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I always knew UV radiation put us at risk of skin cancer, but it wasn’t until I got involved in dermatology research that I learned that most of skin aging is due to UV radiation, too. The statistics are alarming: 80-90% of the visual signs of skin aging are due to sun exposure (1, 2). According to the American Academy of Dermatology, the greatest (and most cost-effective) anti-aging intervention is sun protection (3). So how exactly does sun damage our skin?
How does skin know how to work?
Skin is remarkable in its ability to protect us from heat, dehydration, germs, and other harmful substances in our environment. In order to do its job, each skin cell obeys a control center - its DNA - that tells the cell what to do.
DNA carries genes, the recipes for creating many different “worker” molecules, such as proteins, that help skin to carry out its job. In young, healthy skin, the DNA control center sends recipes without a glitch, and the worker proteins are doing their jobs as programmed. The result is strong, hydrated skin, with even tone. It looks good and keeps you protected.
What happens when UV radiation gets involved?
UV radiation hurts both the DNA and the worker proteins. When UV radiation damages DNA, the recipes get messed up, creating proteins that don’t do their jobs correctly. It also damages existing proteins, rendering them unable to do their normal jobs.
The result? The common signs that we associate with aging - uneven skin tone, wrinkles, loose skin, visible blood vessels, and an overall leathery appearance (4). Furthermore, skin is impaired in doing its job of protection. If the DNA is sufficiently disrupted, this can even lead to crusty, scaly growths on the skin and more serious issues such as skin cancer.
What's the difference between UVA and UVB harm?
In a previous post, we explored the different parts of sunlight, including high energy UVB and UVA light. A general rule is that damage from UVB plays a major role in skin cancer, and a minor role in skin aging (5). In contrast, UVA-induced damage plays a major role in skin aging, and a minor role in cancer (5).
In terms of our skin health and aging, both contribute to disrupting our DNA command center and worker proteins.
UVB: poor chemistry with DNA
Let’s look a bit deeper into UVB. When sunlight shines on an object, the energy of its waves can either be absorbed or reflected. Light that’s reflected does little damage. Absorption is a different story.
Each molecule in our body has unique wavelengths of light that it can absorb. DNA happens to directly absorb UVB light. The negative consequence of this extra high energy is that UVB damages DNA, creating DNA errors called “dimers.” The best way to think about this type of damage is to imagine healthy DNA as a long, smooth wire. High energy from UVB light creates kinks in the wire, which then disrupts and causes errors in the DNA recipes.
Our skin cells do have repair proteins responsible for repairing DNA by removing the kink and making it smooth so the normal protein recipes are restored. However, UVB light can sometimes damage the cell’s repair proteins themselves, which means the DNA recipe is permanently damaged.
Proper worker proteins will never be produced by these cells. UVB light is most strongly associated with skin cancer because it is more likely to cause this permanent DNA damage. An uncontrolled, error-filled DNA program is what can lead to skin cancer.
UVA: the free radical factory
Next, what about UVA? UVA in not absorbed by DNA to a great extent but can be absorbed by many other molecules in the skin cell. Chemical reactions caused when UVA light is absorbed generate harmful compounds called “free radicals”. Free radicals react with DNA and proteins, breaking and reshaping both the DNA program and the proteins that keep your skin healthy and youthful.
This kind of damage is called “oxidative damage” and is what “antioxidants” help to protect against. Healthy skin uses antioxidants to repair this oxidative damage; however, just as UVB harms the proteins that fix DNA kinks, UVA can overwhelm the skin’s ability to repair the damage from free radicals.
How does this damage affect myappearance?
Over time, accumulation of UV damage to your skin’s DNA recipes and to molecules working to maintain healthy skin is what leads to skin cancer and photoaging. Many of the unhealthy skin characteristics mentioned above are closely linked to UV damage.
For example, sagging and leathery texture is caused by structural damage to skin proteins, uneven skin tone and sunspots are caused by damage to pigment-producing cells, and crusty, scaly growths come from damage to DNA’s control over cell growth (6).
It’s important to both block UVA and UVB high energy light and help skin cells conduct antioxidant repair of damage from what UV light will inevitably get through.
What do you think? Have you ever considered exactly how UV radiation harms our skin before? If you have more questions, leave them in the comments and I'll be glad to think it through together.
- Poljsak B, Dahmane R. Free radicals and extrinsic skin aging. Dermatol Res Pract. 2012. 135206
- World Health Organization, Sun Protection: A Primary Teaching Resource. 2003. https://www.aad.org/public/skin-hair-nails/anti-aging-skin-care/causes-of-aging-skin
- American Academy of Dermatology, Anti-Aging skin care: What causes our skin to age? https://www.aad.org/public/skin-hair-nails/anti-aging-skin-care/causes-of-aging-skin
- Han A, et al. Photoaging. Dermatol Clin. 2014; 32(3)291-9
- Skin Cancer Foundation. UVA& UVB, https://www.skincancer.org/prevention/uva-and-uvb
- Yaar M, Gilchrest BA. Photoaging: mechanism, prevention and therapy. Br J Dermatol. 2007; 157(5) 874-87