Frown lines, or glabellar lines, are vertical lines that appear between the eyebrows. They are caused by small muscles between your eyebrows and in your forehead, an area called the glabella. Frowning and squinting contract those muscles, and over time this repeated action can cause permanent wrinkles. For people who want to lessen the lines they already have or prevent lines from forming at all, the most common treatment is to inject the muscles with a botulinum toxin (i.e. Botox ® or Dysport ® are approved medications for the treatment of glabellar lines).
The following pictures show various stages of glabellar lines:
photos created by Canfield Scientific, Inc., 2014