Ultraviolet A (UVA) and Ultraviolet B (UVB) - Ultraviolet Rays explained.

Why in news?

Scientists at IIT Bombay have developed a New Sun Screen Lotion made of Engineered Zinc Oxide Nanoparticles (E-ZnO NPs) which can better manage UVA rays

History
Initially only UVB were considered harmful. Then researches proved that even UVA are harmful. And now latest by IIT Bombay that even sun screens at present are not effective. 

Information about ultraviolet A (long-wave) and ultraviolet B (shortwave) rays

• 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 With even shorter rays, most UVC is absorbed by the ozone layer and does not reach the earth.

Harmful effects of UV rays

• Both UVA and UVB, however, penetrate the atmosphere and play an important role in conditions such as premature skin aging, eye damage (including cataracts), and skin cancers and they also suppress the immune system
• By damaging the skin's cellular DNA, excessive UV radiation produces genetic mutations that can lead to skin cancer. 
• World Health Organisation has identified UV as a proven human carcinogen. 
• UV radiation is considered the main cause of nonmelanoma skin cancers (NMSC)
• 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.
• Recent studies show that UVA, which penetrates the skin more deeply than UVB,causes skin aging and wrinkling (photoaging), significant damage in areas of the epidermis (outermost skin layer) and basal layer of epidermis where most skin cancers occur by damaging skin cells called keratinocytes.
• A tan results from injury to the skin's DNA; the skin darkens in an imperfect attempt to prevent further DNA damage. These imperfections, or mutations, can lead to skin cancer.

Sun Protection Factor

Since the advent of modern sunscreens, a sunscreen's efficacy has been measured by its sun protection factor, or SPF. SPF is not an amount of protection per se. Rather, it indicates how long it will take for UVB rays to redden skin when using a sunscreen, compared to how long skin would take to redden without the product. For instance, someone using a sunscreen with an SPF of 15 will take 15 times longer to redden than without the sunscreen. If you follow our comprehensive Prevention Guidelines, you can enjoy yourself outdoors while staying protected from both UVA and UVB year-round, whatever the weather, wherever your locale.