Chronological Aging and the Causes of Wrinkles

Close-Up Of Woman's Eye

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Let's not kid ourselves; wrinkles are unavoidable. But while the reason we get wrinkles has to do largely with the inevitable—albeit unwanted—effects of aging, there are quite a few other factors you may never have considered.

To fully understand how we age and what causes the development of wrinkles, it helps to know the basic anatomy of our skin.

Skin Structure and Anatomy

Human skin is made up of several distinct layers:

  • The epidermis is the outermost layer of the skin and serves as a barrier to external elements. Within this layer new cells are constantly growing and pushing older cells closer to the surface, where they will eventually be shed. If this process becomes abnormal, the skin can appear scaly and flaky.
  • The second layer of skin is the dermis. It contains the structural elements of the skin, including key connective tissue. Different types of connective tissues serve different functions: Collagen gives skin its strength and plumpness, proteins known as glycosaminoglycans provide structural rigidity, and elastin facilitates flex and elasticity.
  • The dermal-epidermal junction lies in between the dermis and the epidermis. This structure forms fingerlike projections, called rete ridges, which increase the surface area of the epidermis exposed to blood vessels, allowing it to better absorb essential nutrients.
  • The bottom layer of skin is the subcutaneous tissue, which is largely made up of fat cells that insulate the body and make skin appear plumper and fuller. It also contains sebaceous glands, sweat glands, and hair follicles.

Wrinkles and other signs of aging are caused by changes to our skin. We can control, and even prevent, some of these. Others are beyond our control.

Chronological Aging

As a person ages, epidermal cells become thinner and less sticky, causing the skin to look noticeably thinner. The lack of stickiness hinders the skin's ability to function as a barrier, allowing moisture to be released instead of being retained in the skin. This causes dryness. Not only do epidermal cells decrease by 10% each decade, they divide more slowly as we age, making the skin less able to repair itself quickly.

The effects of aging on the dermal layer can also be significant. As this layer thins, less collagen is produced, and elastin fibers wear out. These cause the skin to wrinkle and sag. Meanwhile, sebaceous glands get larger as we age and produce less sebum, while the number of sweat glands decreases. The result is dry skin.

At the same time, the rete ridges of the dermal-epidermal junction begin to flatten out, making skin more fragile and conducive to shear wounds. This process also reduces the availability of nutrients to the epidermis, interfering with the skin's normal repair process.

Sun Damage

Exposure to the sun's UVA and UVB rays accounts for 90% of premature skin aging. The severity of skin damage by sunlight is also determined by an individual's total lifetime exposure to UV radiation in addition to their specific skin (pigment) type. Most photoaging effects, including wrinkles and dark spots, occur by age 20.

Excessive sun exposure affects the layers of the skin in different ways:

  • The epidermis becomes thinner, and skin lesions—including actinic keratosesbasal cell carcinoma, and squamous cell carcinoma—may begin to form.
  • In the dermis, excessive sun exposure damages collagen fibers faster than normal, and elastin fibers also begin to accumulate at abnormal levels. This accumulation causes enzymes called metalloproteinases to be produced in large quantities. Typically, metalloproteinases repair skin by producing collagen, but sun damage causes them to malfunction and actually break down collagen. This leads to the formation of collagen fibers known as solar scars. As the skin repeats this imperfect rebuilding process over and over again, wrinkles develop.

Free Radicals

Free radicals are unstable oxygen molecules that have only one electron—as opposed to the normal pair—and thus try to attach to other molecules in search of that second electron.

This process can alter the genetics of a cell. Free radicals cause wrinkles and skin damage by activating the metalloproteinases that break down collagen. The smallest amounts of UV radiation, smoking, or exposure to air pollution can worsen this damage.

Hormonal Changes

It is likely that the hormonal effects of menopause and decreased estrogen production contribute to the aging of the skin. While research has not, as of yet, determined which skin changes result from decreased estrogen levels and which are caused by excessive sun exposure or the normal aging process, studies in animals have found that a decline in estrogen decreases collagen levels by 2% a year and skin thickness by 1% each year.

Muscle Use

As it turns out, that old wives tale is true: Habitual facial expressions can cause the skin to wrinkle as it loses elasticity. Frown lines between the eyebrows and crow's feet radiating from the corners of the eyes develop as the tiny muscles in those areas permanently contract.


The effects of gravity can loosen the skin and create the appearance of sags due to the simple—and inevitable—gravitational pull. This can result in the jowls and drooping eyelids that are often present in older individuals.

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