"When you wet your hair, intentionally or unintentionally, the water brings whatever product is already in there back to life," says celebrity stylist Alex Dizon, who has recently worked with Sienna Miller. "If you're initially using the right products, you can easily reshape your hair and work with the extra body the humidity coaxed out." Use your hands and scrunch or twist sections around your fingers to coax frizz into waves. When skies are especially threatening, Dizon suggests using an antihumectant (humidity- and moisture-resistant) product. If you have fine hair, try Kiehl's Climate-Proof spray for thicker hair, opt for a cocktail of leave-in conditioner and gel or an anti-frizz serum like John Frieda's.