 | | SPF Sun Protection Factor
In the United States the Sun Protection Factor (SPF) of a product tells how long you can stay in the sun without burning from UVB light.
This is a sunburn meter and often products inadvertently allow tanning with enough sun exposure.
UVA light has not been formally tested for the FDA to acquire a SPF rating but manufactures commonly include them in a broad sunscreen or sunblock. SPF is the amount of time before your skin burns and UPF (Ultraviolet Protection Factor) is the amount of sun blocked by fabric.
SPF means Sun Protection Factor using this equation.
- Take the time you would normally burn in the sun without protection. 20 minutes will normally produce redness on a light skinned individual.
- Multiply the number by the SPF of your product. Example: with an SPF 15 x 20 minutes of sun time = 300 … is how many minutes you can stay in the sun without burning. 300 minutes divided by 1 hour of 60 minutes = 5 hours of sun protection without a sunburn.
How SPF is determined
In a controlled indoor laboratory eliminating any effects of environmental change, i.e. wind, heat, and cold, with untanned test subjects put through a two day test.
- On the first day the lower back is protected except for the test site and exposed to UVB light until mildly red.
- On the second day a sunscreen or sunblock is applied to a new test site and exposed to UVB light until the same mild redness occurs.
- The amount of time to achieve redness with the applied sunscreen or sunblock determines the SPF. As people vary so will the sun protection of products… results vary with individuals.
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