In the ad, below, the woman couldn't
explain the pain to her male boss,
shadowed in the door window, because
it concerned menstruation,
unmentionable even today.
Note that the ad doesn't mention
coffee, which it would in America, and
not tea.
"My zone" is a woman's private zone
and off limits to her boss, and most
men, when it concerns menstruation
pain, including PMS. An American
douche liquid seems to have also used
the same concept decades earlier (Zonite).