The concept of SPF (Sun Protection Factor) was first proposed by Franz Greiter in 1946 as an attempt to measure the amount of time it would take an individual to burn with versus without sunscreen. For example, if a person generally burns after a UVB exposure of 20 minutes without sunscreen then if he wears an SPF 15 sunscreen he would burn only after 20 x 15 = 300 minutes!
Unfortunately, the concept is still poorly understood (and has since been largely a marketing ploy) mostly due to the fact that the scale used to measure SPF is LOGARITHMIC rather than LINEAR. Scientists and mathematicians understand this type of scale, but, the general public may never have even heard of the term logarithmic and, thus, will generally assume that the SPF numbers they see on sunscreen bottles are linear in nature. Linear in this context would simply mean that as the SPF number increases the actual protection increases the same amount. This is definitely NOT how the SPF scale works or is measured. In fact, as the SPF increases the increase in protection gets smaller…dramatically!
As the chart and graph show, once the SPF reaches 15 there is very little further protection to be gained from increasing SPF. In fact, an SPF of 15 absorbs 93.3% of UVB rays and an SPF 50 absorbs only 4.7% more. Indeed, from SPF 15 to 30 the SPF has doubled while the UVB absorption has only increased by 3.4% and with an SPF of 50 which is almost another double, the UVB absorption increases only 1.3%. This relationship is known as a logarithmic one and is widely misunderstood. (Several methodologies of SPF measurement exist for UVB absorption and the science behind these is developing, but, all are imperfect and complex with many confounding factors such as incorrect sunscreen use, water exposure, failure to reapply, concurrent use of certain medications and genetic factors).
This misunderstanding is widely known in the world of sunscreen manufacturers, but, has been exploited by companies trying to gain market share in a very competitive industry. All sunscreens that make SPF claims must undergo standard tests as required by the FDA in order to be legally marketed and sold in the US. However, many consumers use significantly less sunscreen than recommended and, thus, may experience underperformance. For a normal human adult face the application of ¼ to 1/3 of a teaspoon is recommended.
As the SPF increases the increase in UVB absorption becomes negligible at 15.
SPF protection does not increase proportionally with an increased SPF number. An SPF of 15 absorbs 93% of the sun’s harmful ultraviolet radiation, while an SPF of 30 absorbs 97%. That is only 4% more absorption of the sun’s harmful rays with an increase of 15 SPF. SPF 50? It absorbs 98% of the sun’s harmful rays.
The unique patented formulation of Sunsect is a waterproof oil-in-water emulsion that is designed to provide protection from the ravages of the sun while at the same time offering long lasting deterrence from biting insects.