Though zippers were introduced in the early 20th century, they did not catch on for women until later. By the 1930s, zippers were used more often sometimes for decoration, sometimes for function.
When women began to wear pants, side zippers provided a sleek look that was popular. Front zips were seen as too masculine.
It was when the ladies began to wear jeans that the front zip crept into women's wear. Mid-century teenaged girls would wear men's or boy's jeans with front closures. The trend became so popular that jeans for women started to feature front zippers. Though some brands had introduced front zips for women earlier, they did not catch on until the 1960s.