What is UV Radiation, its relation to Skin Health and Global Warming
Sun light as we know is composed of a spectrum of light with wavelength ranging from 100 Km (Radio waves) to 10-12 nm (Gamma rays). The visible light falls in the range of 300-700 nm starting from violet with lowest wavelength to red light with highest wavelength. The light with wavelength that falls between 200-400 nm which is just before violet color wavelength of visible range is called ultra violet or UV rays.
The UV radiation is further divided into 3 categories: Ultraviolet C (UVC) (220–290 nm), Ultraviolet B (UVB) (290–320 nm) and Ultraviolet A (UVA) (320–400 nm). The primary source of UV radiation is the sun and is composed of approximately 95% UVA and 5% UVB at mid-day (IARC, 2012). Although UVC has the highest energy and the greatest potential to induce damage, it is completely absorbed by ozone in the terrestrial atmosphere and is, therefore, not biologically relevant. UVB and UVA, however, do reach the earth's surface and can impact biological systems.
The longer wavelengths, although with less energy, can penetrate deeper into the biological tissue; therefore, the effects of UVA are evident in deeper layers of the skin and eye than are UVB.
The amount of exposure to UV rays depends on many factors, the most important been the distance travelled by the rays. UV radiation is highest at equator and lowest at the poles so we see that people have darker skin tone at equator and lighter skin tone at the more northern and southern parts of earth. However, the amount of UV radiation at the higher latitudes varies as UVA travels farther than UVB.
Especially important for trekker and mountaineers, as the altitude increases, the intensity of UV radiation increases due to a less dense atmosphere which can absorb the radiation. It has been shown that UV exposure increases by 8% per kilometer of height gained due to the reduced amount of radiation absorbed by atmosphere.
For those who enjoy the summer sun, the sun is at a greater angle during the summer months, resulting in more UV radiation reaching the surface and is highest during noon and, the reverse is true of the winter months.
IMPORTANT: UVA and B radiation is not completely filtered by clouds as well as by clear glass and most of the radiation hits earth’s surface.
Now, let us understand the effects of UV radiation on our skin. When the UV radiation penetrates the epidermis and dermis of our skin, the DNA in the skin cells (keratinocytes, melanocytes and fibroblast) absorbs energy from shorter-wave UV and undergo a modification causing abnormal interactions with other cellular constituents. UV radiation also damages cellular components indirectly, through production of oxidative free radicals. Naturally occurring UV radiation is the environmental mutagen responsible for the largest percentage of induced skin diseases, including redness, irritation and inflammation, premature aging, and cancer. Furthermore, as there is gradual depletion of ozone layer, much of solar UV energy is not absorbed in the stratosphere resulting in higher levels of UV radiation that strikes the surface of the Earth. Increased ambient UV radiation from global climate change may be an important factor to explain the burgeoning prevalence of melanoma and skin cancer over the last several decades.
Premature aging due to UV exposure may account for up to 80% of visible signs of aging in the skin including dry appearance, scalping, wrinkling and impaired pigmentation. It is important to note, however, that the UV exposure and accumulation of DNA damage that underlie melanoma formation begin with sun exposure early in youth, which is why sun protection in the pediatric years is so important. Interestingly, it has been found that more than five sunburns in a lifetime doubles risk for melanoma and there is increased risk for melanoma as a young adult if there are increased sunburns in childhood. The sudden rise in UV induced skin disease is linked to global warming because as the temperature rises the intensity of the UVA and UVB radiation also increases hence the potency of exposure also increases.
The most effective way to protect our skin from damaging UV radiation is to use a good sunscreen and apply it regularly during day time. Other methods include wearing protective clothing, seeking shade while traveling and using good sun glasses which filter/block UV radiation.
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Reference:
Ultraviolet Radiation, Aging and the Skin: Prevention of Damage by Topical cAMP Manipulation, Molecules. 2014 May 15.
The human health effects of ozone depletion and interactions with climate change, Review, Photochem Photobiol Sci. 2011 Feb
