Sun screen needs to be used every day on all sun expose areas. You should look for a sun screen with minimum SPS of 30 and it should be re applied every 1 to 2 hours when you are not indoors. There is a lot of controversy going on about safe sun screen ingredients and unfortunately I don't feel that we have enough strong data on either side to be totally firm about my recommendations for this but I do know 1 thing. I know that skin cancer kills people and they know that sun protection starting at early age is important for preventing people from dying from skin cancer. 5 sunburns in childhood doubles your risk of melanoma in your lifetime and one single blistering sunburn in childhood also doubles your risk of melanoma in your lifetime. I choose to take a very practical assault with my children and with my recommendations to the patients. One is I believe that people should cover up. You need to wear a long sleeve, hats, long pants when you are outdoors because when you are covered up you don't need to put as much sunscreen on your body. Therefore, you are getting less potential exposure to those may be okay or may be not okay chemicals. However, as far as sunscreens are concerned that's where it gets a little more difficult. I typically recommend to people that they put a base of mineral sunscreen of zinc or titanium but I find that young people are very resistant in re applying this during the day. For my children, I choose to reapply with a nice spray which you need to put on heavily so the skin is wet and with a stick on the face because for my own feeling is, is that I know the sun is harmful and I am not sure where stand about the different ingredients in sunscreen so I tried to maximize the safety as far as I am concern. My Mom's treat for sunscreen is more avid and more often.