Cross-link theory explains aging in terms of the accumulation of errors by cross-linking, or the stiffening of proteins in the cell. Proteins link with glucose and other sugars in the presence of oxygen and become stiff and thick (Marin-Garcia, 2008). Because collagens are the most plentiful proteins in the body, this is where the cross-linking is most easily seen. Skin that was once smooth, silky, firm, and soft becomes drier and less elastic with age. Collagen is also a key component of the lungs, the arteries, and the tendons, and similar changes can be seen there, such as in stiffened joints.

The oxidative stress theory, otherwise known as the free radical theory of aging, is among those most understood and accepted (Jang & Van Remmen, 2009). Free radicals are natural by-products of cellular activity and are always present to some extent. It is believed that cellular errors are the result of random damage from molecules in the cells called free radicals.

It is known that exposure to environmental pollutants increases the production of free radicals and increases the rate of damage. The best-known pollutants include smog and ozone, pesticides, and radiation (Abdollahi et al., 2004; Lodovici & Bigagli, 2011). Other environmental sources thought to cause increases in free radicals are gasoline, by-products from the plastic industry, and drying linseed oil paints. There is also new evidence that chronic exposure to racial discrimination increases evidence of oxidative stress. This may provide some explanation for a number of the disparities in incidence and prevalence of several diseases that are associated with free radicals, such as heart disease (Pashkow, 2011). In youth, naturally occurring vitamins, hormones, enzymes, and antioxidents neutralize the free radicals as needed (Valko et al., 2005). However, with aging, the damage caused by free radicals occurs faster than the cells can repair themselves, and cell death occurs (Hornsby, 2009; Marin-Garcia, 2008).

Closely tied to both programmed and free radical theory is the immunity theory of aging. It is based on changes in the integrated neuorendocrine and immune systems. In this case, the emphasis is on the programmed deaths of the immune cells from damage caused by the increase of free radicals as aging progresses (Effros et al., 2005; Marin-Garcia, 2008). The immune system in the human body is a complex network of cells, tissues, and organs that function separately and together to protect the body from substances from the outside, such as bacteria. It is highly dependent on the release of hormones. In the simplest terms, the specialized B lymphocytes (humoral) and the T lymphocytes (cellular) protect the body against invasion by infection or other matter that is considered foreign, such as tissue or organ transplants. The results of animal studies have demonstrated that the cells of the immune system become progressively more diversified with age and in a somewhat predictable fashion lose some of their ability to self-regulate. The T lymphocytes show more signs of “aging” than do the B lymphocytes. The reduced T cells are thought to be responsible for hastening the age-related changes caused by autoimmune reactions as the body battles itself; healthy cells are mistaken for foreign substances and are attacked.

It is important for the nurse to understand that the exact cause of aging is unknown; there is considerable variation in the aging process. Not only is there variation between persons but also between the systems of any one person. Aging is a wholly unique and individual experience.

Cell renewal time increases by up to one third after 50 years of age; 30 or more days may be necessary for new epithelial replacement (Gosain & DiPietro, 2004). This change significantly affects wound healing. In a younger adult, if the skin is injured (e.g., a cut or scrape), the surrounding tissue becomes red (erythematous) almost immediately. This inflammatory response is the first step in the natural healing process. In an older adult, this inflammation may not begin to occur for 48 to 72 hours. A laceration that becomes pink several days after the event may be misinterpreted by the nurse as having become “infected,” when in reality, the healing process has only just started. Evidence of true skin infection in older adults is no different than in younger adults, namely, increasing redness and purulent drainage.

The number of melanocytes in the epidermis decreases. Fewer melanocytes means a lightening of the overall skin tone, regardless of original skin color, and a decrease in the amount of protection from ultraviolet rays; the importance of sunscreen is thus significantly increased (see Chapter 12). However, in some body areas, melanin synthesis is increased. Pigment spots (freckles and nevi) enlarge and can become more numerous with increased exposure to natural and artificial light. Lentigines appear, commonly referred to as “age spots” or “liver spots.” They are frequently found on the backs of the hands and the wrists, and on the faces of light-skinned persons older than 50 years of age. Thick, brown, raised lesions with a “stuck on” appearance (seborrheic keratoses) are more common in men and are of no clinical significance but can become cosmetically disfiguring if severe.

Many of the visible signs of aging skin are reflections of changes in the dermis. The dermis loses about 20% of its thickness (Friedman, 2011). This thinness causes older skin to look more transparent and fragile. Dermal blood vessels are reduced, which accounts for resultant skin pallor and cooler skin temperature. Collagen synthesis decreases, causing the skin to “give” less under stress and tear more easily. Elastin fibers thicken and fragment, leading to loss of stretch and resilience and a “sagging” appearance. Loss of elasticity accentuates jowls and elongated ears and contributes to the formation of a “double” chin. Breasts that were full and firm begin to sag. As will be seen, the impact of the change in elastin has implications for a number of other systems as well.

Sebaceous (oil) glands also atrophy. Sebum, produced by the gland, protects the skin by preventing the evaporation of water from the epidermis; it possesses bactericidal properties and contains a precursor of vitamin D. When the skin is exposed to sunlight, vitamin D is produced and absorbed into the skin. Continuing to produce Vitamin D is especially important because of the high incidence of osteoporosis (see “Structure, Posture, and Body Composition” later in this chapter and Chapter 18). All people need some sunshine and probably vitamin D supplementation every day, especially those living in residential care facilities who have fewer opportunities to be outside.

Older adults are at significant risk for both hyperthermia and hypothermia. When caring for frail older adults, gerontological nurses can promote healthy aging by helping their patients avoid extremes of temperature, prevent drying, and prevent exposure to toxic products (see Chapter 13).

Men and women in all racial groups have less hair as they grow older. Hair on the head thins. Scalp hair loss is prominent in men, beginning as early as the twenties. The hair in the ears, the nose, and the eyebrows of older men increases and stiffens. Women have less pronounced scalp hair loss (Luggen, 2005). For some, the accustomed hair color remains, but for most, there is a gradual loss of pigmentation (melanin) and it becomes dryer and coarser. Older women develop chin and facial hair because of the decreased estrogen to testosterone ratio. Leg, axillary, and pubic hair lessens and in some instances disappears in postmenopausal women. The absence of leg hair can be misinterpreted as a sign of peripheral vascular disease in the older adult, whereas it is a normal change of aging.

The various races have distinctive hair characteristics, which should be kept in mind when caring for or assessing the person. Almost all Asians have sparse facial and body hair that is dark, silky, and most often straight. African Americans have slightly more head and body hair than Asians; however, the hair texture varies widely. It is always fragile, and it ranges from straight to spiraled, and thin to thick. Whites have the most head and body hair, with an intermediate texture and form ranging from straight to curly, fine to coarse, and thick to thin.

The nail becomes harder and thicker, and more brittle, dull, and opaque. It changes shape, becoming at times flat or concave instead of convex. Vertical ridges appear because of decreasing water, calcium, and lipid content. The blood supply, as well as the rate of nail growth, decreases. The half moon (lunule) of the fingernail may entirely disappear; the color of the nails may vary from yellow to gray, although with the widespread use of acrylics on the nails, long-term effects are not yet known. The development of a fungal infection of the nails (onychomycosis) is not the result of aging but is quite common. Fungus invades the space between the layers of the nails, leaving a thick and unsightly appearance. The slowness of growth and the reduced circulation in the older nail make it very difficult to treat.

For suggestions of nursing interventions that promote healthy skin during aging see Box 5-2.