There are two types of sunscreens: Chemical and physical.
Physical (mineral) sunscreens are made with minerals (titanium dioxide and zinc oxide) that form a natural, protective layer on the skin that blocks the sun's harmful rays. Chemical sunscreens (Avobenzone,Octinoxate,Octisalate,Oxybenzone ,Mexoryl SX and Tinosorb) absorb UV rays.
Chemical sunscreen ingredients offer the best protection, especially against cancer- and age-causing UVA rays they offer more coverage against UVA and UVB rays than physical sunscreens. Avobenzone, for example, protects against the full spectrum UVA rays. Although chemical sunscreens can cause free radicals which can make your skin age, so always layer an antioxidant underneath your sunscreen.
Chemical sunscreens contain UV filtering ingredients that take time to be absorbed by the skin - hence people using the 20 minute rule before sun exposure. Chemical filters also tend to be more irritating to the skin and can cause allergies, either when applied or when exposed to the sun. But some sunscreens now use Mexoryl since it has less chance of irritation. They also apply well into the skin and are often colourless & odourless.
Physical (mineral) sunscreen ingredients such as zinc oxide and titanium dioxide are another option. These protect your skin from the sun by deflecting or blocking the sun's rays, they form form a protective barrier on top of the skin, and these have an immediate effect. They are a great option for those who have frequent allergies, children under 5 or anyone who wants to avoid chemicals. Zinc is also anti-inflammatory and does not block pores. Physical (mineral) sunscreens tend to be better tolerated by most skin types because the chemical filters used in chemical sunscreens can be irritating for many people. However, Titanium dioxide can be problematic for some people. Physical (mineral) sunscreens are also a bit thicker so they may be more difficult to apply and don’t offer as much UVA protection compared to chemical sunscreens. However some argue that with physcal (mineral) sunscreens it creates a barrier between the skin and the sun, therfore they are more effective than chemical filters at blocking UVA and UVB. Also many of the newer physical (mineral) sunscreens coming out on the market are much more refined and cometically elegant.
Since they each have their pros and cons, many of today's sunscreens contain both physical and chemical UV filters.