UVB Protection (SPF)
SPF is a measure of UVB protection. It does not indicate the level of protection from UVA.
SPF stands for Sun Protection Factor. It’s a measurement of redness (Minimal Erythemal Dose, for those of you interested in the professional term). It is how long you can stay in the sun before getting burned.
An SPF 5 means you can stay in the sun 5 times longer (with the sunscreen) before burning. Say you normally burn in 10 min. If you apply an SPF 5, you can stay in the sun 5 times longer than 10 minutes before burning. In other words, 50 minutes (5 x 10 min).
SPF effectiveness tapers off after SPF 30. It does not increase linearly. In other words, SPF 100 will not allow you to stay in the sun 100 times as long. For example, SPF 15 will block about 92% of rays, while SPF 30 blocks about 97% of UVB rays. So, a higher SPF does not translate to an equally higher level of protection.
Also, layering a moisturizer with SPF 30 and makeup with SPF 15 does not give you a total protection of SPF 45. The SPF is not additive. The combined SPF is less in most cases.
The FDA is currently evaluating a proposed regulation to limit the SPF value to 50. Anything above SPF 50 would have to be labeled “SPF 50+.”
At a minimum, you need an SPF 15 to protect yourself from skin cancer. Anything below SPF 15 will only protect against sunburn; it will NOT reduce the risk of skin cancer or skin aging.
Most dermatologists and estheticians today recommend using a minimum of SPF 30.