Frown lines, horizontal forehead lines and crow's feet are not necessarily caused by the ageing process per se but are more likely the result of repetitive muscle movement.

As with any muscle group, frequent exercise results in a stronger muscle.  It is the same with the forehead, repeated movements such as frequent frowning, lying in the same position on a pillow, squinting, grimacing and smiling strengthen various facial muscles and over time cause visible, deep forehead lines.  

Botox relaxes these muscles leaving the forehead with a smooth clear appearance - and if performed properly, not frozen.