Expression lines form where the skin closely follows repetitive muscle movements, such as forehead lines, frown lines between the eyebrows, “crow’s feet” around the eyes and vertical lines on the upper lip.
Gravity-related wrinkles occur when collagen and elastic fibres are altered by ageing and can no longer counteract gravity: deep nasolabial folds and “marionette lines” accentuated by sagging of the corners of the mouth.
Sleep or positional wrinkles are related to habitual sleeping positions. At first they may disappear when posture changes, but over time they become permanent as elastic tissue and collagen are remodelled.
Sun-induced wrinkles (solar elastosis) are due to chronic UV damage in photo-exposed areas. The skin texture becomes more marked, multiple fine lines appear and the surface takes on a creased, “crumpled” look.