UVA UVB
UVA, UVB and Skin Cancer
UV radiation is part of the electromagnetic light spectrum that reaches the earth from the sun. It has wavelengths shorter than visible light, making it invisible to the naked eye. These wavelengths are classified as UVA, UVB, or UVC, with UVA the longest of the three at 320-400 nanometers. UVA is further divided into two wave ranges, UVA I, which measures 340-400 nanometers and UVA II which extends from 320-400 nanometers. UVB ranges from 290 to 320 nm. With even shorter rays, most UVC is absorbed by the ozone layer and does not reach the earth, both UVA and UVB, however, penetrate the atmosphere and play an important role in conditions such as premature skin aging, eye damage, and skin cancers. They also suppress the immune system, reducing your ability to fight off these and other maladies.
By damaging the skin’s cellular DNA, excessive UV radiation produces genetic mutations that can lead to skin cancer. Both the U.S. Department of Health and Human Services and the World Health Organization have identified UV as a proven human carcinogen. UV radiation is considered the main cause of nonmelanoma skin cancer, including basal cell carcinoma and squamous cell carcinoma . These cancers strike more than a million and more than 250,000 Americans, respectively, each year. Many experts believe that, especially for fair-skinned people, UV radiation also frequently plays a key role in melanoma, the deadliest form of skin cancer, which kills more than 8,000 Americans each year.
UVA. Most of us are exposed to large amounts of UVA throughout our lifetime. UVA rays account for up to 95 percent of the UV radiation reaching the Earth’s surface. Although they are less intense than UVB, UVA rays are 30 to 50 times more prevalent. They are present with relatively equal intensity during all daylight hours throughout the year, and can penetrate clouds and glass.
UVA, which penetrates the skin more deeply than UVB, has long been known to play a major part in skin aging and wrinkling (photoaging), but until recently scientists believed it did not cause significant damage in areas of the epidermis where most skin cancers occur. UVA contributes to and may even initiate the development of skin cancers. UVA is the dominant tanning ray, and we now know that tanning, whether outdoors or in a salon, causes cumulative damage over time.
UVB, the chief cause of skin reddening and sunburn, tends to damage the skin’s more superficial epidermal layers. It plays a key role in the development of skin cancer and a contributory role in tanning and photoaging. Its intensity varies by season, location, and time of day. The most significant amount of UVB hits the U.S. between 10 AM and 4 PM from April to October. However, UVB rays can burn and damage your skin year-round, especially at high altitudes and on reflective surfaces such as snow or ice, which bounce back up to 80 percent of the rays so that they hit the skin twice. UVB rays do not significantly penetrate glass.