Because beauty is an ideal, an absolute, such as truth and goodness, the pursuit of it does not require justification. An ideal, by definition, can be met only by a minority of those who strive for it. If too many women are able to meet the beauty standards of a particular time and place, then those standards must change in order to maintain their extraordinary nature. The value of beauty standards depends on their being special and unusual and is one of the reasons why the ideal changes over time. When images of beauty change, female bodies are expected to change, too. Different aspects of the female body and varying images of each body part are modified to meet the constantly fluctuating ideal. The ideal is always that which is most difficult to achieve and most unnatural in a given time period. Because these ideals are nearly impossible to achieve, failure and disappointment are inevitable.
From the essay “Beauty is the Beast: The Psychological Effects of the Pursuit of the Perfect Body” – by Elaine Saltzberg (now Daniels) and Joan C. Chrisler
You can find the essay at this link: http://serendip.brynmawr.edu/sci_cult/courses/beauty/beast.doc (Word Doc)