SPF- Sun Protection Factor
To understand SPF, first, we understand ultraviolet (UV) radiation. UV rays are the type of light that reaches the earth from the sun that is invisible to the naked eye. For simplification purposes, I will refer to these wavelengths as they are classified -UVA and UVB rays. Both UVA and UVB rays will penetrate the atmosphere and can contribute to conditions such as premature skin aging and skin cancers. Further, UVA and UVB rays play a part in suppressing the immune system making it more difficult for your body to fight off these and other disease states. UVA rays will penetrate to the deeper layers of the skin where UVB rays will usually burn the superficial layers of your skin.
The SPF- sun protective factor is not actually a protective factor per se but rather a relative measure of how long it will take for UVB rays to redden the skin when wearing a sunscreen. For instance, if it takes someone to turn red in the sun 20 minutes then an SPF of 30 will protect for 10 hours. What most people don’t take into consideration, however, is that UVB rays are going to vary during the day and by location. Also, how often someone reapplies is not taken into account in the sun protection factor.