Breakthrough brings hope for baldness cure

17 May 2007

Scientists have discovered that hair loss isn't as irreversible as they thought. Adult mammals can, in fact, grow new hair follicles in response to a wound. Could this be the first step towards a cure for baldness? Antenna untangles the evidence...

This research was published in the journal Nature on 17 May 2007.

Image: iStockphoto.com/Sean Locke

Humans are surprisingly hairy creatures - on average we each have 100,000 hairs on our head alone. But it doesn't stay that way for long. By the time we're 35, almost 40% of men and women show some degree of hair loss.

Until recently experts thought that hair loss in mammals, including humans, was permanent. But now a team of US scientists have shown that mice can grow new hair follicles in the middle of a healing wound - turning conventional wisdom on its head.

This new hair took around three months to grow. It's white because it lacks pigment, but otherwise it's normal.

Image: George Cotsarelis

'Generally it's thought that mammals evolved to "repair" wounds rather than regenerate lost skin,' explains lead researcher George Cotsarelis, from the University of Pennsylvania School of Medicine.

'Our research shows that mammals are actually capable of highly complex regeneration. It's a completely unexpected finding.'

George Cotsarelis, University of Pennsylvania School of Medicine.

Image: George Cotsarelis

When mice have a wound larger than around 0.5 cm in diameter, stem cells - shown in blue - move to its centre and form new hair follicles.

Image: George Cotsarelis

George and his team were studying how wounds heal in mice when they noticed what looked like new hair follicles forming two weeks into the healing process. To work out where the new hair follicles were coming from, George used mice in which certain types of stem cell were stained blue.

It turned out that stem cells from the epidermis - the top skin layer - were responsible. 'Surprisingly, the stem cells that usually form hair follicles aren't involved,' says George. 'This again shows that mammals have a greater ability to regenerate than we realised.'

Why has no-one spotted this before?

Over 50 years ago, scientists thought they saw signs that mammals - including humans - could regenerate hair follicles during wound healing. But they didn't have the technology to prove it, so their work was largely forgotten. Now George has shown they were right.

The new hair follicles grow in a similar way to how they form in the human embryo.

Image: George Cotsarelis

George and his team also found that they could double the number of new hair follicles that grew by increasing the levels of a protein called Wnt. And he's confident that his research could have real potential for treating hair loss in humans.

'Instead of making a wound in the scalp, we could use dermabrasion (taking off the top few layers of skin as in some acne treatments) in combination with a compound that boosts levels of Wnt. This could lead to new ways to treat baldness.'

Most baldness is inherited, characterised by a receding hairline and bald spot in men, and thinning hair in women.

Cheng-Ming Chuong, University of Southern California.

Image: Cheng-Ming Chuong

Other scientists are impressed with the new findings. 'This is very significant and surprising research,' says Cheng-Ming Chuong, an expert in hair growth from the University of Southern California. 'Although the study was carried out on mice, the concept should be fundamental to all mammals - including humans.'

And George isn't just limiting himself to regrowing human hair. His research also opens up possibilities for the regeneration of other tissues - even limbs.

'We already know that the genes involved in the growth of new hair follicles are similar to those involved in the growth of limbs. The idea that one day this kind of approach could enable humans to regrow limbs is certainly in the back of our minds.'

Animals like newts and salamanders can regenerate entire limbs and tails, but until now mammals were thought to have limited regenerative ability.

Image: Pete Pattavina