Sunblocks physically prevent sunlight from reaching the skin, mainly by reflecting it.
They are usually a cream containing a metal such as zinc oxide or titanium dioxide. They are rarely used for whole body protection, being kept for regions of high exposure such as the nose. Others may also contain esthers of cinnamate. The higher this number, the greater the power to block ultraviolet radiation. In theory, a person can spend longer in the sun with a sunscreen of a higher SPF rating.