Is there a difference between sunscreen and sunblock?

No: They both provide protection to skin from the harmful sun rays(uv light).

Different mechanisms: Sunscreen decreases the effects from uv b but not uv a which leads to photo aging like wrinkles. A sunblock will have zinc or titanium oxide crystals to "block" the sun.

None: Both do the same thing in blocking out rays of sun.

Sunscreen/sunblock: The difference between is how good they are at screening out harmful radiation from the sun. Blocks are stronger and thus more effective at keeping out those harmful UV rays. Blocks are also usually more visible. For instance, the white zinc oxide life guards use on their nose is more of a block. Nothing is 100% though, so hats with wide brims and lightweight clothing works well too!