Raise Your SPF IQ!

I am often asked by clients and others about SPF, so I will be doing a series on the subject to increase awareness (and protection!).

Sun Protection Factor

The SPF is the amount of UV radiation required to cause sunburn on skin with the sunscreen on, as a multiple of the amount required without the sunscreen. There is a popular oversimplification of how SPF determines how long one can stay in the sun. For example, many users believe that, if they normally sunburn in one hour, then an SPF 15 sunscreen allows them to stay in the sun fifteen hours (i.e. fifteen times longer) without getting a sunburn. This would be true if the intensity of UV radiation were the same for the whole fifteen hours as in the one hour, but this is not normally the case. Intensity of solar radiation varies considerably with time of day as well as location.

In practice, the protection from a particular sunscreen depends, besides on SPF, on factors such as:

- The skin type of the user.

- The amount applied and frequency of re-application.

- Activities in which one engages (for example, swimming).

- Amount of sunscreen the skin has absorbed.

Next: Proper Application of SPF...