There are two kinds of sunscreens on the market: Chemical and Physical.
Chemical sunscreens that contain active ingredients such as Avobenzone, Oxybenzone, Benzophenone, which are absorbed into the skin. This is an undesirable consequence since the chemicals pass through the skin creating free radicals. These ingredients are known to irritate the skin and migrate (gets in eyes).
Physical agents, such as Zinc Oxide or Titanium Dioxide, act as an umbrella or metal blanket to reflect and scatter solar rays. Physical agents lay on top of the skin and are not absorbed, avoiding irritation.