International Cleavage Day

Rabbi Aha b. Raba (circa 5th century) and Nathan the Babylonian (circa 2nd century) measured the appropriate size of the cleavage as "of one hand-breadth between a woman's breasts". The breasts should have a natural shape, and they should not be touching. As a general rule, the amount of cleavage that should be visible is 1 or 2 inches — 3 inches at the most. When the breasts are pushed up into unnatural shapes and more than 3 inches are exposed, it's called Hard Cleavage.

Lingerie manufacturers controlled and constructed the mandatory bustline of the 1990s. In their heyday, Wonderbra sponsored a National Cleavage Day in South Africa every year, and the webcast of the Victoria's Secret show became one of Internet's biggest events. By 2001, the event was being aired on network television with 12 million viewers for the first broadcast. Other lingerie manufacturers like Frederick's of Hollywood and Agent Provocateur also joined the competition by that time, with the former introducing a design called Hollywood Extreme Cleavage Bra that helped give the impression of a spherical cleavage like augmented breasts that was popularized by stars like Pamela Anderson.

The main purpose of the observance according to Wonderbra managers is to let the women realize their dignity is something special they should be proud of.