Frown lines are lines between the eyebrows. We use the glabella muscle to frown at times of stress, anger, concentration and tiredness leading to dynamic lines.
Repeated use of this muscle results in the lines becoming semi-permanent even when no facial expression is occurring, known as static lines.
The frown is usually the first area in the face to gain static lines. This is a common area to be treated resulting in a more relaxed look.