At the turn of the century, women still weren't comfortable wearing obvious signs of makeup. However, once WWI broke out, things began to change. Red Cross nurse volunteers were threatened with expulsion if they were caught with rouge — but on the flip side, it was also mandatory to look pretty in order to boost soldiers' morale.
The workaround this no-makeup rule was to use face cream to brighten your complexion. Helena Rubinstein famously ran ads that targeted women's duty to beauty during the war, writing, "Does your reflection give you quite the same satisfaction it gave you in 1914?" asked her 1916 advertisement. "Perhaps time and trouble have ploughed lines, where before, the skin was smooth and taut; or the complexion is dull and unattractive?"
She brought the message home, saying, "Even if your social or professional life does not demand it, your patriotism demands that you keep your face bright and attractive so that you radiate optimism."