Love your skin.
The frown lines refer to the vertical lines that develop between the eyebrows. These are present because of the repetitive action of the corrugator and procerus muscles situated just above the eyebrows.
These lines can, if pronounced, give an angry appearance. One of the most common areas to be treated with botulinum toxin, it can take years off someones appearance.
Injections are placed in the corrugator and procerus muscles in a flattened 'v' shape in order to inactivate these muscles and produce the best results.