When is it necessary to protect yourself from too much sun? When can sun cause long-term damage? The current recommendation of the World Health Organization is: If the UV index for the day is above 3, we should reach for sunscreen and co. Researchers from Australia and New Zealand have now shown that even weak UV radiation attacks our skin to an alarming degree.
The basics
The UV index, as Richard L. McKenzie of the National Institute of Water & Atmospheric Research, New Zealand, and Robyn M. Lucas of the National Centre for Epidemiology and Population Health at the Australian National University explain, shows when the sun shines so strongly that our skin would be damaged after an hour without protection. Now, few people stay outside for an hour or less when the weather is nice. Especially when playing on the playground, at the beach or doing sports, time flies by.
The type of radiation to which our skin is particularly sensitive is called erythemal UV radiation. It is expressed in Standard Erythemal Doses (SED), with light skin types showing damage such as skin redness after 24 hours at radiation levels as low as 2 to 2.5 SED.
According to the scientists, it has been proven that our skin suffers just as much damage after a short period of exposure to a high UV index value as it does when exposed to lower-grade UV radiation over a longer period of time. Long-term damage therefore also occurs with less sun. So dosage must always be considered in relation to duration.
What was studied
In their study, Richard L. McKenzie and Robyn M. Lucas looked at how the UVI and SED interact.
To do this, the two scientists and their teams compared the reported UV index for the city of Lauder in New Zealand with Melbourne in Australia and other cities, and analyzed how the corresponding SED develops over the course of the day.
The results
For the Lauder location studied, the SED fell below the safe level of 2.5 for fair-skinned people on only one day, although the number of days on which the UVI was reported as below 3 was much higher. Even with low UVI, the SED value could rise to over 14 over the course of the day.
McKenzie and Lucas compared this with cities at other latitudes to rule out the possibility that it was a local phenomenon. They found that the relationship between UVI and SED is the same everywhere.
Long-term damage in weak sunlight: what does it mean?
So on days when the peak UVI remains below 3 but the SED daily dose rises well above the threshold, exposed areas of the body such as the neck and face are at particular risk because we underestimate the strength of the sun and risk long-term damage. The study states that in mid-latitude regions, i.e. here in Europe, people need to be particularly careful. In the winter months, the UV index is usually not only below 3, but even below 1. The SED also rarely rises above 2.5. In spring or fall, when the sun is already stronger, we do not take sun protection very seriously. Yet the dose of UV radiation we expose our skin to during these transitional periods is, according to the research team, mathematically three times higher than on days with high UVI, when sunscreen and protective measures are taken for granted by many. So this ignorance increases our risk for skin cancer many times over.
Thoughtful protection, even when the sun is low
McKenzie and Lucas therefore recommend dispensing entirely with references to the fact that protection is not necessary when the UVI is less than 3, and including precisely the power of the radiation in the form of the SED value in addition to the radiation dose. They suggest replacing this information with behavioral recommendations that address when we should spend time in the sun during the day, for how long, and with what protection.
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