the many opinions and reactions of other people are what influence fashion. they might be positive comments which would increase that fashion's popularity, or if they are negative then the fashion might not be as common or popular.
the social factors which affect fashion are a result of the popularity of one style or another. when one person sees a fashionthey like on another person, they might try to reapply the look on...
The short answer is, those who control popular media. The public perception is prescribed. In asking this question you are on the first steps to enlightenment. Maybe typing zeitgeist into google will...