The difference between sunblock and sunscreen is often misunderstood. Sunblock and sunscreen are considered to be synonymous terms, which is not the case. As the names imply, one blocks the sun’s rays and the other screens them. Sunscreens keep most rays out but let some in. Sunblocks physically reflect the sun’s rays from the skin.
There are chemical sunscreens and physical sunblocks. The sunblocks are generally made from more natural mineral ingredients. The FDA currently approves 17 ingredients for sun protection, some physical, and some chemical. Making an informed choice requires familiarity with the differences. To make it more confusing, some brands are blends of sunscreen and sunblock.
Chemical sunscreens absorb UVB rays. A common chemical used for this purpose is PABA: para-aminobenzoic acid. They are starting to more commonly contain UVA blocking ingredients also.
Physical sunblocks provide a physical barrier to ultraviolet radiation by reflecting that radiation away from the skin. They protect against UVB and UVA light. They are often made from titanium dioxide or zinc oxide and have an opaque color and thick consistency. This thickness does cause them to be hard to camouflage on the skin, often showing as a white, possibly streaky, residue visible on the skin. They wash off less easily than chemical sunscreens, which deter some from using them. They are the natural option though, and they are probably the best option for people with sensitive skin who may be allergic to the common ingredients in chemical sunscreens.
Either sunblock or sunscreen can be equally effective at protection from the harmful effects of sun exposure, as long as they have an SPF rating of at least 30.