SPF is an abbreviation for sun-protection factor. It is expressed in numbers such as 20, 30 or 75. These values indicate the degree of protection from sunburn given by good sunscreens. This value is related to the sum amount of sun contact rather than a simple implication of the length of the exposure to the sun. It is a typical error to assume that the duration of a particular sunscreen’s effectiveness can be calculated by simply through the multiplication of the sun protection factor by t the length of time that it will take one to suffer from sunburn without the protection of a sunscreen. This is due to the fact that the amount of sun contact a person gets is based on more than just the span of time spent under the sun. The quantity of sun contact is based upon several factors which includes the duration of contact, geographic location, time of the day and weather conditions.
A particular sunscreen’s SPF value is determined by getting the ratio of the energy needed to generate a minimal erythma dose (minimal sunburn or skin reddening) through the sunscreen, in contrast to the energy needed to make the similar reaction without the presence of a sunscreen.
For instance, a person who experiences sunburns after being exposed to the sun for 30 minutes could, in theory, lengthen the duration of time until a burn starts to 3 hours with the use of a sunscreen with a sun protection factor of 4. But the same individual utilizing the sunscreen having a sun protection factor of 30 (which translates in theory, to 15 hours of sunburn protection) may not be actually guarded from UV-induced erythema for the whole day of spontaneous exposure to the sun.
As a helpful tip, always wear a sunscreen with an SPF 15 or higher when expected to get exposed to the sun.
