There are two different types of sunscreen: chemical and physical. Chemical sunscreens often contain active ingredients like Octylcrylene, Avobenzone, Octinoxate, Octisalate and Oxybenzone. They work to absorb UV rays and are usually colourless and odorless, making them ideal for adding into foundations and makeup primers.
Physical sunscreen contains actives like zinc oxide and titanium dioxide, which reflects and blocks UV rays. They are often responsible for leaving a white cast after application.