Skin aging: Genetic nuances

There are two distinct processes by which skin aging occurs-intrinsic and extrinsic aging, says Jennifer Linder, M.D., Linder Dermatology and Skin Cancer Center, Scottsdale, Ariz., and Assistant Clinical Professor of Dermatology at University of California, San Francisco.

Intrinsic factors are only responsible for only 10 percent of skin aging and based on DNA and gene expression. “Certain changes take place in the skin naturally due to the passage of time, but genetics also play a role in intrinsic aging,” says Dr. Linder.

While the Fitzpatrick Scale and the Global Heritage Model (which expands the definition of the Fitzpatrick Scale to include geographical ethnicity) can be used to identify the intrinsic factors of aging related to skin pigment, Dr. Linder points out, this is not the whole picture.

“These scales are all just pieces of the puzzle,” she says. “So many people alter their appearance with spray tans, hair color and even colored contacts, making a decision about how someone will react to treatment simply based on visual cues next to impossible. Asking the appropriate questions of a patient is the best way to gather the facts. Asking heredity questions are the best way to know genetic factors, but even that is highly individualized now, considering that many people have parents of differing hereditary backgrounds.”

Ethnicity affects the anatomy of the skin, including melanocytes, number of layers, and vascularity. “Genetically darker skin has more natural protection from the sun, yet their highly reactive melanocytes also make them prone to hyperpigmentation, either from UV exposure or other inflammatory stimuli,” says Dr. Linder.

The epidermis shows differences in the outermost layer, the stratum corneum, and its ability to function as a barrier. “One study demonstrated that the stratum corneum of African American skin contains 22 layers, while that of Caucasian skin has only 17,” she explains. “The thickness is similar, regardless of the number of layers, thus making the stratum corneum of dark skin more compact and prone to cohesion. This can lead to a reduction in penetration of anti-aging topicals, as well as a dry appearance with age. “

Transepidermal water loss (TEWL) tends to be greater in African American and Asian skin. This loss of excessive moisture leads to a reduced ability for the skin to protect itself against topical offenders, leaving it more susceptible to extrinsic factors. This impaired barrier function is thought to contribute to heightened sensitivity to topical stimulation, e.g. peels, that is more common in higher Fitzpatrick types, says Dr. Linder.  “There are significant differences in the dermis in skin of color as well,” she says. “It has been shown to be thicker and more compact than in patients with fair skin. The superficial blood vessels are more prominent and dilated, despite the vessels often being more apparent in fair skin. The thicker, more compact dermis allows for darker skin types to experience less visible wrinkling until a later age.”

She points out that everyone needs to practice UV avoidance and daily protection, regardless of ethnicity.

In men, skin should age slower because collagen production doesn’t slow until much later in life compared to women. However, UV exposure is a significant extrinsic factor in men, with many neglecting to use sun protection, particularly on the neck and ears. When testosterone production slows in the 30s and 40s, men do experience dryness and wrinkling says Dr. Linder. “The process of aging is the same, it just happens later in life in men,” she said. “The breakdown of the dermal structures would be the same, and based on a man’s or woman’s lifestyle choices and UV protection, or lack thereof.”