What does an SPF of 30 indicate?

An SPF of 30 indicates that it blocks approximately 97% of UVB rays, which are the primary cause of sunburn and contribute to skin cancer. This percentage is crucial for determining the effectiveness of sunscreen; a higher SPF generally provides more protection, but the differences in percentage become smaller as SPF increases. For example, while SPF 15 blocks about 93% of UVB rays, SPF 30 offers a bit more coverage without a dramatic increase in the percentage blocked.

The other options either misrepresent what SPF signifies or pertain to other unrelated factors. For instance, the claim about being suitable only for oily skin is inaccurate, as SPF formulations cater to various skin types. The statement regarding reapplication every hour is misleading; while it is important to reapply sunscreen, this guidance applies irrespective of SPF level, usually after swimming or sweating. Lastly, saying it provides full sun protection misrepresents the concept of SPF, as no sunscreen can block 100% of UV rays.