Overexposure to ultraviolet (UV) radiation is the main modifiable risk factor for skin cancer. The Global Solar Ultraviolet Index (UVI) was introduced as a tool to visualize the intensity of UV radiation on a certain day, which should enable and encourage people to take appropriate protective measures. The ‘low’ exposure category of the UVI, defined by a rounded UVI value of 0, 1 or 2, was linked to the health message ‘No protection required’ by the World Health Organization and partner organizations. However, published evidence corroborating this advice is not available. To evaluate the erythemal risk of low UVI days, we analyzed 14,431 daily time series of ambient erythemal irradiance data measured at nine stations of the German solar UV monitoring network during the years 2007–2016. We analyzed the proportion of days in the sample for which ambient erythemal doses calculated for various time intervals exceed average minimal erythemal doses (MEDs) of the Fitzpatrick skin phototypes I–VI to assess the potential for erythema arising from sun exposure on days with low UVI values. Additionally, we calculated for each day the minimum exposure duration needed to receive one MED. Our results indicate that on days with a UVI value of 0, risk of erythema is indeed negligible. Conversely, the abovementioned health message appears misleading when melano-compromised individuals (skin type I and II) spend more than 1.5 hours outdoors on days with a UVI value of 2. Under rare circumstances of prolonged exposure, MEDs of the two most sensitive skin types can also be exceeded even on days with a UVI value of 1. Hence, current WHO guidance for sun protection on days with low UVI values needs reconsideration.

Introduction (Over)exposure to ultraviolet radiation is a major risk factor for skin cancer. The Global Solar Ultraviolet Index (UVI) was introduced by the WHO and partner organisations in 1995 as a simple measure of the intensity of solar UV radiation, providing guidance for the population to use appropriate sun protective measures. Little is known about the impact of the UVI on actual sun protection behaviour. Our systematic review aims to assess global levels of awareness, understanding and use of the UVI as prerequisites for the preventive effectiveness of this public health tool. Methods and analysis Systematic searches will be performed in 10 electronic literature databases including Medline, Scopus and Web of Science–Core Collection, two clinical trials registries and at least two grey literature databases (OpenGrey, Bielefeld Academic Search Engine). Additional literature sources will be retrieved using hand search of reference lists of included studies and snowballing methods. We will include studies with all types of quantitative study designs and participants reporting on at least one outcome in the three main categories (i) awareness, (ii) understanding and (iii) use of the UVI. We will assess the risk of bias within studies with an abbreviated version of the AXIS tool, designed specifically for cross-sectional studies. As we expect large heterogeneity in outcomes, we will conduct a narrative synthesis of results instead of a meta-analysis. Ethics and dissemination Ethical approval and patient consent are not required as this is a systematic review based on published studies. The results of this study will be published in an international peer-reviewed journal. Prospero registration number CRD42018093693.

Thirty years ago, the Global Solar UV Index (UVI) has been introduced as a health promotion instrument to improve sun protection. We assessed systematically global levels of awareness and use of the UVI as a prerequisite for the preventive effectiveness of this public health tool. We conducted a comprehensive literature search across 10 databases, including PubMed, Scopus and Web of Science Core Collection, as well as clinical trial registries and gray literature databases. The risk of bias of studies was evaluated using the Joanna Briggs Institute checklist for prevalence studies. In addition to narrative and descriptive analysis, we performed meta‐analyses with geographical subgroup analyses to statistically summarize the results. In total, we identified 40 publications from 39 different studies across multiple global regions. However, the number of studies in the analyses varies depending on the outcome. The results, especially the awareness of the UVI, were largely dependent on the specific geographical location of the studies. While the prevalence of awareness of the UVI is high among Australian populations, there is considerable variability in levels of awareness across other global regions. At the same time, the use of the UVI is at a low level across all regions, demonstrating the need for enhanced dissemination of knowledge about the perils associated with ultraviolet radiation and the advantages of using the UVI.

Overexposure to ultraviolet (UV) radiation is the main modifiable risk factor for skin cancer. The Global Solar Ultraviolet Index (UVI) was introduced as a tool to visualize the intensity of UV radiation on a certain day which should enable and encourage people to take appropriate protective measures. The exposure category ‘low’ of the UVI, including values from 0 to 2, was linked to the health message ‘No protection required’ by the World Health Organization and collaborating centres. However, published evidence corroborating this advice is scarce. Therefore, we analysed ambient erythemal irradiance data of 14,431 daily UVI time series of low UVI days. Data were gathered at nine stations of the German solar UV monitoring networkcovering all major climate areas in Germanyin the years 2007–2016. We compared ambient erythemal doses calculated for various time intervals with average minimal erythemal doses (MEDs) of the Caucasian Fitzpatrick skin phototypes I-IV to assess the potential for skin damage arising from sun exposure on days with low UVI values. The most common months for the occurrence of days with low UVI values in our dataset were January and December, February and November, and March and October for UVI 0, 1 and 2, respectively. Our results indicate that on days with a UVI value of 0, risk of deterministic radiation injury (solar erythema) is negligible. Conversely, the above-mentioned health message appears misleading when melano-compromised individuals spend several hours outdoors on days with a UVI value of 2, as median doses exceed the MEDs of Fitzpatrick skin types I and II after an exposure duration of only 2 h around solar noon. Under very rare specific circumstances, MEDs of those two most sensitive skin types can also be exceeded even on days with UVI 1. Hence, two aspects of current public health messages may need reconsideration: on the one hand, the health message related to an ‘innocuous level’ of the UVI and, on the other hand, a possible adaption of UVI-related health messages to different skin types.

A Global Solar Ultraviolet Index (UVI) value of 2 is generally linked to the health message ‘You can safely stay outside!’ To examine whether this is sound advice for all skin types and even for prolonged periods spent outside we used erythemal irradiance data of all 136 days during the study period from 2014 till 2016 with such a UVI measured by the German Federal Office for Radiation Protection (BfS) in Munich, Germany. A comparison between the ambient erythemal doses calculated for various time intervals and minimal erythemal doses (MEDs) of the Caucasian skin types I–IV led us to a critical reappraisal of the above health message. Specifically, the message might be misleading if people with a fair complexion want to spend several hours outside, because without any protective measures the doses received can be sufficient to induce erythema. We thus recommend an amendment of the health message related to a safe level of the UVI and, moreover, generally tailoring UVI-related health messages to different skin types. Currently, these messages do not seem to be strictly evidence based, which might be one reason for the unexpected result of our analysis.