style police; The season's hair is tousled, slept-in - even filthy. Easy-peasy? Think again. Hester Lacey reports
Why, pray, is Jennifer Aniston looking so smug about that mane of smooth, glossy, thick hair? So dull, so predictable, so girl-next-door. She should be ratting it and teasing it up with backcombing - or getting it good and dirty. John Galliano started the ball rolling at his show for Givenchy in October last year; the models strode out with their hair in enormous mud-packs, sculpted into shapes that resembled "pasta soaked in cream sauce and rolled into profiterole-like piles", according to one bemused fashion magazine. The look was created by top French coiffeuse Odile Gilbert, who topped off her creations with trumpets and bells, all firmly rooted in the gunk. The models, it seemed, loved it. When your hair is teased, curled and sprayed several times a day, it is heaven (apparently) to have it slathered in dirt and left alone.

The towering, ratted birds' nests that many designers are currently favouring also have a certain sleazy feel. Marrying elegant catwalk fashions with a frothing bed-head is supposed to make the clothes look easier to wear. Big tousled hair (backcomb, think volume, ignore split ends) is also meant to be sexy, as if one had just tumbled out of bed. Never mind that most women are likely to wake up with flattened hair, not a bouffant that has miraculously appeared overnight (it will probably also be sticking out at an odd angle, often on one side only). Again, teasing up a huge mane is easier on hair that is not too smooth and slippery-clean.

Recreating these looks at home is not as easy as it may seem, however. This is because the couture version of "dirty" hair does not consist merely of not washing for a few weeks. This dirt is clean dirt; wash first, then create that filthy look with the help of gels and texturisers that mimic the look of natural grease perfectly (but smell nicer).

But binning the Silvikrin could actually do some good. Some trichologists claim that healthy hair and scalps depend more on brushing (the equivalent of those lengthy grooming sessions that our ancestors the apes indulge in) than on washing with pro-vitamin B formulas, added panthenol, extracts of natural Swiss mountain herbs etc etc etc. Really genuinely filthy hair, however, has yet to catch on in fashionable circles; it remains the territory of pop stars (Take That all confessed to being shampoo-free zones), students and anti-road protesters.