Source: http://www.wired.com/2015/01/whats-up-wi...

This matters because of an effect called “mere-exposure.” Formulated in 1968 by a psychologist named Robert Zajonc, it basically says that people react more favorably to things they seen more often. Zajonc tested this with everything from shapes, to facial expressions, even nonsense words. Since we see ourselves most frequently in the mirror, this is our preferred self-image. According to the mere-exposure effect, when your slight facial asymmetries are left unflipped by the camera, you see an unappealing, alien version of yourself.