Side-effects of the solar radiation.
Although the sun is the primary source of life, overexposure to sunlight is harmful
and in a long term potentially lethal. The spectrum of  solar energy, apart from the bright visible light, includes ultraviolet (UV)
invisible radiation. The later plays a key role in our skin health. UV rays can promote
vitamin D production in the body, in cases
of reasonable exposure to them. On the other hand, serious or life-threatening problems
can be caused because of overexposure. These include skin photo-aging, collagen and DNA damage, skin burns, actinic keratosis, squamous cell carcinoma, basal cell carcinoma and melanoma, the latest being the most aggressive
skin cancer.
In moderate exposure of the body, the UV triggers natural
tanning, which is the increase of skin melanin. This is the pigment that gives the
characteristic color to the skin and it is considered a defensive means against
photochemical damage caused by the sunlight. Immunity can be compromised due to excessive
exposure to the UV radiation.
Types of ultra violet radiation.
The ultraviolet spectrum is divided in three different bands; the UVA, UVB and UVC
radiation.
 UVA is the most commonly encountered type of UV light, since it
occupies nearly the 99% of total such solar energy. Although it is not as harmful as the
UVB and does not cause burns, it penetrates deeply in the skin, leading to extrinsic
aging. The UVA may contribute to the development of cancer, because it damages the DNA
structure. Along with the UVB, it helps in the manufacture of vitamin D within the
body.
UVB is the most dangerous form of the ultra violet solar
radiation, despite the fact that a huge percentage of this is absorbed by the ozone layer in the upper atmosphere. Reasonable
but repeated exposure can result in tanning. Prolonged exposure can cause redness,
increase of temperature on the surface of the skin and serious sunburns. Alteration of
the DNA chain, nevi, actinic keratosis
and squamous cell carcinoma can be the aftermaths of chronic exposure. In general, the
UVB results in skin extrinsic aging, because it
damages the collagen which is the most important structural element. Apart from the skin,
the UVB can harm the eyes by leading to cataract and other conditions.
UVC is of minimal importance, since it is totally absorbed in the
atmosphere and does not reach the surface of the Earth.
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