When you describe something as facial, it has to do with the face. Your facial expression is the smile — or frown — that you happen to be wearing on your face.
Your facial features are made up of your eyes, nose, mouth, cheeks — everything that together comprises your whole face. When you use the word facial as a noun, it means a spa treatment that usually includes a deep cleaning and moisturizing of the face. You might decide to get a massage and a facial at the fancy resort hotel where you're spending a relaxing week. The Medieval Latin root is facialis, "of the face," from facies, "figure, appearance, or countenance."