What are the differences between sun block and sunscreen?

Sunscreen / Block. Sunscreens work via 2 possible ways: 1) chemical blocks that breakdown the uv rays as they pass through the skin and 2) physical blocks that prevent the uv rays from getting to the skin. I recommend the physical blocks (zinc and titanium) because they have a very good safety profile and work very effectively. If you are going to be in the sun - use a minimum of spf 15 - follow product directions.
The same. Basically, you wish a sun screen, as the term block is not used. Look for a mechanical block with micronized Zinc & Titanium. These are mechanical blocks which prevent the sun from affecting the skin. No block is permanent. You need to reapply it, especially if you have been swimming. www.artofplasticsurgery.com.
Just marketing. The fda has recommended that the term sunblock be dropped as it is often very misleading and can result in patients believing they have more protection from the sun than they actually do. I agree, a good sunscreen with an spf of 50, that contains both a uvb protector and a metal such as zinc or titanium oxide for uva. That's all you need if you reapply it frequently.