Wrinkle File : What is meant by "Expression Lines"?

Wrinkles are the first visible sign of the aging of the skin.… Sometimes, they appear in the form of fine dryness lines, sometimes as expression lines..

Expression lines are produced by the repeated action muscles - which number around 50 - as they form various expressions. Following the contraction of these subcutaneous muscles, even young skin creases, but it has enough elasticity to bounce back and become smooth again. It's similar to what happens when you fold paper in the same spot over and over. With age, however, the loss of elasticity results in the inability of the skin to regain a perfectly smooth surface and, as a consequence, the marks formed by such contractions remain visible.

Expression lines or wrinkles are located in very specific areas of the face. Furthermore, they are always formed perpendicular to the direction the subcutaneous muscle contractions take.