The dermis is the middle layer of skin, a tough and flexible matrix of connective tissue situated between the epidermis and the hypodermis. Its thickness varies across the body; for example, it is about 0.6 millimeters on the eyelids but can be up to 3 millimeters on the back, palms, and soles. The dermis provides structural support and connects the outer layer of skin to the fatty tissue beneath.
The Two Layers of the Dermis
The dermis is composed of two sections: the papillary dermis and the reticular dermis. The papillary dermis is the upper, thinner layer. It features cone-like projections called dermal papillae that interlock with the epidermis, forming a strong bond between the two skin layers. This layer consists of loose connective tissue, fine collagen fibers, and elastic fibers.
Beneath the papillary region lies the reticular dermis, which is thicker and comprises the bulk of the dermal layer. It is made of dense, irregular connective tissue with thick bundles of collagen arranged in a net-like pattern. This layer houses many of the skin’s accessory structures.
Key Components of the Dermis
The dermis contains several specialized components. Collagen is a protein that makes up about 70% of the dermis’s weight and provides the skin with its strength and resilience. Another protein, elastin, gives the skin its ability to stretch and then return to its original shape. Although less abundant than collagen, elastin is fundamental for skin flexibility.
This layer is also rich with blood vessels that transport oxygen and nutrients to the epidermis and help regulate body temperature. When the body is warm, these vessels widen to release heat from the skin’s surface. Nerve endings allow for the sensations of touch, pressure, pain, and temperature changes, and their density varies, making areas like the fingertips extremely sensitive.
Additionally, the dermis anchors structures like hair follicles, which grow hair. Each follicle is connected to a sebaceous gland that secretes sebum, an oily substance that lubricates the skin and hair. Sweat glands are also rooted in the dermis, producing sweat that travels through ducts to the skin’s surface to cool the body.
The Dermis in Skin Aging and Repair
The dermis undergoes changes over time that visibly affect the skin’s appearance. With age, collagen production by cells called fibroblasts slows, causing the dermal layer to become thinner. The elastin fibers also degrade and lose their ability to recoil effectively. This reduction in both proteins leads to the formation of wrinkles and sagging skin.
The dermis is also central to healing following an injury that breaks through the epidermis. When the skin is wounded, fibroblasts in the dermis are activated to produce new collagen fibers to mend the damage. This newly formed collagen creates a dense, fibrous network that fills the wound, resulting in the formation of scar tissue.