Results from the interaction of internal and external factors involving the skin.
Elastin and collagen loosen with age and comprise the intrinsic framework of the skin.
The interaction of muscles over the face when the intrinsic framework leads to the development of skin tension lines.
In general, skin tension lines are perpendicular to the underlying muscles of the face.
Aging extension of the appearance of such lines and is particularly associated with photoaging.
Skin tension lines vary between individuals, and some areas of the face have variability in the amount of change related to tension.
The forehead is subject to a muscle group that pulls it vertically, resulting in horizontal STLs in almost all patients.
Facial muscles of expression originated from insert into the skin, and are innervated by the seventh cranial nerve.
Synergistic and antagonistic groups of facial muscles enable the individual to vary their facial expression.
The frontalis muscle effects the forehead and eyebrow and creates horizontal wrinkles on the forehead, and assists with eyebrow elevations.
Corrugator and procerus muscles are antagonistic to the frontalis muscle of the forehead.
Orbicularis oculi muscles surrounding the eye and assist in closing the eye.
The nasalis muscle consisting of nasal and alar aspects, compresses and dilates the nares.
Mouth muscles are expensive and allow for significant facial expression,
The orbicularis oris surrounds the mouth and is the major component of the lips.
The orbicularis pearls pulls the lips against the teeth, draws the lips together and pulls the corner of the mouth to pucker.
Quadratus labii superioris muscle is a group of six muscles that controls the upper mouth:zygomaticus major muscle from the posterior lateral zygomatic bone and inserts in the upper portion of the orbicularis oris muscle and is primarily responsible in smiling, the zygomaticus minor muscle arising medial to the zygomaticus major and assists with its functions, the levator labii superioris muscle arises from the inferior part of the maxilla and inserts on the upper lip and helps elevate the medial part of the upper lip and assists the zygomatic muscles with open smiling, the levator anguli oris muscle inserts on the upper corner of the mouth and assists with lip elevation, the risorius muscle arises over the parotid gland and inserts into the lateral corner of the mouth and assists with smiling, the buccinator muscle arises posterior medial to the last molar tooth and becomes continuous with the orbicularus oris muscle and is the major component of the cheek muscles and prevents over the extension of the cheek and insists in whistling.