Curly and straight hair - what's the difference between the two?

If you've ever wondered why some people have wild curls atop their heads and others have dead straight hair tonight we have the answer.

Kiwi scientists have made a breakthrough discovery that could lead to major developments in the $85 billion hair care industry.

Every week Jo Gullam spends an hour at the hairdressers having her curly locks straightened.

"It just takes so long to look after," she says. 

But the discovery of what makes hair like Ms Gullam's so wild could change everything.

AgResearch Senior Scientist Duane Harland says "It's been a mystery for quite a long time, about 50 years".

Using the study of Merino wool, Kiwi and Japanese scientists have found curls are caused by the length of cells surrounding the strand of hair.

When one side is longer than the other it pushes the hair over into the shape of an arch.

"And if you mix those cells around so that they're scattered everywhere, and they're not longer on one side than the other but they're scattered, then you get straight hair," Mr Harland says.

The findings could be revolutionary for the Merino wool industry - the curlier the hair, the better the insulation, warmth and filtration.

AgResearch Textiles Team Leader Dr Stewart Collie says "The structure of the fibre, the cells, the shape of the fibre all carries through to the product properties so when you make a garment or a floor covering".

The global hair care market worth a whopping 85 billion dollars is also set to benefit so for clients like Ms Gullam that could save not only money but also time.

"So I don't look like literally like a sheep," she says.