Leaving the house without brushing or styling your hair? That's the whole idea behind "depression hair," a "just-got-out-of-bed" hairstyle that's the opposite of neat blow-drys and other hair fancies.

It works on every hair type. Bobs for thin hair, however, have an even bigger advantage, says Izzy Warren, a top hairstylist at Hershesons London salon. Rather than make skinnier strands look wispy, ...