Intrinsic and Extrinsic Aging

A few people seem to maintain their young skin despite the years. Most of us, however, age visibly. There are two main forces that cause aging of the skin: intrinsic and extrinsic aging.

Aging changes are inevitable, but the rate at which they occur depends on intrinsic (internal) factors, such as genetic predisposition and hormonal surges, and on extrinsic (external) factors, primarily solar radiation. Thus, we call the natural process of change over time intrinsic (or chronological) aging. In contrast, we call the aging that results from damage that we inflict on ourselves extrinsic aging. The most common means of extrinsic damage is excessive exposure to the sun. The damage caused by UV radiation is called photoaging. The degree of photoaging that skin experiences is affected by the amount of exposure to solar radiation over an entire lifetime, and by the amount of protective melanin pigment in the skin.

Intrinsic aging eventually results in thinner, less resilient skin. The rate at which we shed cells from the surface of the upper layer, or epidermis (see A Brief Tour of the Skin) slows, causing the skin to look more opaque and to become less efficient at retaining moisture. Epidermal cells also are produced more slowly, so the skin thins. Expression lines progress to deep creases. The thick central layer, the dermis, atrophies, flattening and thinning. Vascularization — the number of blood vessels — decreases, resulting in slower repair and a decrease in pink coloring in fair skin. The numbers of hair follicles and sweat glands decrease, and the hair turns gray or white. Collagen and elastin show volume decline, but they remain structurally sound. Most women undergo a marked acceleration of these changes at menopause, when falling hormonal levels lower the rate at which collagen is replaced. Production of substances that hold water and thus plump the skin, such as hyaluronic acid, also decreases. In addition, a fall in sebum secretion interferes with the moisture barrier and protection hitherto afforded by a thin layer of natural oil on the surface of the skin. Skin becomes more subject to irritation because it is more fragile and less well protected.

Extrinsic aging speeds up most of these changes, but also causes other detrimental alterations in the structure and composition of the skin. Photodamage is most visible in older people, but the harm is often done when the person is a child or teenager. In addition to breaking down faster, collagen fibers are damaged, and elastin accumulates. In response, enzymes that normally increase collagen formation increase, but they may disrupt rather than fix the structure of collagen, causing solar scars. Over time, wrinkles develop. Skin may be rough and leathery, and have a yellow cast; it may be thin and tear easily. The walls of the blood vessels thin, resulting in easy bruising. Free radicals — oxygen molecules with only one electron, which steal electrons from other molecules — increase, in turn activating substances that break down collagen further. DNA repair is disrupted. Cells that are severely damaged normally die and slough off; photodamage interrupts this “suicide” process, so the damaged cells continue to live; actinic keratoses (bumps of disrupted cells that may be precancerous) and basal- and squamous-cell carcinomas (skin cancer) may result. Melanoma, a fast-growing and often deadly skin cancer, probably is caused primarily by sun exposure. Freckles, brown spots, and liver spots develop when the cells that produce pigment, the melanocytes, are damaged. Warty bumps (seborrheic keratoses) and moles also may appear.

In summary, photoaging causes both visible changes that most women do not enjoy, and physiological changes that are unhealthy.

So, if you have been sunbathing happily until now, what can you do? First, start covering up, to avoid compounding the damage that you have already done (see UV Radiation and Sunscreens). Second, do yourself a big favor, and engage a professional consultant. Fortunately, there are effective treatments available for many aspects of photodamage, and new approaches are being developed. Call our office (408-866-4884) to make a TLC (Total Look Consultation) appointment to begin restoration of a luminous, even-toned, plump, healthy complexion.