Characteristics of UV and sources
Ultraviolet (UV) radiation is the band of non-ionizing radiation that lies next to ionizing radiation in the electromagnetic spectrum. UV radiation is categorized as UVA (400–315 nm), UVB (315–280 nm) and UVC (280–100 nm). The sun is the major source of UV but all of the sun’s UVC and much of the UVB are absorbed by the earth’s atmosphere so that at the earth’s surface the highest proportion of UV is UVA (over 90%). However, exposure to UVB is biologically far more relevant than UVA.
UVB levels experienced at the earth’s surface vary inversely with latitude so they are highest at the equator and lowest at the poles. Depletion of ozone in the stratosphere by man-made chlorofluorocarbons has led to greater levels of UVB in some high-latitude regions. UVB levels vary by season and by day, being higher in summer than winter, and highest around midday. Cloud cover decreases terrestrial UV. Reflection of UVB by the atmosphere and by light-colored surfaces such as snow, dry sand and water, considerably increases solar UVB levels at the earth’s surface considerably.
Several sources of artificial UV are found in occupational and medical settings. These include mercury vapor lamps, arc-welding equipment, and commercial bactericidal UV lamps and dental polymerizing equipment. Sunbeds used for cosmetic tanning have become a more prevalent source of UV exposure in many countries in the last two decades.
UV effects on the body and health implications
In humans, exposure of the skin to UVB in small amounts is responsible for synthesis of Vitamin D, which is essential for bone health. However, exposure of skin cells to high levels of UV radiation has harmful health effects. In the short-term, intense exposure of pale skin to UVB causes inflammation or sunburn and local immunosuppression. Long-term UV exposure of the deeper skin over many years causes skin wrinkling and premature skin ageing, as well as causing skin cancers such as basal cell cancer, squamous cell cancer and malignant melanoma.
Melanin is the naturally occurring pigment in the outer skin that is responsible for skin color. This serves to filter UV radiation physiologically and to shield deeper skin cells from UV damage. People with dark skin who have naturally high amounts of pigment in their skin therefore rarely suffer harmful skin effects from UV exposure. In those with pale skin, UVB exposure stimulates pigment cells to produce extra melanin to tan the skin and help protect it temporarily. Light-skinned people tan to varying degrees after sun exposure and people such as albinos and persons with red hair, who cannot tan, are highly prone to the harmful effects of UV.
Exposure of the eyes to high levels of UV radiation is also harmful. Intense UV exposure can cause inflammation of the cornea (outer surface of the eye) and retinal damage (rear of the eye). Long-term exposure causes degenerative changes such as unwanted tissue growth on the cornea, opacities of the lens known as cataracts, degeneration of the retina, and various eye cancers.
Guidance about sun protection is provided by ICNIRP on how to avoid excessive UV exposure for prevention of skin cancer and other UV related diseases. The main ways to protect the skin and eyes are to avoid sun exposure during the middle of the day, seek shade and wear protective clothing including a broad-brimmed hat and sunglasses with side panels. Additionally, broad-spectrum (i.e. protecting both from UVA and UVB) sunscreen with a sun protection factor (SPF) of at least 15+ should be applied adequately and reapplied after sweating, swimming or after prolonged sun exposure. Babies and young children especially should be well protected from intense sun.
In outdoor occupational settings, ICNIRP recommends standard protective clothing and the application of a broad-spectrum sunscreen that is needed to protect outdoor workers. Account should be taken of a range of factors such as type of work and UV surface reflectance in the work environment. For indoor workers exposed to artificial sources such as UVC-emitting lamps for sterilizing or UV lasers, safety precautions include structural measures, administrative controls and personal protective equipment. Individual workers should be made fully aware of the risks of excessive UV exposure.