The different types of wrinkles.

The wrinkles represent one of the most visible signs of skin aging. They correspond to structural changes in the skin, resulting in the appearance of folds and furrows of varying depth on its surface. These changes stem from a gradual transformation of the different layers of the skin, particularly the dermis. Indeed, with age, both the number and activity of fibroblasts, the cells responsible for synthesizing collagen and elastin fibers, which provide the skin’s suppleness and elasticity, progressively decrease. Moreover, in the epidermis, keratinocytes divide more slowly over time, leading to the gradual thinning of this protective layer. Thinner skin becomes mechanically more vulnerable and less able to withstand repetitive stress. This is further compounded by a reduction in adipose tissue, that is, the hypodermis, which normally helps support facial volume.

The wrinkles however, are not solely the consequence of intrinsic skin aging. Several mechanical and environmental factors contribute to their formation and intensification. Constant gravitational pull exerts a continuous force on skin tissues, promoting their gradual sagging. Repeated positional pressures, notably those applied to facial skin during the sleep, can also leave lasting marks on certain areas. Repeated facial movements, driven by muscle contractions during expressions, impose ongoing mechanical stresses on the skin. Finally, oxidative stress, caused in part by UV exposure, accelerates skin aging.

Different classifications of wrinkles have been proposed in the scientific literature, allowing for a better understanding of their origin, evolution, and characteristics.

Among the different methods for classifying facial wrinkles, the distinction between dynamic wrinkles and static wrinkles is one of the most commonly used in dermatology and aesthetic medicine. This classification is based on the role of muscle contraction in wrinkle formation and allows differentiation between those that appear during facial movements and those that remain visible at all times, even at rest.

Expression lines, also known as dynamic wrinkles.

Expression lines are generally the first to appear on the face. From around the age of 30, collagen and elastin production begins to decline gradually—by about 1% per year—reducing the skin’s ability to withstand mechanical stress. In this context, the repetitive movements involved in facial expressions play a key role in wrinkle formation. Every smile, frown, squint, or jaw clench induces a transient deformation of the skin. With continued strain, the skin progressively loses elasticity and eventually folds repeatedly in the same areas. Initially, these lines are only visible during expression and disappear when the face is at rest.

Based on their location, several types of expression wrinkles can be distinguished:

• Frontal wrinkles, which take the form of horizontal lines appearing when the eyebrows are raised.

• Glabellar wrinkle, also called the interbrow wrinkle or glabellar line, corresponding to vertical or horizontal grooves located between the eyebrows, associated with muscle contraction (frowning) in this area.

• Bunny lines, or witch’s lines, located on the lateral and upper edges of the nose, resulting from contraction of the levator muscles of the nasal wing and upper lip.

• Crow’s feet wrinkles, or periorbital wrinkles, located at the outer corner of the eyes. They are among the first visible wrinkles, notably due to the particular thinness of the skin of the eye contour, which is four to five times thinner than the rest of the face, and the high number of daily blinks.

Static wrinkles, or age-related wrinkles.

Static wrinkles typically appear later and are visible even when the face is at rest. They result primarily from the structural aging of the skin, marked by a progressive decrease in dermal support proteins. These wrinkles can manifest across the entire face as well as on other areas of the body. Among the most common static wrinkles are:

• Nasolabial folds, which extend from the alae of the nose to the corners of the mouth and often indicate a progressive sagging of the cheek.

• Solar pleat wrinkles, also known as smoker’s lines or barcode wrinkles, situated vertically above the upper lip.

• Marionette lines, or labiomental grooves, which run from the corners of the mouth to the chin and impart a drooping appearance to the lower face.

• Neck and décolleté wrinkles, often horizontal, sometimes referred to as Venus rings, associated with the loss of subcutaneous adipose tissue and underlying bony changes.

Note : Some static wrinkles can also be influenced by sleeping habits. Sunlight is also a major factor accelerating static wrinkles, as UV rays produce free radicals that fragment and disorganize collagen and elastin fibers.

Beyond the distinction between dynamic and static wrinkles, some scientific classifications rely on the morphological appearance of wrinkles, which helps to better understand why certain wrinkles remain fine and superficial, while others become deep and permanently etched, regardless of facial movements.

Superficial atrophic wrinkles.

Superficial atrophic wrinkles correspond to fine, shallow lines, often multiple, giving the skin a crinkled appearance. They are mainly associated with a progressive thinning of the skin, both at the level of the epidermis and the superficial dermis. These wrinkles are frequently observed on areas where the skin is naturally thinner or more exposed to external aggressions. They can be exacerbated by a decrease in skin hydration and by an alteration of the natural moisturizing factors.

Deep elastotic wrinkles.

Deep elastosic wrinkles are characterized by pronounced, long-lasting folds, associated with significant changes in the extracellular matrix. They are closely linked to photoaging, that is, aging caused by chronic sun exposure. Unlike superficial wrinkles, deep elastosic wrinkles reflect lasting damage to the skin's supportive framework.

Gravitational folds.

Gravitational folds correspond to skin depressions linked to the progressive sagging of tissues, under the combined influence of gravity and diminished structural support. They do not result from simple muscle contraction but from a redistribution of facial volumes caused by reductions in collagen, elastin, and subcutaneous fat. These folds reflect an overall mechanical imbalance in which the skin and underlying tissues can no longer effectively counteract gravitational pull. They appear as broad, deep furrows.

This classification of wrinkles is primarily based on their appearance and structure.

The etiological classification of wrinkles is primarily concerned with their underlying cause, rather than their appearance or behavior during facial movements.

Wrinkles associated with skin atrophy.

Some wrinkles originate in a progressive atrophy of the skin, characterized by a reduction in the thickness and density of the skin tissues. This phenomenon is linked to a slowdown in cellular turnover, decreased fibroblast activity, and diminished extracellular matrix components. The skin thereby becomes more fragile, less resilient to stress, and more prone to visible lines. These wrinkles are part of the skin’s intrinsic aging process.

Dynamic and static expression wrinkles.

As mentioned previously, some wrinkles are related to the facial muscle activity. Dynamic expression lines initially appear from repeated facial muscle contractions, whereas static expression lines result from the gradual fixation of these folds over time. This progression reflects the skin’s decreasing ability to deform and then return to its original shape.

Wrinkles associated with skin laxity.

Wrinkles related to skin laxity are mainly caused by an alteration of the skin’s structural support. The reduction of collagen and elastin fibers, combined with the loss of subcutaneous fat, leads to progressive tissue sagging. The skin can no longer effectively counter mechanical forces, which fosters the development of pronounced folds and furrows.

Sleep wrinkles.

The sleep wrinkles represent a specific category linked to repeated mechanical forces applied to the skin during the night. Prolonged pressure of the face against the pillow, night after night, can imprint transient creases that, over time, become permanent. These wrinkles are often vertical, asymmetrical, and localized on the cheeks, neck, or décolleté.

The different classification systems discussed above can be combined with a more practical approach, involving the categorization of wrinkles according to their location on the face. This allows for an immediate assessment of the facial areas affected by wrinkles.

Facial wrinkles do not stem from a single mechanism, but arise from the complex interaction between intrinsic skin aging, mechanical stress, muscular activity, and environmental factors, which accounts for the existence of several complementary classifications.

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