In 1920, when a young woman cut her leg shaving, it wasn't just an accident. It was national news, because shaving your legs was just that unusual:

How did women shaving their armpits and legs go from a freak story in 1920 to the mainstream by 1950?

The best research blames a sustained advertising campaign to change the way women groomed.

In the 1900s, most women didn't care about armpit or leg hair

As the 20th century began, women didn't care if they had leg or underarm hair, and it shows in the beauty guides, ads, and fashion of the time. Clothes were so concealing that it was rare to see bare legs or underarms, so removing hair there wasn't an issue. Before the 1910s, depilatories for those areas were used primarily by actresses or dancers, or for surgery.

Women did worry about hair other places. Christine Hope did the definitive research on women's hair removal in her 1982 paper "Caucasian Female Body Hair and American Culture," and her survey of ads in old Harper's Bazaar and McCall's magazines shows that they targeted facial, neck, and forearm hair. The legs and underarm were nowhere to be seen.

But new trends started to change everything within a few years.

Advertisers target the armpit

According to Hope, a shift began in 1915 when advertisers in Harper's Bazar started to target underarm hair (usually for various depilatory creams). A new trend in sleeveless dresses, often inspired by Greek and Roman clothing, exposed women's previously covered arms. That, of course, led the depilatory industry to conclude that underarm hair was undesirable.

This 1922 ad from Harper's Bazaar is typical of the genre that emerged:

This typical quote from a contemporaneous ad campaign says it all:

"The Woman of Fashion Says the underarm must be as smooth as the face"

The appeals were largely based on fashion, but they also told women what they should do to look fashionable (remove their underarm hair). Safety razors also got into the mix. As Gillette claimed in a typical 1917 ad: "Milady Decolette is the dainty little Gillette used by the well-groomed woman to keep the underarm white and smooth."

To some degree, the shift to increased shaving was made possible by technology, such as the the 1901 invention of a safety razor with disposable blades and the 1919 packaging of instant shaving cream. But that technology also needed to expand its market.

In the Roaring '20s, hemlines rise and the hair-removal industry targets legs

During the 1920s, knee-high skirts made legs more visible, and depilatory companies wasted no time claiming that their products enabled "a woman to bathe stockingless, without self-consciousness."

Hope's analysis shows that a relatively small percentage of ads focused on leg hair removal: in Harper's Bazar, for example, 66 percent of the ads mentioned it, but only 10 percent made it their sole focus.

Briefly, it even seemed like depilatories might just be a passing fad. From 1924 to 1926, ads for them disappeared from the Sears catalog and McCall's. And most of the ads were seasonal, running from around April to September — timing that suggests women mostly relegated hair removal to summer, when their underarms and legs were exposed.

That didn't last.

In the '50s, bare legs become the norm

By the 1940s, leg hair removal had become standard. By this point, all of the hair removal ads in Harper's Bazar mentioned leg hair, and 56 percent focused on the legs alone, according to Hope.

"We'd levy a demerit on every hairy leg on campus"

The more conservative McCall's didn't completely follow suit, but it also shifted toward leg hair, with salacious ad taglines like "Let's Look at Your Legs — Everyone Else Does."

And around this time, the media joined the ads in condemning leg hair. In 1939, Harper's Bazar wrote: "Ankle socks on the campus are a fine, old institution and all very well, but not on furry legs." There are hints that unshaved legs were still around at the time, but fading — in 1941, the magazine says, "If we were dean of women, we'd levy a demerit on every hairy leg on campus."

As the '50s ended, the transformation of American hair was complete. By 1964, 98 percent of American women ages 15 to 44 reported that they removed some body hair.

Did ads pressure women into removing their armpit and leg hair?

Can ads be blamed for the transformation? It's tough to know — a universal phenomenon like leg shaving that happens over decades is tough to pin down to a few ad campaigns. There was clearly a preexisting prejudice against body hair, too — that's shown by the ads in the 1900s that targeted face, neck, and arm hair. Changing fashion may have simply revealed a new area that needed to be groomed according to preexisting standards.

On the other hand, the advertising record hints that a lot of leg and underarm shaving was originally situational — women only shaved if they knew their underarms or legs would be exposed, and even then, it wasn't necessarily the norm yet.

In addition, as Hope notes, the instructional nature of many of the ads makes it seem like the ads were telling women what was appropriate instead of reenforcing existing trends. This ad from 1945 has to state exactly why a woman "needs" to shave her armpits.

One thing, however, we can know with certainty: in 1920 it was a story when a woman shaved her legs, and just a few decades later it was considered a story when she didn't.