The dermis lies between the epidermis and the subcutaneous fat. It is responsible for the thickness of the skin, and as a result plays a key role in the cosmetic appearance of the skin. The thickness of the dermis varies over different parts of the body and the size doubles between the ages of 3 and 7 years and again at puberty. With aging, this basic layer decreases in thickness and moisture. The dermis, which is laden with nerves, blood vessels, and sweat glands, consists mostly of collagen. The uppermost portion of this layer, which lies beneath the epidermis, is known as the papillary dermis and the lower portion is known as the reticular dermis. Smaller collagen bundles, greater cellularity, and a higher density in its vascular elements characterize the papillary dermis as compared to the reticular dermis. Fibroblasts are the primary cell type in the dermis. They produce collagen, elastin, other matrix proteins, and enzymes such as collagenase and stromelysin. These structural components will be discussed individually because each exhibits significant characteristics that influence the function of the skin. Immune cells such as mast cells, polymorphonuclear leukocytes, lymphocytes, and macrophages are also present in the dermis.
The junction between the epidermis and dermis is known as the dermal–epidermal junction (DEJ) (Fig. 2-1). Much is known about the attachment proteins found in the basement membrane of the DEJ. At this point there are no known cosmetic implications for this area, as such a discussion is beyond the scope of this book. Instead, this chapter will focus on the components of the dermis that are known to be important in aging.
Histopathology of the dermal-epidermal junction. The basement membrane separates the epidermis and the dermis. (Image courtesy of George Loannides, MD.)
Collagen, one of the strongest natural proteins and the most abundant one in humans as well as in skin, imparts durability and resilience to the skin. It has been the focus of much antiaging research and the target of several skin products and procedures. The importance of collagen is emphasized in the literature regarding many of the topical agents that are touted to increase collagen synthesis such as glycolic and ascorbic acids. Resurfacing techniques such as the CO2 laser and dermabrasion are intended to change collagen structure, thereby improving skin texture. Various forms of collagen are injected into the dermis to replace damaged collagen and to reverse the signs of aging. Finally, topical retinoids have been shown to reduce the collagen damage that occurs because of sun exposure. These sundry aspects of collagen health or replacement will be discussed separately in upcoming chapters; however, it is necessary first to gain an understanding of the structure and function of collagen.
“Collagen” is actually a complex family of ...