The eyebrow muscles are used to express worry, anger, displeasure, discomfort, discontent, and other negative emotions. If these “extremeness” or "negative emotions" last for long then it can cause lines between eye brows. These lines are known as “frown lines” or “11 lines” but many people don’t have it and many have them. Frown lines can age you considerably. This is definitely something people don’t want to have.