Bald men will be pleased to know that scientists have found a way of making hair regrow.
They may be less delighted, however, to hear that it involves tearing their remaining hair out.
In a series of intriguing experiments, US researchers have shown that when they pluck 200 hairs, up to six times as many grow back.
For a thatch thickening trick to work, all of the hairs must be taken from one small patch.
It is thought that if enough hairs are forcibly removed from one area, it triggers a distress signal, and extra hair is grown to compensate.
While the concept may seem painful and peculiar, the University of Southern California researchers say it leads to potential new treatments for hair loss.
Millions of men around the world have male pattern baldness, with some starting to lose their hair in their teens.
Millions of women suffer also have thinning hair and experts say they may be more deeply affected by it psychologically.
Working with mice, the researchers marked out patches of fur of various sizes and plucked 200 hairs from each.
A month later, they looked to see how much hair, if any, had grown back.
When the plucked area was small, and so the hairs that were pulled out where tightly packed together, at least twice as many hairs grew back.
One lucky mouse sported new 1,300 hairs, including some outside the plucked patch, the journal Cell reports.
Further experiments suggested that plucking triggers a chemical distress signal that tells surrounding skin cells to start growing hair.
Even those that were ‘resting’ are jolted into action.
However, any men thinking of experimenting on themselves should note that the hairs were plucked one by one.
And results are far from guaranteed.
It seems that the chemical signal needs to be just the right strength for the trick to work.
If the hairs are taken from too big an area, the signal is weakened and no hairs grow back.
And if the plucked patch is too small, the missing hair is replaced but no extra hairs grow.
For mice at least, the best results are obtained by taking 200 hairs from a patch half a centimetre across.