The consumer is repeatedly told to use sunscreen to stave of skin cancer. In the event it is often assumed that the higher the SPF (Sun Protection Factor) of the product, the more effective it is. But is it true that 50 SPF is necessarily twice and good as SPF 25 and that SPF 75 is three times as good?
It does not work quite like that, it would seem. The SPF is indicative of how much time a person can spend in the sun without burning with sunscreen on as opposed to without sunscreen being applied.
The SPF is not indicative of how much UV radiation the product is able to block. In fact a higher SPF may block only a tiny amount of radiation from the sun than a far lower SPF sun block.
In fact we now even have sun blocks that claim to be 100 SPF and even beyond that, which is actually misleading to people. It is now proposed by the FDA that labeling of sunscreen be amended and that stated SPF be capped at 50+ so that you don’t have people being misled with absurd claims.
Also SPF refers only to UVB protection or protection against sunburn. UVA rays actually cause deeper damage (leading to skin cancer), which should also be kept in mind.
Source: Boston
