How much sun is too much?
We all know that too much sun is bad for your skin. But how do you know how long you can stay in the sun? You can't see or feel UV light, so it's difficult to know how strong it is and what effect it will have. Summer heat isn't a good indicator here because UV radiation might also be present when it's cold outside. This is because heat from the sun doesn't come from UV light, but from infrared light in the sun’s rays.
The higher in the sky the sun is, the stronger the UVB radiation on Earth. This is both true in terms of the sun’s position over the course of the day – it's highest at midday – and in terms of geographical location. So UV radiation is particularly high close to the equator, for instance in Florida, Thailand or Central America. It is also high in Australia and New Zealand because these countries are near the hole in the ozone layer above the Antarctic. The thinner the ozone layer, the stronger the UV radiation levels.
UVB exposure tends to be more of a problem in mountainous regions than in lower regions. Snow, water and light-colored sand reflect UV light too, increasing your exposure.