Glossary · Clinical
A measure of protection against the UVB rays that cause sunburn. It is traditionally measured on volunteers to ISO 24444; ISO 23675 and ISO 23698 add newer methods for determining SPF without sunburning volunteers.
Clinical and instrumental data turn a marketing promise into a claim you can defend with regulators, retailers and consumers.
Guires CSL formulation, testing, clinical and regulatory teams work with SPF on client projects every week, from the first brief to the final product file.
Sun protectionRelated terms
A supervised patch test on volunteers with repeated applications over about three weeks, a rest period and a final challenge, used to check that a product does not cause irritation or sensitisation under exaggerated use..
Read definition →The rate at which water evaporates through the stratum corneum, measured with instruments such as a Tewameter.
Read definition →An instrument that measures skin surface hydration by electrical capacitance, used to substantiate moisturising claims such as 24-hour hydration..
Read definition →Protection against the longer UV rays linked to skin ageing.
Read definition →Regulations and standards are listed first, then peer-reviewed literature. Sources checked October 2026.
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