Frown lines are typically caused by the combination of sun damage and aging, as The Patient's Guide points out at Wrinkles.com. Frequent movement of the muscles used in scowling causes folds in the skin that become more permanent as the skin loses its elasticity from age and sun damage, according to About.com. Frown lines can be exacerbated by squinting, either to bring something into focus or against bright light.
The more facial skin is exposed to the sun, the more damage the sun's ultraviolet rays do to the skin's collagen and elastin. As a result, according to The Patient's Guide, skin is less able to remain smooth and taut over time.
Because repeated muscle movement is one of the factors causing frown lines, muscle immobilizers such as Botox provide an effective treatment option to help eliminate frown lines temporarily. As HowStuffWorks points out, Botox is the top nonsurgical cosmetic procedure performed in the United States. It works by blocking nerve signals, which allows the contracted muscles to relax, decreasing or eliminating the frown lines. The wrinkle-minimizing effects of Botox tend to last three to four months.
Other cosmetic procedures that are performed to eliminate frown lines include a forehead lift or the use of absorbable injectable fillers, according to HowStuffWorks.