What are the specific characteristics of the skin around the eyes?

The skin around the eyes is the thinnest in the human body, with a total thickness of about 0.3 to 0.5 mm, compared to an average of 1 to 1.5 mm on the rest of the face. This thinness is primarily due to a thin and lightly keratinized stratum corneum, combined with a reduced dermal thickness. In the eye contour area, keratinocytes, the main cells of the epidermis, exhibit fragile intercellular cohesion. This is related to a sparse network of desmosomes. As a reminder, desmosomes are complex molecular structures organized around transmembrane glycoproteins that ensure the junction between keratinocytes.

The thinness of the skin around the eyes thus facilitates the absorption of cosmetic actives present in eye care products eye contour but also promotes the penetration of allergens and environmental pathogens. Moreover, this thinness makes the skin translucent and easily reveals the blood capillaries. This is one of the reasons why the area around the eyes is often prone to bluish dark circles.

The hydrolipidic film is a thin emulsion composed of sweat, sebum, and water, which plays a crucial role in skin protection. It forms a semi-occlusive barrier on the surface of the epidermis, limiting transepidermal water loss and preventing the entry of pathogenic microorganisms. However, around the eye contour, this film is almost non-existent, due to a very low density of sebaceous and sweat glands, respectively responsible for the synthesis of sebum and sweat. This deficiency in the hydrolipidic film deprives the eye contour of natural protection against mechanical and environmental aggressions, as well as its ability to maintain its hydration. Indeed, in the absence of this protective mantle, water evaporates more easily at this area, which promotes the early appearance of signs of aging.

An interesting characteristic of the skin around the eyes is its neutral pH, which is approximately 7. This differs from the rest of the skin, which has a pH that is more acidic, around 5.5. This can be attributed to the near absence of the hydrolipidic film on the surface of the skin around the eyes. Indeed, this emulsion is responsible for the skin's natural acidity. The acidic pH of the hydrolipidic film is a key factor in the homeostasis of the skin barrier, the integrity of the stratum corneum, and antimicrobial defense. Indeed, ceramides, essential constituents of the stratum corneum, are synthesized at an acidic pH by pH-dependent enzymes. Less protected, the eye contour area is also more prone to inflammations, such as eczema.

Collagen and elastin fibers, found in the dermis and synthesized by fibroblasts, play a key role in the mechanical resistance, flexibility, and elasticity of the skin. More specifically, collagen, the main structural component of the dermis, ensures the cohesion and firmness of the skin, while elastin gives it the ability to return to its shape after being stretched. However, the density of support fibers is lower in the eye contour area than in the rest of the body. This characteristic is partly responsible for the formation of bags in this area and makes the eye contour particularly vulnerable to gravity and aging.

The epidermis and dermis are not the only layers with unique characteristics: the hypodermis, the deepest layer of the skin, also has its own peculiarities. Composed mainly of adipocytes, the hypodermis serves to cushion shocks, act as an energy reserve, and maintain body temperature. However, around the eye contour, this layer is extremely thin, which significantly contributes to the fragility of this area. The thinness of the hypodermis also enhances the visibility of the contours around the eyes, such as the hollows that form with age and make the eyes appear more tired. Indeed, over time, the slight fatty layer tends to slide downwards and accumulate on the lower eyelid, a phenomenon that, combined with the low production of collagen and elastin in this area, promotes the formation of adipose bags.

The eye contour is characterized by a particularly dense vascularization, both blood and lymphatic. This concentration of vessels can be explained by the presence of numerous nearby organs that require a constant supply of oxygen and nutrients, such as the periocular muscles, the lacrimal glands, and the nerves and appendages of the eye. Coupled with a thin skin thickness, this dense vascularization contributes to the high visibility of blood vessels in this area through transparency and the appearance of bluish dark circles.

"The eyes are the mirror of the soul." Cicero (106-43 BC)

If our eyes are such a clear mirror of our expressions and feelings, it's partly because they are highly expressive. This area houses numerous muscles, 22 in total, which are constantly engaged, whether through eye movements, blinking, or various facial expressions. However, this repetitive strain on the eye contour causes mechanical stresses that accelerate the mechanical wear of skin tissues, particularly that of the dermal support fibers, which are already scarce. Over time, the skin loses its resistance to traction and increasingly struggles to return to its original state after being deformed: the expression lines, initially temporary, then become permanent.