The sun protection factor (SPF) tells you how effectively a sunscreen protects against UVB radiation. A sunscreen with SPF 10 means that the length of time you can stay in the sun without burning is ten times longer than it would be without protection. Sunburn is mainly caused by the short-wave UVB radiation. Sunscreens help to shield against this radiation. However, a product with a very high SPF does not provide that much more protection against radiation. A product with SPF 10 already blocks 90 percent of the UVB radiation, one with SPF 20 blocks about 95 percent. Sunscreens with higher SPFs only provide minimally more UVB protection. So lotions with SPF 20 or 30 give sufficient protection even for small children, provided that parents follow the recommended guidelines to prevent over-exposure to the sun.
