Showing skin is always in fashion, but which body part gets the attention does change. "Each season has its own erogenous zone," designer Carmen Marc Valvo told Newsweek.

So which female body part has the starring role today? It's the back.

For spring and summer 2009 fashion, the sexy focus will be on the back with intricate, eye-popping dresses that show off a woman's back--from nape to tailbone, reports Newsweek, which made the observation based on a careful scrutiny of more than a dozen 2009 fashion presentations during Mercedes-Benz Fashion Week in New York.

The latest in dress fashion can be described like this, according to Newsweek writer Elisa Mala: "Business in the front, party in the back."

Showing skin has always been sexy, but different times like different body parts, according to Psychology Today. Playing peek-a-boo with erogenous zones is the most provocative force in fashion. While men's clothing spurns erogenous zones, women's clothing fully exploits them--from breasts to hips to derriere and then by extension the waist, shoulders, back, legs, ankles and midriff.

"When strategically surrounded by clothing, these areas function like traffic lights, stopping and starting points that direct the eye to a further destination--thus fulfilling what Freud regarded as a major component of the sex drive, 'the libido for looking,'" writes Linda Dyett in Psychology Today.

It works so well because of our tendency to fantasize. Sexy fashion works best by not revealing everything; instead, it leaves room for the imagination to work when just a portion of skin is revealed.

Which female erogenous zones were fashionable when?