At first, it looked like a coincidence when models looking like Kate Moss in the 1990s walked New York's runways earlier this year, but soon it became clear that the messy, sometimes even 'grungy' look of the period is back with a bang. Now, the trend has got its red carpet approval, with more than one celebrity opting for 'undone' hair despite the big occasion.

Actresses Jessica Biel and Chloe Sevigny both perfected the imperfection with their messy updos and loose strands, models Sasha Pivovarova and Karolina Kurkova's looks could be described as 'bed hair,' and young actress and Burberry spokesmodel Emma Watson opted for casual waves.

Unfortunately, this doesn't mean that you just have to fall out of bed to achieve this look. 'Undone' hair is sometimes just as time-consuming to do as more glossy options, even if you want to look like you don't care.

There are a few YouTube tutorials on how to get it right: try Raelyni's for an undone side bun, heather123's for messy waves, or bubzbeauty's for an updo with loose strands. All you need for most tutorials is a headband and bobby pins, sometimes curlers or straightening irons, and products such as TIGI's Bed Head.

Other beauty trends at the Costume Gala were more on the classical side, ranging from Old Hollywood waves (Taylor Swift, Iman, Eva Longoria), to smoky eyes (Zoe Saldana, Nicole Richie) and red lips (Gwen Stefani and almost everyone else).