Botulinum Toxin A injectables work best on dynamic wrinkles that occur in younger adults, before the wrinkle sets into the skin. Dynamic wrinkles occur when you make facial expressions and they are ‘quiet' when the face is not mimicking. With age and over time, these dynamic lines etch into the skin, and turn into a static wrinkle that is visible even when the face is at rest. Botox treatment weakens the muscle contraction which then lessens the overlying dynamic wrinkle.