Ultraviolet radiation is classified by wavelength into three regions:
UVA – is thought to contribute to premature aging and wrinkling of the skin and has recently been implicated as a cause of skin cancer.
UVB – more dangerous than UVA and has been implicated as the major cause of skin cancers, sun burning and cataracts.
UVC – is extremely dangerous but does not reach the earth’s surface due to absorption in the atmosphere.
Ultra Violet Protection Factor (UPF)- this rating indicates how much UVR is blocked by a material. For example, a material with a UPF rating of 20 would only allow 1/20th of the hazardous
UVR falling on its surface to pass through it.
This means that this material would reduce the UVR exposure by a factor of 20.
Stated another way, this material would block 95% of the UVR and transmit only 5%. UPF 50+ blocks more than 98%.
Sun Protection Factor (SPF)- this rating is used for sunscreens, which refers to the blocking strength of the sunscreen and the length of time it protects. For example, a SPF of 50 will allow you and your child to stay in the sun 50 times longer than the normal time it takes unprotected skin to change color (tan) or burn. If your skin burns in 10 minutes, than your protection will last up to 500 minutes (multiply 50 by 10).
Sunscreen should be applied 30 minutes before going out in the sun, because the chemicals need time to absorb into the skin. The best sunscreen to choose has broad-spectrum protection that can block out both UVA and UVB rays.