There are two general types of sunscreens, physical and chemical. Physical sunscreens use physical UV filters, while chemical sunscreens use chemical UV filters. Both physical and chemical sunscreens will do a great job at protecting your skin from UVA and UVB rays, as long as you apply them correctly every morning and reapplying throughout the day.
PHYSICAL SUNSCREENS contain active mineral ingredients, such as titanium dioxide or zinc oxide, which work by sitting on top of the skin to deflect and scatter damaging UV rays away from the skin. Titanium dioxide protects against UVB rays, but not the full spectrum of UVA rays. Zinc oxide protects against the entire spectrum of UVB and UVA rays.
CHEMICAL SUNSCREENS contain organic (carbon-based) compounds. These compounds create a chemical reaction and work by changing UV rays into heat, then releasing that heat from the skin. Must apply directly on skin!