VOA常速英语:How Heat Damages Human Hair

Many women and some men are very particular about their hair. One of the ways for keeping it in shape involves applying heat, but just how much of it and for how long has been mostly left to experience. A scientist from Purdue University, Indiana, is trying to find a scientific answer.

Some people who have naturally curly hair prefer to have it straightened.
 
Others with straight hair want to have curls.

“It is kind of like the way I see the world, like the lens through which I see the world and I always was wondering about how we can think about this from a mechanical engineering perspective," explains Tahira Reid, assistant professor of Mechanical Engineering at Purdue University.

Hair irons can take many shapes but are essentially clips or rods with heated surfaces.

“If you go to the mall right now you see an aisle full of straightening irons, and they have terms like ion technology and twirling," notes Amy Marconnet, also an Assistant Professor of Mechanical Engineering at Purdue University.

The heat weakens or breaks a protein called keratin, responsible for the hair’s shape, and temporarily changes it. But nobody knows exactly at what level the heat can actually cause permanent damage.

“If we understand the onset at which that happens than we might be able to intervene before or give some suggestions before you get to that point," Reid says.

Inside a Purdue University lab, a movable flat hair iron goes over a hair strand while an infrared microscope measures the changes in the hair’s structure.
 
Researchers say early results are a bit inconclusive. It turns out that everyone’s hair is different and that there's no exact temperature where hair straightening becomes hair damage. For example, people with naturally curly hair can suffer more damage from heat irons than those with straight hair.
 
Reid says they will continue their research in the hopes of finding that heat sweet spot for stylists.