HAIR FOLLICLES
Quorum sensing can direct collective regenerative behavior in a hair follicle population when an optimum number of hairs is plucked.Cheng-Ming Chuong

Initial results from a study suggest it may be possible to trigger hair growth by plucking a certain amount of hair, thanks to a collective decision-making process that is activated in hair follicles.

Where plucking a hair may result in it being merely replaced, a threshold density of hair when plucked can trigger almost a six-fold increase in hair in surrounding areas.

Researchers led by Cheng-Ming Chuong, a stem cell principal investigator at the University of Southern California, found the optimum response occurred when they plucked 200 hairs in circular patches of 3-5 millimetres in diameter in mice.

The plucking triggered 450 to 1300 nearby hairs to regenerate.

Each hair follicle undergoes seasons of growth, rest and fall. In people growing bald, the growing time is cut short and rest period prolonged till the stem cells that regenerate the hair totally stop producing new growth.

Plucking the optimum bunch pushes the follicle to start regrowing again. This happens due to a form of molecular communication, quorum sensing, that has been studied in bacteria and which triggers hair growth in a kind of injury response in skin, according to the study.

When only one hair is removed, the injury is treated as a minor one but when a bunch is plucked a coordinated response results in the lush regeneration. The accumulation of the inflammatory cytokine generated in sending the distress calls causes a widespread response, Chuong said.

This was tested by showing that regeneration did not happen in mice genetically engineered not to have some of these cytokines.

Whether the strategy will work in humans remains to be seen as hair growth in man and mice vary. Mice grow hair in waves allowing for closer coordination.

Baldness

It is also not clear if it will translate into a cure for baldness as the study did not use bald mice.

Many believe that baldness caused by an ageing stem cells population cannot be reversed by pulling shocks of hair.

However, the quorum sensing mechanism has generated interest in research circles for exploiting possible regenerative capacity in other organs.

Work on coaxing stem cells to regenerate hair has been ongoing elsewhere as also cures for the autoimmune disease alopecia areata where patients lose hair in patches.