One of the most notable women's social trends was short or "bobbed" hair, worn both for comfort and as a statement of liberation and modernity (women had got the vote in the U.S. in 1920). Short hair on women was uncommon before the 1920s. When required, as in medical war service or certain jobs, women could pin or roll their hair up, but the long tresses were usually still there. The first celebrity to cut or "bob" her hair was the famous dancer Irene Castle in 1915. She did it first for sanitary reasons when she had to have her appendix removed, but later was persuaded to keep the short hair, which became renowned as the "Castle Bob" and started the bobbed craze. After the "Great War", the style became more common (especially after 1920) and was adopted by liberated "flappers" and film stars who ditched their corsets and even girdles, and sometimes bound their chests to get a flatter look, and also wore increasingly shorter skirts (knee length by 1926), and later sometimes even pants (more common in the 1930s). By the mid and late 1920s, even many older women were cutting their hair shorter and skirts shorter (think "Auntie Mame"). Modernism had triumphed. "Bobbie pins" were invented as a way for women to "cheat"--keep their long hair liked by their boyfriends or husbands, but pin it up when they wanted to look more up to date. Here is a good short film on flappers and "The Bob" from Youtube:
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