Twenty-five studies (28,412 participants) were included: three RCTs, two non-randomised intervention studies and 20 cross-sectional studies. One RCT was rated as strong quality, one as moderate and one as weak. The two non-randomised intervention studies were rated as moderate and weak. Sixteen cross-sectional studies were rated as weak and four were rated as moderate.
Familiarity: Ultraviolet Index awareness (21 studies) varied considerably between countries with very low levels in Germany and Sweden and high levels in some recent Australian studies. Estimates obtained from strong or moderate studies ranged from 27% to 53%. Understanding of the Ultraviolet Index was found to be considerably less prevalent. When only studies rated strong or moderate were considered, estimates ranged from 17% to 55%. Generally, the percentage of the population that claimed to understand the Ultraviolet Index was greater than the percentage who could correctly describe or interpret it.
Knowledge and attitude: Three studies measured self-reported knowledge about ultraviolet radiation and skin cancer. Studies classified as strong or moderate suggested that the Ultraviolet Index had no influence on either outcome.
Behaviour: The impact of the Ultraviolet Index on sun protection behavior was explored by three RCTs and 11 cross-sectional studies. Studies collected data on general sun protection, protective clothing and sunscreen. Strong and moderate studies suggested that the Ultraviolet Index exerted no or only a limited influence on sun protection behaviours. Many people who claimed to use the Ultraviolet Index did not consider it regularly to plan their sun protection.
Sun exposure: Three RCTs and three cross-sectional studies examined sun exposure; one RCT was considered flawed due to use of apparently faulty ultraviolet light meters that gave erroneous readings. Based on strong and moderate studies, the Ultraviolet Index did not appear to influence sun exposure.