According to The CDC, UV rays cause 60-90 percent of melanomas, the most dangerous type of skin cancer. Yet in spite of public health warnings, two-thirds of people between 15-29% admit to getting at least one serious sunburn a summer, says a survey from the Danish Cancer Society. Choosing a sunscreen for outdoor days is essential and here’s what you should know about SPF.
SPF stands for sun protection factor, but it specifically indicates protection against the ultraviolet B (UVB) rays that cause sunburn. The SPF number indicates how well a sunscreen protects skin against sunburn. It is not an indicator of how long you can stay out in the sun, rather, it indicates how much longer it takes untanned skin to begin to redden with sunscreen.
To work out the SPF of a sunscreen, laboratory tests on a minimum of 10 human volunteers liberally apply sunscreen to an untanned area of the skin (typically the buttocks), which is then exposed to simulated sunlight via UV lamps. Measurements are taken of how long it takes the skin to get a minimal burn when covered with sunscreen, and how long it takes to get the same minimal redness without it.
The FDA requirements for how to apply sunscreen to the test subject is stated as
- Apply sunscreen using a finger cot to spread as evenly as possible. Presaturation of the finger cot (i.e., soaking the finger cot in the sunscreen before application) is not required.
- Apply sunscreen in a specified amount: 2 mg/cm2.
- Wait at least 15 minutes after applying the sunscreen before UV exposure.
If you really want to know… What is the sunscreen standard for use in the SPF Test?
Answer: 21 CFR 201.327(i)(2) requires the use of a 7-percent padimate O and 3-percent oxybenzone sunscreen standard formulation in the SPF test.
When it comes to a sunscreen’s SPF, is bigger really better?
Although the differences in SPF values seem large, there’s actually very little difference between how much UVB they filter. SPF 50+ filters 98% of UVB, compared with 96.7% filtered by an SPF 30 sunscreen. And an SPF 30 sunscreen applied properly will give better protection than an SPF 50+ sunscreen applied too thinly or not frequently enough.
UV radiation can always get through to the skin, no matter how high the SPF. No sunscreen can ever block sunburn and associated skin damage completely, sunscreen is only one part of effective sun protection. Finding shade, wearing protective clothing and a wide brim hat are recommended for days in the sun.