“Importanltly, it can reduce the incidence of skin cancer by about 50 percent.”Do I need to put it on every day? Numerous studies confirm that daily sunscreen use–even during the winter and when indoors–does reduce the risk of skin cancer. It’s important to wear sunscreen on any day where the UV index is over 2. According to MD Anderson Cancer Center, UVA rays make up 95 percent of all of the UV rays that get to Earth’s surface. While UVB rays only make up the other five percent of UV rays, they are very high energy.