Why do we have curly or straight hair?

THAT'S THE WHY:Whether you cut it, style it to within an inch of its life, cover it or simply leave it be, your natural hair type falls somewhere on a spectrum between curly and straight.

Among Europeans and their descendants, about 45 per cent have straight hair, 40 per cent have waves and 15 per cent are curly-headed.

But what is it that determines whether hair naturally coils up in springy curls, hangs like a sleek curtain or lands somewhere in the middle?

Major contributors to the shape of your hair appear to include not only its makeup of proteins and how they bond together, but also how the hair grows out of the thousands of follicles in your scalp.

A study of hair growth published in 2007 found that people with curly hair have curved hair follicles, and that within each follicle there’s an asymmetric distribution of the cells that generate the hair, resulting in curlier output.

And last year, a group of researchers in Australia identified the trichohyalin gene as being a factor in determining hair shape in people of European descent.

The gene, which is expressed in the hair follicle, was already known to be involved in hair production, and it’s thought that variations in its make-up could influence the protein structure of hair and so contribute to curliness or lack of it.