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HOW COME?: Tangled hair

Which gets tangled more easily, curly or straight hair? What causes hair to tangle in the first place? asks a reader.

Ever had a hairbrush get stuck in your hair? Snarled strands can catch the bristles of a brush like Velcro grabbing Velcro. In fact, the scientific definition of tangles sounds tame by comparison: "groupings of hair that resist the draw of a comb."

If your hair "resists" on a regular basis, blame the cuticle, the hair's hard outer layer. Each strand wears a cover of overlapping cells that, under a microscope, looks like the rows of shingles on a roof. Run your fingers down a strand, from scalp to end, and the hair feels smooth. But rub against the grain, and the same hair will seem rough. That's because you've ruffled its "shingles."

It's these shingle cells that are responsible for tangling and matting. A sheltered hair, untouched by brushing, combing, high humidity, dry air or high heat, is a smooth, shiny cylinder. But real hair has spent months or years growing slowly out of its follicle in the scalp. Near the base, the newest section is covered in flat, neatly arrayed shingles. But farther along the strand, the shingles are scratched and worn.

Even farther from the scalp, the hair's shingles wear jagged edges. Some may have disappeared entirely, exposing the hair shaft underneath to even more damage. At their tips, hair strands may look as frayed as old ropes -- the dreaded "split ends."

But why do damaged cuticles mean tangling? Hair tangles, researchers say, when the ruffled and damaged shingles of one strand catch on the equally worn shingles of surrounding hairs. Hairs tangle into loose knots, and the knots may tighten down during combing or brushing. The more damaged the cuticle, the more friction between hair strands -- and the more tangle-prone the hair.

We might assume that curly hair tangles most, since hairs curve back on themselves and have more points of contact with their fellow (damaged) hairs. But a 2007 study revealed the truth: Surprisingly, straight hair is snarliest.

Biophysicist Jean-Baptiste Masson had hairdressers in France count the tangles in hundreds of clients' hair over three weeks. Curlyheads had an average of three tangles, while straight hair averaged more than five knots per head. The salon results matched Masson's mathematical model of hair tangling, which he explained in the August 2007 issue of the American Journal of Physics. According to Masson, straight hairs tend to slide against each other at a steeper angle than curly hairs. And hair "shingles" are most likely to hook together at greater angles of contact. The result: more annoying tangles.

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