One of this season’s key hair trends is sexily dishevelled hair. Perfect for summer and for Hollywood's year-round climate, it's no surprise stars are ditching straightening irons and rocking tousled 'undone' hair on the red carpet too. These laid-back locks make polished make-up and glamorous gowns fresh. Sienna Miller shows how relaxed hair can soften a structured outfit, while Mary-Kate Olsen proves that beach waves look just as good at a party as they do by the sea. But there’s a fine line between unwashed, messy hair and a sexily, mussed-up do. Lou Page the Olsen twins’ stylist tells us how to stay on the right side. 'Add some gentle texture with Redken’s touch control texture whip, £9.95, and gently rough dry with fingers for shape. For a more defined tousle, use a tong on large sections.'