There are two types of facial wrinkles: dynamic and static.
Expression lines are present at all ages and typically seen with facial expression such as smiling, frowning or raising eyebrows. They are the origin of the so called dynamic wrinkles, caused by the temporary contraction of facial muscles, causing the overlying skin to crease. In certain cases, particularly in the upper part of the face, they are associated with negative emotions as they give an angry or a concerned appearance. Frown lines, crow feet lines, and forehead lines are best reduced with botulin toxin.
Static wrinkles are always visible, even when all the facial muscles are resting, but become more obvious with facial expressions. Static wrinkles tend to develop in skin that is thinned and stretched as a result of natural ageing processes, and are more pronounced in UV damaged skin.