Sunscreens get their efficiency from the solar filters present in the formula.
There are two types of filters:
Organic filters: ingredients that penetrate the skin and absorb the energy from the sunbeams, so they do not penetrate to the deeper skin layers and cause damage. Organic filters are absorbed like a normal body lotion. These filters are also called chemical filters.
Inorganic filters: Usually titanium dioxide, but there are also other kinds of inorganic filters. Inorganic filters reflect the rays, like a mirror, preventing them from penetrating the skin. These filters are sometimes also called physical filters, since they are not absorbed by the skin, but form a layer on top of the skin, often making the skin white.