1 Makes cheeks look thinner
The duck face makes cheeks look thinner and puts the emphasis on the cheekbones. This makes women look more attractive than they actually are.
2 Makes the lips fuller
Full lips make women more attractive to men because they signal good health and fertility. Some women make duck faces in an attempt to look more attractive in pictures.
3 Makes the eyes wider
Wide eyes are among the features that make women more attractive to men. When done correctly, a duck face can make the eyes look wider. (See Why Do Men Find Women With Big Eyes Attractive?)
4 Minimizes asymmetry
Studies have shown that symmetrical faces are found to be more attractive than asymmetrical ones, because the brain finds them easier to process. The duck face, when done correctly, can minimize the asymmetry of faces.
5 Mirror neurons
Mirror neurons are the set of neurons present in the brain that help us understand the feelings of others. When women see other women taking selfies with duck faces they feel like they want to do the same.
6 They noticed that their friends look more attractive
A woman doesn't have to know anything about beauty standards to notice that a picture made one of her friends look better. As some women notice their friends looking better after making duck faces, they start doing the same to also look better in pictures.
7 Attempting to blow a kiss
Some women do duck faces with the conscious goal of appearing like they are blowing a kiss. Those women do so to make their pictures seem more attractive.
8 Brings the face near to the ideal one
According to psychology, the ideal woman's face from an evolutionary perspective should have big eyes, full lips and narrow cheeks. The duck face helps women's faces become closer to the ideal face. (See Why do people take selfies?)