Another cause and effect of beauty might have to do with why a particular group thinks something is beautiful. Most humans (and other animals as well) find symmetry beautiful. Symmetry was once a desirable trait because it would offer better genes to the offspring and increase their chance for survival. We no longer think of it in these terms, but most humans do still find symmetry beautiful. Another example might be more cultural and less scientific in nature. Each society develops its own ideas of beauty. The culture influences the young people in that group and they will find a particular trait beautiful. The simple cause and effect of society on its citizens can change the way we think of beauty in our contemporary society.
Another aspect of beauty is the tremendous influence it has in the lives of the public. Contemporary American society worships beauty, for beauty is equated with goodness, youth, vitality, superiority. Charles Dickens writes of the tremendous role in life that beauty plays. For instance, in his Great Expectations, Pip is dazzled by Estella, and he worships her in his youth as she is the "star" that he strives to attain throughout his life. The gentleman convict, Compeyson, receives a lighter sentence because he appears more handsome and civilized.
You could write about the use of airbrushing in magazine photography. The photos are sometimes so airbrushed that "reality" is gone. It is especially interesting to hear celebrities themselves criticize the amount of airbrushing that has been done on them. The use of air-brushing creates a false and unachievable example of "perfection" that sets up women (and men) to feel bad about themselves in comparison.
We can't write essays for you. But one cause and effect here is that women in the US, at least, can come to suffer from eating disorders because of the emphasis on thinness in our vision of what is beautiful. We put pressure on women to look thin and they sometimes end up harming themselves in an attempt to live up to those ideals.