According to the Skin Cancer Foundation, a good SPF number depends on expected sun exposure, skin tone, age and family history of skin cancers. An SPF of 15 is generally sufficient for daily activities. For extended sun exposure, an SPF of 30 or higher is recommended.
SPF stands for sun protection factor. The higher the SPF, the more ultraviolet radiation the sunscreen filters out. All sunscreen used should have broad-spectrum protection, which means that it effectively protects against the ultraviolet A and B ranges. SPF 15 filters out 93 percent of UV radiation, SPF 30 filters out 97 percent and SPF 50 filters out up to 98 percent.