We can blame, er, thank, Coco Chanel. I would post a link, but my post will get spammed, but there's an article on Slate from Oct. 25, 2012 that's interesting and discusses how skin lightening seems to be making a comeback in some cultures.
One of the earliest floating head ads I've seen! It's a drawing, not a cropped photo, but it still counts.
I sometimes wonder how it would've been like to live in the 20s.
The 1920's was the turning point in fashionable skin tone in the white upper classes. Up until then, freckles or tan implied that you worked outside, and did not have the leisure to avoid work. With the change to middle and lower class women working in offices, more travel available to southern climates, and more exposed skin....pale skin became the sign of working class, and the tan became the sign of the leisure class.