Sunscreen and sunblock are both excellent forms of sun protection. Each uses different chemicals to protect the skin against the sun's damaging UV rays. Most sunblocks utilize titanium oxide or zinc oxide as the active ingredient, which results in a thicker, opaque consistency. Some consider this to be a disadvantage because the consistency makes it difficult to spread all over the body. Secondly, many sunblocks are opaque and can be seen on the skin after application. You may notice people wearing sunblock, especially at the beach, with streak of sunblock on their noses and other parts of their face. There are some brands, like Neutrogena, that offer a less visible sunblock.
Sunscreens use a variety of chemicals that work to absorb harmful UV rays before they penetrate your skin. Some people are sensitive or allergic to certain ingredients, like PABA, and choose to use sunblock instead of sunscreen. In fact, many brands today are a blend of sunscreen and sunblock, so its important to check the label if you have a sensitivity to certain chemicals.
Both sunscreen and sunblock provide protection against the sun. Choosing between the two is a matter of personal preference and necessity. As long as you choose an SPF of at least 30, the current recommendation from the American Academy of Dermatologists, you are providing adequate protection for your skin.