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Study reports that sunburn can still happen, even if the UV index is below 3.
This was an exposure study analysing ultraviolet radiation (UVR) measurement data collected in Germany from nine monitoring stations over ten years. The authors used the measurement data to explore the potential for receiving UV doses that would lead to erythema (sunburn) for fair skin (Fitzpatrick skin type II) people on days where the ultraviolet index (UVI) had a median value of 2 or less. Current UV protection advice given by the World Health Organisation (WHO) states that no protection is needed when the UVI is under 3. The authors reported that on days with UVIs of 1 or 2, sunburn could occur in a matter of hours around solar noon in summer and was also possible in winter over a longer exposure period.
The authors pointed to some limitations in the exposure and dose assessments within the study. These included comparing human exposure to the horizontally oriented flat design of the UV detectors, assigning the dose needed for sunburn to fair skin people without taking account variations within this group and not allowing for higher resistance to erythema caused by previous exposure. However, the largest uncertainty was around human exposure caused by individual behaviour in regard to aspects like clothing, shade and indoor activities.
The large dataset analysed in this study was a key strength in being able to categorise UV exposure over a long period of time and account for seasonal variability. Despite some of the limitations described by the authors, the study showed that, at least theoretically, sunburn could occur when the UVI is below 3 during extended periods outdoors. Although the WHO and leading radiation bodies such as ARPANSA apply the UVI model to communicate risk for solar UV protection, Cancer Council Australia has recently recommended that the application of sunscreen should be part of everyone’s daily routine if the UVI is above 3 or for extended periods outdoors at lower UVIs.