> People can develop third-degree burns from the sun. The reason we have seen such a rise in cancers over the past 30 years is because it has coincided with a boom in international travel.
Apart from the dangers of skin cancer, there's the risk of renal failure. If you get lots of weeping blisters you will lose fluid, and you may be dehydrated anyway, so the situation gets worse.
Sunstroke, can ruin your holiday. You will have to contend with nausea and headaches.
You need to limit exposure. There's a reason why in most very hot countries people spend the peak of the day indoors -- it's only us that have this tendency to lie in the baking sun. Just because it's overcast doesn't mean there's no UV. In fact there is added danger, because the temperature will be lower so people don't tend to realise how exposed they are.
Water can also be dangerous, because it superficially cools things down. If you are lying by a pool, dipping in and out, you may not overheat, but it won't stop you from burning.