Question: what is the difference between factor 20 and 30?
Answer: What's the difference between SPF 30 and 50? ... SPF 30 is the most common level for most people and skin types. No sunscreen can block all UV rays, but what we do know is: SPF 15 blocks 93% of UVB rays, SPF 30 blocks 97% of UVB rays and SPF 50 blocks 98% of UVB rays.