Everyone knows the importance of sun protection, so I will not repeat it all over again. What some might not know is what exactly happens to your skin when you walk away from the beach with that beautiful suntan. Perhaps in the short term, it makes you look good, but that golden color is not all you're getting. What appears as “attractive tanned skin” is actually the result of injury to the skin. Essentially it is damage to DNA that causes the tanning response, in other words tanning doesn't begin until some damage has already happened1. This leads to the conclusion that there really is no “safe” suntan….
The major source of the damaging effects of sunlight comes from ultraviolet (UV) rays: UVB and UVA. They have different wavelengths which penetrate to different depths of the epidermis and dermis. Also, they have different biological consequences, such as cellular damage and mutation, including DNA degradation, suppression of the skin's immune system, etc. When UV rays strike the skin and are absorbed by molecules of DNA, proteins, lipids, and water. The absorption of UV rays is ultimately responsible for UV-induced damage. The molecular mechanism of photo aging is a complex process in which UV radiation leads to the damage of key structural proteins, lipids and DNA. Cumulative assault causes the cells to become dysfunctional, and eventually the skin loses the ability to repair itself. In the worst cases, these dysfunctional cells can become cancerous. Also, the resulting damage affects the numerous processes that impair normal activity of the skin cells, such as melanocytes (pigment producing cells), fibroblasts (cell that secretes the proteins that form collagen and elastic fibers), and endothelial cells (cells that line the interior surface of blood vessels). Ultimately, chronic sun exposure will result in thinner skin. The skin's natural ability to slough off dead layers slows down, which makes it feel and look rough, irregular pigmentation increases, and the blood vessels becomes dilated and more prominent, giving the skin a mottled, reddish appearance.
During a summer day, approximately 3.5% of the UV radiation reaching the earth’s surface is UVB, while approximately 96.5% is UVA. Because of its longer wave-length, UVA has an ability to penetrate deeply into the skin, substantially contributing to chronic sun damage.
An interesting study was published in “Clinical Intervention Aging” journal in 20102. The study demonstrated asymmetrical skin aging between window-exposed side of the face and the non-window-exposed side. Although, the effect of UV radiation is now well recognized, most people are not yet familiar with indirect sun exposure. While UVB radiation is absorbed almost entirely by ordinary glass, at least 50% of UVA passes through the glass. The subjects who participated in this study, spent a great part of their life with one side of their face being overexposed to the sun through a window over a long period of time due to their occupation. The results were evident: the clinical scores for wrinkles on the cheek, wrinkles under the eyes, crow’s feet number and laxity wrinkles, and skin roughness were significantly higher on the window-exposed side than on the non-window exposed side. The study provides not only strong evidence of damaging contribution of UVA to the aging process, but also the need for daily sun protection against indirect, non-deliberate UVA exposure indoors, as well as outside.
Recently I had my own “sun-damage discovery” when I had my photograph taken with VISIA® facial imaging system. It shows the skin damage beneath the surface of the skin that is not detectable by visual examination alone. Here it is to the right.
After seeing the subsurface of my own skin, which I considered to be in reasonably good shape, I became even more committed to my sunblock. Did I say earlier I won’t bother repeating the importance of sun protection… I lied.
1. Tanning beds, skin cancer, and vitamin D: an examination of the scientific evidence and public health implications”. Woo DK, Eide MJ; Dermatol Ther. 2010;23(1):61–71
2. Assessment of cumulative exposure to UVA through the study of asymmetrical facial skin aging. Mac-Mary S, Sainthillier JM, Jeudy A, Sladen C, Williams C, Bell M, Humbert P. Clinical Intervention Aging. 2010 Sep 23;5:277-84.