Wrinkles can be caused by aging, exposure to ultraviolet rays and repeated facial expressions. Repeated contraction of muscles forms wrinkles!
However most people show wrinkles and fine lines with facial movement and expressions such as lifting eyebrows. That's normal. When wrinkles show at rest, that means skin damage.
Anti-wrinkle injections (Botulinum toxin) can prevents the nerve from telling the muscle to contract, therefore reduce wrinkles caused by repeated contraction of muscles.
After two weeks, skin recovered form damage and wrinkles disappeared.
Botulinum toxin relaxes the forehead muscle (frontalis).
Crows feet are another common treatment area.