Tuesday, 14 October 2014

The Ultraviolet Radiations and Their Effects

Wikimedia Commons by charles
The electromagnetic or the light spectrum of the sunlight contains ultraviolet or UV radiations of wavelengths shorter than the visible light. These are invisible to the naked eye. It is also produced by an electric arc, hence the welders are expected to cover the eyes. 

These UV rays have different bands like long waves or black light ( UVA ), and medium waves (UVB ), which penetrate the atmosphere of the earth. They cause premature skin aging, cataracts, skin cancers and suppress the immune system, when overexposure occurs.

UVA account for 95 % of the UV radiations reaching the surface of the earth and are less intense than UVB, and can penetrate through clouds and glass. Their intensity is constant throughout the year day and throughout the day. The vitamin D is produced in body due to it, but its overexposure suppresses the immune system, forms cataract and toughens the skin. As compared to UVB, they penetrates more deeply into the skin but does not cause significant damage to epidermis or the outermost skin layer, where most skin cancers appear. It causes skin aging, wrinkling or photo-aging. It is the the tanning ray, but both outdoor or salon tan damage the skin by damaging the skin DNA. About 99.9 %of UVA radiation is blocked by UV film,while sun blocking lotions offer limited protection. 

UVB, the most energetic and destructive form of UV radiations, are completely absorbed by the atmosphere atmospheric ozone layer. But the depletion of ozone layer by the chlorofluorocarbons (CFC), have increased the skin cancer risks. It causes cataracts, photo-aging, skin cancer, reddening of skin, erythema or sunburn and the photochemical damage to cellular DNA by damaging the superficial epidermal layers. Its benefits of its exposure include effective and long-term treatment for eczema, vitiligo, and psoriasis. Its intensity varies according to season, location and the time of the day. It does not penetrate the glass but it strikes the skin with double intensity at high altitudes, snow or ice areas, because 80% of these rays get reflected.

Most of the short wave or germicidal waves (UVC ), are absorbed by the ozone layer and does not reach the earth. 

The amount of melanin in the skin determines the color of the skin. It is the melanin which absorbs the ultraviolet rays. The fair complexioned people have little amount of melanin and are more prone to melanoma, the deadliest skin cancer.

The photochemical effect of UV radiations is increased by chemicals like tetracycline, birth control pills, sulphathiazole, lime oil, antidepressants, anti dandruff shampoos, some cosmetics or sunscreens etc,.

The bright or deeply dark colored and lustrous clothes reflect UV radiations more than pastels or bleached cotton, while the loose fitting or closely woven clothes block the sunlight from touching the skin. Also the broad brimmed hats and UV sunglasses protect the neck,head, and eyes.