Sun damage occurs slowly from both UVA and UVB rays

June 1, 2005

Photoaging and damage to the skin from the sun's rays don't always occur through episodes of actual burning. In fact, quite often, the opposite is true. The damage is the result of small amounts of sun exposure continually over a long period of time.

Photoaging and damage to the skin from the sun's rays don't always occur through episodes of actual burning. In fact, quite often, the opposite is true. The damage is the result of small amounts of sun exposure continually over a long period of time.

That was part of the message Robert M. Lavker, Ph.D., shared at the 2004 U.S. Symposium of the International Society for Bioengineering and the Skin (ISBS). He also described the changes that actually occur in the various levels of the skin when photodamage occurs.

Heterogeneous collection Dr. Lavker, professor of dermatology and director of research in dermatology at the Feinberg School of Medicine at Northwestern University, says that photodamaged epidermis is a heterogeneous accumulation of basal cells as opposed to the relatively homogeneous nature of normal basal cells.

One interesting point, Dr. Lavker says, is that the uppermost living cells, such as the granular cell layer, appear normal in photodamaged skin. Another hallmark of photoaging is the stratum corneum, which thickens.

Below the epidermis, Dr. Lavker says the dermis will display dramatic changes.

"The area just beneath the epidermis is known as the grenz zone and in photodamaged skin it takes on a morphological appearance of a scar. New collagen forms and is organized in bundles that are horizontal to the surface of the skin and run parallel along the skin surface. This is an area of fibrosis and the exuberant collagen formation is a response to chronic inflammation," he tells Dermatology Times.

"The elastic fiber network becomes clumped and the fibers themselves lose their normal appearance. We also see a brisk inflammatory infiltrate and an increased number of degranulating mast cells."

Small doses Dr. Lavker and his associates recognize that most sun exposure occurs in small doses over the course of decades. They wanted to see if the skin actually experiences those anatomical changes from low doses of ultraviolet A(UVA) and ultraviolet B (UVB) radiation rather than just from high, intense, short-term exposure.

"They decided to experimentally expose human subjects to very small increments of UVB, as well as UVA radiation, and study the effects at the end of a five-week period of sub-erythemagenic doses of radiation. The study was done in the early 1990s and radiation was also administered through a good quality sunscreen with an SPF of 22.

"We found that UVA caused far more changes than UVB in terms of alterations, particularly in the dermis. They found alterations in the elastic fibers that were enhanced by the UVA, and they found a marked inflammatory infiltrate in the UVA irradiated sites, whereas the UVB irradiated sites didn't have any inflammatory infiltrate.

"That part is not surprising since the UVA is a deeper penetrating radiation and the UVB is mostly epidermal. However we also found that UVA rays also resulted in a marked thickening of the stratum corneum, which is similar to what one sees in photodamaged skin - much thicker than the UVB irradiation site."

Little protection The researchers also found that simple sunscreens provided very little protection from the stratum corneum thickening and some of the other dermal changes.

They found an unexpected increase in sunburn cells even with the UVA; unexpected because sunburn cells are an epidermal phenomena.

"We thought the UVA would be mostly dermal, but, the UVA can also cause epidermal damage.