Sunscreen is a chemical protection while sunblock is a physical protection. Sunblock physically blocks ultraviolet (UV) rays while sunscreen absorbs the rays.
Sunscreens and sunblocks are important in protecting the skin from harmful UVA and UVB rays. The SPF, or sun protection factor, denotes how effective a cream is at absorbing UV rays.
Sunblocks are always a thick, opaque cream containing ingredients such as titanium dioxide and zinc oxide. The physical protection blocks forms of UV rays including UVA and UVB. Sunblocks are often cosmetically unappealing as they are visible, difficult to wash off and messy. Sunblocks are recommended for people with an unusual sensitivity to UV rays. Sunblocks cannot be quantified by SPFs as they reflect the rays rather than absorbing them. The SPF of a sunblock is greater than 30.
Sunscreen is a cream which forms a thin, colorless film on the skin that acts as a filter against UV rays. Ingredients in a sunscreen filter reduce and absorb harmful UVA and UVB rays.
Both creams should be applied 30 minutes before sun exposure to ensure protection. Sunscreen or sunblock should be used if exposed to sunlight for longer than 20 minutes.