Facial expression lines are caused by contracting muscles beneath the skin. BOTOX® works by physiologically weakening the muscles that are directly related to facial wrinkles. Sometimes referred to as cosmetic denervation, BOTOX® injection is the #1 safe and effective treatment for dramatically reducing wrinkles in the aging skin. BOTOX® is highly effective for crow's feet, frown lines, and worry lines. Results may be retained by repeating the procedure every 4 months.