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CHAPTER 32 Skin Integrity & Wound Healing
Epidermis The epidermis is the outer portion of the skin that functions as protection from the environment. The epidermis is made up of four layers, of which the most important are the inner and outer layers. ■ The stratum corneum, the outermost layer, is com- posed of numerous thicknesses of dead cells. Func- tioning as a barrier, it restricts water loss and prevents fluids, pathogens, and chemicals from entering the body. ■ The stratum germinativum, the innermost layer of the epidermis, continually produces new cells, pushing the older cells toward the skin surface. In the dermal layer, the keratinocytes are protein-containing cells that give the skin strength and elasticity. Deeper in the epidermis are melanocytes, which produce melanin, a pigment that gives skin its color and provides protection from ultraviolet light. Langerhans cells are mobile. Their function is to phagocytize (engulf) foreign material and trigger an immune response. Dermis The dermis lies below the epidermis and above the subcutaneous tissue. It is made of irregular fibrous connective tissue that provides strength and elasticity to the skin and is generously supplied with blood vessels. Within the dermis are sweat glands, seba- ceous (oil) glands, ceruminous (wax) glands, hair and nail follicles, sensory receptors, elastin, and collagen. This layer contains nerves that sense pain, touch, and temperature. Subcutaneous Tissue The subcutaneous layer is composed primarily of connective and adipose tissue. It provides insulation, conserves the body’s heat, pro- tects the inner organs, and reserves calories in the case of severe malnutrition. This layer varies in thickness in different body sites. Sex hormones, genetics, age, and nutrition also influence the distribution of subcutaneous tissue. Age-Related Variations Age affects the condition and structure of the skin. Infants and Children Infants are born with vary- ing amounts of vernix caseosa, a creamy substance that protects their skin. Their skin is thinner and more per- meable than that of adults, which predisposes infants to skin breakdown (e.g., diaper rash). Infant skin is at higher risk for fluid loss and greater systemic absorp- tion of topical agents applied to the skin, especially with prematurity (McNichol et al., 2021). The subcutaneous layer (brown fat) and sweat glands are not fully devel- oped, especially for preterm infants. As a result, in the first few weeks of life, thermoregulation is immature, and the infant must be swaddled to maintain body heat for the first days to weeks of life. Infant skin has other unique characteristics: ■ Milia —small, pearly white, firm, raised bumps on the face. They disappear after a few weeks.
■ Erythema toxicum —a common, harmless skin rash that occurs 1 to 3 days after birth and disappears by a week. It looks like small pustules (pimples) on a red base, often on the face, trunk, and arms. ■ Newborn acne —mild acne caused by the mother’s hormones passed to the baby. This rash most often clears in a few weeks. ■ Congenital nevi —birthmark that is darkly pigmented skin at birth, resembling a mole. They range in size, but larger nevi carry a greater risk of developing into a type of skin cancer. ■ Mongolian spots —blue-gray spots seen deep within the skin of the lower back and upper buttocks. They are most common on dark-skinned babies. ■ Café - au-lait spots —light-tan, flat marks on the skin that resemble the color of coffee with milk. They are often noted at birth but can also develop in the first few years of life. Café-au-lait markings indicate a con- dition called neurofibromatosis. ■ Port wine stains —flat, purplish markings on the skin caused by overgrowth of blood vessels under the skin. They are commonly seen on the face but can occur anywhere on the body. ■ Hemangiomas —raised overgrowth of capillaries (tiny blood vessels) that commonly appear in the first few months of life. ■ Stork bites —harmless flat red patches on the baby’s forehead, eyelids, and base of the neck. They are caused by stretching of the blood vessels under the skin. Adolescents and Adults Sex hormones released during puberty increase sebaceous and sweat gland activity, which leads to perspiration, odor, and some- times acne. In female individuals, especially during pregnancy, high estrogen levels may contribute to the softening of connective tissue and cause striae and dark- ening of the skin, usually on the face, areolae, nipples, vulva, and umbilicus, particularly in people with dark skin. Older Adults As adults age, the activity of the sebaceous and sweat glands diminishes, resulting in drier skin. Xerosis (itchy, red, dry, scaly, cracked, or fissured skin) is a problem for up to 85% of older adults and can be a threat to the integrity of their skin. With aging, especially in people with a lean body mass, the subcutaneous tissue layer thins. As the strong bond between the epidermal and dermal layer weakens, the dermal layer loses elasticity as a result of changes in its collagen fibers. These changes make the skin prone to breakdown and prolong wound-healing time. Regeneration of healthy skin and healing of wounds is significantly slower in older adults than in young adults. Furthermore, some older adults have chronic dis- eases that interfere with healing. Diabetes, for instance, predisposes a person to infection. Immune deficiency leads to slower wound healing, and liver dysfunction interferes with the synthesis of blood-clotting factors.
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