Are you protected from the sun’s rays in the shade? Not completely. Because the rays get reflected by sand, water and other objects, you can burn even when you're in the shade. And it's important to protect the skin even on cloudy days. Cloud cover reduces UV radiation, but not so much that you don't need sunblock.

Sunscreen can be described as water-resistant if it still offers at least 50 per cent protection after around half an hour in the water. You should therefore reapply your cream as soon as you’ve dried off.

The length of time you can stay in the sun depends mainly on your skin’s own natural sun protection. The fairer the skin, the less exposure it can tolerate. The sun protection factor (SPF) of the sunscreen multiplies the length of time you can go without burning. This doesn’t mean, however, that you can stay in the sun all day as long as you keep reapplying cream. 

This doesn’t increase the protection time; it merely restores it after the sunblock has been washed off or rubbed off by a towel.

Tanning in a solarium won’t increase your skin’s natural protection. Unlike natural sunlight, which contains both UVA and UVB radiation, many solariums only use UVA. UVA tans your skin but doesn’t protect it from further radiation. 

Tanning under UVB gives slight protection from further radiation but also damages the skin. From a medical standpoint, exposing your skin to additional UV light is not recommended.

Many people think that after a certain time sunburn turns into beautifully tanned skin. Strictly speaking, though, this isn’t the case, because sunburn is neither a preliminary phase nor the cause of tanning. It's actually an acute inflammatory reaction of the skin. In some cases the skin does indeed turn brown, but that’s because of the UV rays received while sunbathing. 

It’s much better for the skin if you go brown without getting sunburnt first. But the general rule of thumb is that any tanning is a sign of damage to the skin. So you can do your skin good if you occasionally skip the sunbathing.