3.4: Age Changes in the Epidermis
- Page ID
- 83975
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Keratin and Keratinocytes
Thickness The overall thickness of the epidermis changes little with advancing age, though the epidermis becomes slightly uneven in different parts of the body. Of greatest importance is the fact that the stratum corneum in protected areas, such as those usually covered by clothing, becomes only slightly thinner. Therefore, the keratin retains most of its ability to serve as a barrier against microbes and viruses, water, and abrasion. However, the slight thinning allows certain substances to penetrate the epidermis more easily. Therefore, the elderly should be careful about skin contact with chemicals and topically applied medications.
Structure Two other microscopic changes in the epidermis have been observed. One is the increase in variability of the size, shape, and internal structure of keratinocytes in the deeper regions. These irregularities may indicate initial abnormalities in cells that are precursors to skin cancer. Skin cancers are among the most common types of cancer in the elderly.
The second structural change is a decrease in the strength of attachment and an increase in the spacing between cells and between keratin materials. These changes may be an additional reason for the increased chemical permeability of the epidermis. The separation of the scaly bits of keratin, with their flattening and broadening, also contributes to the age‑related increase in the scaliness of the skin.
Replacement There is an age-related decrease in the secretion of some signaling substances by keratinocytes. The rate of new keratinocyte production also decreases. The amount of decline is different in different individuals, and the rate of decline becomes much faster after age 50. By age 75, the rate of cell production may drop to 50 percent of the rate in youth. These changes cause a decrease in the speed of wound healing, leading to an increase in the risk of infection.
Melanin and Melanocytes
Aging affects the melanocytes also. The somewhat uneven distribution found in youth becomes much more pronounced because while the total number of melanocytes decreases, certain areas of the skin develop clumps of melanocytes. These clumps form dark "age spots" or "liver spots" that are noticeable against the gradually fading coloration of the rest of the skin. By contrast, the number of dark moles decreases because of the overall reduction in melanocytes. Still, the result is that the elderly have a paler but increasingly mottled skin coloration.
The widespread reduction in the number of melanocytes due to their shorter lifespans and slower production, combined with a cessation of melanin production in increasing proportions of the remaining melanocytes, causes a decline in protection from excess light. Therefore, elderly people who are exposed to sunlight cannot develop as dark a tan as they did when they were younger. It also takes them longer to develop a tan. This places the elderly at much higher risk of suffering sunburn and skin cancer from exposure to sunlight.
Immune Function and Langerhans Cells
Langerhans cells decrease dramatically with aging. By the time of very old age, the number of these cells declines to less than half the number present in youth. The reduction is greatest in areas of the skin chronically exposed to sunlight. Because of declining numbers of Langerhans cells, one of the body's first lines of defense is largely crippled. This leaves the elderly with more inn cancers that would otherwise be eliminated by the immune system. It also decreases allergic reactions by the skin. This change may seem beneficial since such reactions can be uncomfortable, but allergic reactions serve as a warning sign that the body has come into contact with a harmful agent (e.g., noxious chemicals). Without this warning sign, steps to avoid or correct problems are not taken, and this may place a person in jeopardy from these agents.