Radiation at the longer UV wavelengths of 320-400 nm, called UV-A, plays a helpful and essential role in the formation of Vitamin D by the skin and plays a harmful role in that it causes sunburn on human skin and cataracts in our eyes.
The incoming radiation at shorter wavelengths, 290-320 nm, falls within the UV-B part of the electromagnetic spectrum.UV-B causes damage at the molecular level to the fundamental building block of life' deoxyribonucleic acid (DNA).
The higher the number on the UVI index, the higher the radiation level. A UV Index of 3 or more requires protection from the sun. At this level, UV levels are enough to damage the skin and increase the risk of skin cancer.
When UV rays reach your skin, they interact with a natural chemical in the skin called melanin. Melanin is your first line of protection and absorbs UV rays in order to shield your skin against sun damage; this chemical reaction is what gives skin a tan. When the amount of UV rays you're exposed to exceeds the protection provided by melanin, however, you get a sunburn.
Repeated overexposure to UV rays can lead to various forms of skin damage including:
- Fine lines
- Age spots, freckles, and other discolourations
- Scaly red patches, called actinic keratoses, thought to be the beginnings of skin cancer
- Tough, leathery skin that feels and looks dry and rough