Frequently Asked Questions on UV Radiation
Image by Retha Ferguson
Ultraviolet (UV) radiation is a form of electromagnetic radiation emitted by the sun. UV rays are classified into three primary types based on the measure of their wavelength.
UVA rays have the longest wavelength and are not absorbed by the earth’s ozone layer. Prolonged exposure to UVA rays can cause skin cells to age leading to long-term skin damage such as wrinkle formation (photoaging). More recent studies suggest that UVA rays can also play a role in skin cancer because just like UVB rays, they provoke damage to the cells’ DNA (Source: Bulletin de L'Académie Nationale de Médecine 2014).
UVB rays have a shorter wavelength and are mostly absorbed by the earth’s ozone layer. These rays can damage the outermost layers of skin and are primarily responsible for sunburns. Unlike UVA rays, they are largely blocked by windows and are more likely to be filtered by clouds. UVB rays are considered the primary risk factor for development of skin cancer (Soure: World Health Organization 2006).
UVC rays have the shortest wavelength and are completely filtered out by the earth’s ozone layer. As a result, these rays never reach the ground. The only way that you can be exposed to UVC radiation is from an artificial source like welding torches, special bacteria-killing light bulbs, and mercury lamps. Although they are not considered a risk factor for skin cancer, UVC rays can cause severe damage to human eyes and skin including burns.
“UVB rays are felt to be the primary driver of skin cancers derived from ultraviolet light exposure. UVA rays penetrate deeper into the skin where the collagen resides and are associated with the development of wrinkles secondary to collagen loss. However, both UVA and UVB exposure can lead to the development of skin cancer so it is important to use a broad-spectrum sunscreen that blocks both UVA and UVB.”
— Dr. Ryan Weight
Does Where I Live Affect the Amount of UV Radiation I Am Exposed to?
A number of environmental factors can affect how much UV you are exposed to. Some of these factors include:
Time of the year: UV rays are strongest in the spring and summer months. During these seasons, the sun is at a higher angle, which increases UV ray intensity. However, UV damage can still occur during fall and winter.
Time of the day: UV radiation is most intense around noon (between 10am and 4pm) when the sun is at its highest point in the sky.
Latitude: UV rays are strongest in areas surrounding the equator for two reasons. First, the angle of the sun at the equator allows rays to travel a shorter distance before they reach the ground. And second, the ozone layer in these areas is naturally thinner. Therefore, less UV rays are absorbed.
Altitude: UV rays are more powerful at higher elevations because they have to travel a shorter distance.
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Weather conditions: Clouds can prevent UVB rays from reaching the ground. However, UVA rays are rarely affected and can still reach the skin on cloudy days.
Are There Health Benefits to UV Exposure?
Exposure to UV radiation can have certain health benefits, most importantly the way we metabolize vitamin D, which plays an important role in bone and muscle health. However, the American Association of Dermatology (ADD) advises against sun exposure or tanning beds as a mechanism to improve vitamin D levels. Instead, follow a healthy diet that includes foods that are natural sources of vitamin D including fatty fish like salmon and tuna (Source: American Association of Dermatology).
In addition, UV radiation in the form of lasers and lamps (phototherapy) can be used to treat certain skin conditions such as psoriasis. Recent studies have suggested that UV rays generate nitric oxide (NO), which may reduce blood pressure and improve cardiovascular health (Source: Dermato Endocrinology 2012). However, it is important to remember that these positive effects do not eliminate the negative consequences of UV exposure.
How Can I Protect Myself?
You can still enjoy time outdoors by taking the right measures to protect yourself against UV radiation:
Apply broad-spectrum sunscreen: Sunscreen is an important part of your UV protection strategy, especially if it protects you from both UVA and UVB rays. Regular daily use of broad-spectrum SPF 30+ sunscreen can reduce your risk of developing squamous cell carcinoma (SCC) by about 40 percent, and lower your melanoma risk by 50 percent (Source: Skin Cancer Foundation).
Cover up: Clothes can provide some protection from UV exposure. Wear long sleeves, a wide-brimmed hat, and don’t forget to invest in sunglasses that offer UV protection. UPF rated clothing can be used as a sunscreen equivalent.
Stay in the shade: Limit your UV exposure by staying in the shade between 10am and 4pm, when UV rays are strongest.
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