a low-density pattern from an area exceeding six millimetres in diameter, no hairs regenerated.
However, higher-density plucking from circular areas with diameters between three and five millimetres triggered the regeneration of between 450 and 1,300 hairs, including ones outside of the plucked region.
Working with Arthur D Lander from the University of California, Irvine, the team showed that this regenerative process relies on the principle of "quorum sensing," which defines how a system responds to stimuli that affect some, but not all members.
In this case, quorum sensing underlies how the hair follicle system responds to the plucking of some, but not all hairs.

Through molecular analyses, the team showed that these plucked follicles signal distress by releasing inflammatory proteins, which recruit immune cells to rush to the site of the injury.
These immune cells then secrete signalling molecules such as tumour necrosis factor alpha (TNF-a), which, at a certain concentration, communicate to both plucked and unplucked follicles that it's time to grow hair.
"The implication of the work is that parallel processes may also exist in the physiological or pathogenic processes of other organs, although they are not as easily observed as hair regeneration," said Chuong.