The sunlight that reaches the earth is made up of two types of harmful rays:
Long wave ultraviolet A (UVA) that can age us
Short wave ultraviolet B (UVB) that can burn us
Overexposure to either of these can damage the skin.
There is a third type of UV rays, called UVC, but although they are the shortest and strongest of the three, they are almost completely absorbed by the ozone layer and therefore do not affect the skin.
UVA rays account for 95% of the UV radiation reaching the Earth and are present with relatively equal intensity during all daylight hours throughout the year. UVA rays can penetrate both clouds and glass. They go deep into the dermis and lead to premature skin aging, wrinkling and suppression of the immune system. The latest research show that UVA radiation may directly cause some skin cancers, including melanomas.
UVB will usually burn the superficial layers of your skin and is the main cause of skin reddening and sunburn. The intensity of UVB rays vary by season, location and time of day, with 10AM to 4PM being the peak hours.
While Sun Protection Factor (SPF) is the universal measurement of UVB protection, no comparable standard exist for UVA, since it does not cause reddening of the skin. Conventional sunscreen blocks very little UVA radiation, relative to the nominal SPF. However, Broad-spectrum sunscreens are designed to protect against both UVA and UVB, but do not guarantee protection against all UVA wavelengths.
The Ultraviolet Protection Factor (UPF) rating indicates how effective a fabric is at blocking out solar ultraviolet radiation. Unlike SPF, which is a measure of only UVB protection, UPF rates protection against both UVA and UVB radiation.
Exposure to the sun is inevitable, but you can take precautions and protect yourself and your loved ones from sun damage.