Derma recommends that you:

• Keep track of the UV index in your area
  If you have light skin without any sun screen protection, you could get a sunburn in about 15 minutes! Wherever you are  located geographically, in the south the UV index can be very high most of the day, not just between the hours of 12 and 15 like in the North. If the UV index in your location is above 7, you should use a sun screen with a higher SPF number - or stay in the shade. Follow the sun protection recommendations from the Cancer Society in your country.
   
• Apply ample amounts of sun screen
  About half an hour to an hour before you go out into the sun and again just before you leave. It is not certain that your body can absorb 40 ml (recommended for adults) in one application. Studies show that it is optimal to apply sun screen twice before you go out in the sun for the entire layer of sun screen becomes thicker, and without missing any spots. And always apply a new layer after going in the water and when perspiring.
   
• Using the right UV sun protection factor (SPF)
  In the Nordic countries, SPF 15 is usually enough for people with normal skin type. If you have extra light or sensitive skin, you should use a higher UV protection factor. This applies to both children and adults. In countries close to the equator, where the UV index can be very high, use a sun screen with a high protection factor, i.e. SPF 30 or higher.

Follow the sun protection recommendations from the Cancer Society in your country.