Women are socially conditioned from childhood to be concerned with their physical appearance. In addition to the much-publicized effects of being surrounded by relatively uniform, and very unrealistic, images of "beauty" in magazine, ads, movies, etc, women get praised or criticized by others for our looks. Comments like "You look so hot!" "Wow, your hair is gorgeous!" "You're looking so slim, have you lost weight?" feed into this as much as "Have you put on weight? You shouldn't eat that cookie, dear. Men don't like fat girls." and other negative comments do. This barrage of (often well-meaning) comments often comes from parents, partners, and friends, and therefore carries more emotional weight. Since people, and especially women, are biologically programmed to fit in, to want to be admired/appreciated/liked/loved, to please others, we are very vulnerable to all these messages. This audio soundtrack, combined with the constant visual reinforcement, and the emotional issues, make for some very heavy subconscious weapons pounding us with the ideas that there is one definition of beauty, that cellulite is disgustingly unsightly, that any tiny imperfections to face or form should be fixed immediately (and obsessed over in the meantime).
Once you are aware of where the pressure comes from, and all the components it has (including lessons from childhood about how your looks matter), it is easier to recognize it, and to try consciously to distance yourself from it. For better or worse, we are all judged - male and female - on initial impressions and appearance. But there is a difference in presenting a nice appearance - groomed, neatly and attractively dressed (which is fully and easily in your control) - and obsessing about those dimples on your thighs, the slope of your nose, whether your eyes are evenly spaced or the shape of your breasts (all of which you have very little control over).
When someone compliments you on your appearance, it is still a compliment and you don't need to slap them for it, but instead of feeling pressured to always look impossibly plastic-ly pretty, realize the compliment is saying, "I appreciate the respect you show for your self and others when you make an effort to be put-together."
Don't obsess over what you can't control, keep your focus on what is important - a healthy body and mind - and what you can do to achieve or maintain that.