Where, how, and when to go out in the sun

Every spring, newspapers, magazines and websites are full of recommendations for risk-free sunbathing, with particular reference to the times of day to go out into the sun. There are contradictory points of view, however, even among the most authoritative international scientific institutions. Some say to be careful when the sun is directly overhead, others recommend staying in the shade from 10 am to 5 pm, others from 11 am to 3 am. One thing is certain: the highest levels of radiation occur from 10 am to 4 pm, and to work out how strong the sun’s rays are, the American Cancer Society suggests the “shadow test”: if our shadow is shorter than we are, it means that the sun is still overhead and so it is essential to be properly protected.

How we should act depends on several factors, in addition to the skin phototype, and these need to be taken into consideration using common sense, here are the main ones:


It goes without saying that a walk in the park at noon on a fine winter’s day won’t put anyone at risk of sunburn, it’s a different matter in the spring when the first warm, sunny days can catch people with lighter phototypes off guard and even in April they can get sunburnt just walking around in urban spaces. It is essential for everyone to take care in the hottest season, which in the northern hemisphere is May to September and in the southern hemisphere is November to March.


The effects of exposure to the sun are greater at high altitudes because there is less atmosphere to absorb the harmful UV radiation. Here it is necessary to be well protected from the sun all year round, even in winter, because snow reflects the sun’s rays like sand or water do, increasing exposure to radiation. It is estimated that snow reflects 75 percent of the sun’s rays that cause sunburn, while sand reflects 15 percent, concrete 10 percent and sea spray 25 percent.


The distance we are from the equator is also a factor that changes the level of protection needed and the times of day when it is safe to go out in the sun. This is due to the ozone layer: the more perpendicular the sun’s rays are to the earth’s surface, the thinner it is, and the more UV radiation passes through. It follows that sun safety recommendations cannot be the same for the beach in Brighton, UK, and for an atoll in the Maldives Islands.

Weather conditions

If the sun is covered by a thick layer of black clouds, like summer showers and thunderstorms, it is unlikely to be harmful. On the other hand, compact cloud cover lets 30-40 percent of UV rays through. When clouds alternate with patches of clear sky, the UV radiation levels can increase greatly, reaching 80 percent if the sky is only half-covered.

This makes it easier to get sunburnt in these conditions because we tend to underestimate exposure times compared to when the sky is clear.

UV Index Forecasts

The growing awareness of the risks of excessive exposure to the sun has prompted many newspapers and media outlets to publish the levels of UV radiation alongside traditional weather forecasts. This is what they mean:

  • Low UV index: no protection is needed, even in the middle of the day.
  • Moderate UV index: apply sunscreen and wear a hat if you are out in the sun a lot, especially in the middle of the day.
  • High UV index: apply sunscreen that is at least factor 15 every two hours, wear a hat and sunglasses, stay in the shade during the middle of the day.
  • Very high UV index: follow the instructions in the previous point even more closely.