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What makes hair curly?

Strand of curly hair

Research shows that the curvature of a hair strand depends on the nature of its follicle. When a follicle is asymmetrical, the hair that it produces is oval in shape and tends to curl. When it’s symmetrical, the strand that emerges grows round and straight.

A research team based in Clichy, France, used electron microscopy to compare curly and straight hair fibres. The former had a concave cross section with an uneven distribution of keratin (the primary component of hair) accumulated near its inside edge, beneath the curve. The latter were circular in cross section and symmetrical in structure with evenly distributed keratin, so that they grew straight.

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