Include sunscreen as a part of your skin care routine, when spending time outdoors. Most skin cancers are preventable by limiting time spent in the sun, using protective shade, clothing and correct sun protection. Sun rays also have an aging effect on skin. Sunscreens contain either chemical filters, which absorb the rays preventing them from entering the skin, or physical filters, which directly block the rays. The effect of a sunscreen is defined by the Sun Protection Factor, SPF. It is recommended to use a sunscreen with an SPF of 15 or 30 as sun protection.