Behind every printed number sits a test with a written method and a stated uncertainty
What an in vivo SPF test actually involves, how UVA protection is measured in vitro, the ISO standards behind the figures, and what a claim substantiation file has to hold.
What an in vivo SPF test actually involves
A panel of human volunteers, a weighed quantity of product, a solar simulator and a graded visual endpoint. The single integer on a pack is the compressed result of a long procedure.
Standards · 13 minIn vitro UVA testing: how the figure behind the circled mark is produced
The ultraviolet A determination is made on a roughened plate rather than on skin, with a pre-irradiation step that has no equivalent in the SPF test.
Standards · 12 minThe ISO standards behind the numbers, and what a standard actually is
A test standard is a written method, agreed internationally, that makes results comparable. It is not law, it is not a licence, and referencing one is not the same as complying with it.
Standards · 12 minMeasurement uncertainty: what a tested figure is before it becomes an integer
A protection factor is a panel mean with a confidence interval. The pack prints a rounded down integer, and everything about the precision of the measurement is discarded at that point.
Standards · 12 minClaim substantiation: what has to be held, by whom, and what adequate means
Every claim on a sun protection product has to be supported by evidence held before the claim is made. The file sits with the responsible person and is available to enforcement authorities.
Standards · 12 minThe wording note
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