Linearity and Surface Anatomy of the Face: From Embryo to Senescence.

Furrows, lines and wrinkles with distensibility and retractility are a biological need of skin in the service of skin integrity, plasticity and joint motion. The fundamental segmentation and linearity of skin is genetically coded, manifested early in embryonal life and remarkably constant throughout life. The basic pattern established early in embryonal life when facial segments expand and fuse is confounded by overlapping linearities of different backgrounds. Embryonal skin and skin in childhood, puberty, adult life and senescence undergo a general change in the direction of disturbed structure, nevertheless respecting the originally coded and segmented linearity. The fundamental linearity is expressed as the naso-frontal, maxillary and mandibular segments of the primitive face and the extremity buds forming extremities. The sensory nerves in this phase of morphogenesis follow and invade the segments of the face, trunk and extremities and form dermatomes,replicating the tissue segments. Early on, CREST cells migrate from behind, from the neural crest, and seed a normally hidden linearity in the tissues, which may appear as scleroderma lines, particularly the vertical "en coup de sabre" line(s) in the front. Later in pregnancy, during the phase of volume expansion, the resultant horizontal force applied to the outer skin results in gliding of epidermal structures relative to the underlying dermis, resulting in hair streams and whorls and bizarre V-shaped figures known as Blaschko's lines.Hairs in this process achieve their final distribution and inclination relative to the skin surface, known as Voigt's hairstreams and whorls. The dermatoglyphic lines and whorls of finger pulps share features with the two linearities explained by outer skin gliding. The fibre network of the dermis has uneven pretension, and circular wounds retract and become oval, systematically mapped as Langer's lines. Surgical incision lines influenced by static and dynamic forces to normal skin are described as Kraissl's linesand Borge's linesused to guide surgical incisions.Gravity acts as a constant vertical force on the face and entire body and results over years in gravitational lines, furrows and "hanging" skin. The sun creates its own pattern of disturbed linearity, photodamage lines and patterns that overrule the minute triangularlinearity, with accumulation of elastotic material in the dermis. Poor lifestyle and medical and psychiatric disease are associated with preterm skin ageing and increased furrowing. Skin linearity is complex with overlapping patterns. A broad insight into the essentials of skin linearity from the embryonal state to aged skin and senescence with an understanding and consideration of the ever-active influence of the genetic coding on skin linearities and ageing, including the forceful autoregulation aiming at the restauration of the natural state of the skin organ at any time and irrespective of interventions, is mandatory for professionals working on skin - plastic and aesthetic surgeons, dermatologists, cosmetologists, and cosmetic and decorative tattooists.
(© 2023 S. Karger AG, Basel.)