In New Zealand and Australia, most people who have European origins and especially those who freckle and burn easily will have suffered significant damage to their exposed skin. This generally means that the face will be sun damaged and this applies predominately to the nose, cheeks and forehead. Lips are very vulnerable to sun damage and it is not uncommon for me to remove all the lower lip skin due to skin cancers forming there.
The best protection from the sun is to cover your skin whenever you are exposed to the sun. You can cover your skin either by using a hat, shirt or trousers but you can also cover your skin by using sunscreen. The ingredients in sunscreens that act like a physical barrier are Titanium oxide and Zinc Oxide, both of which are inorganic chemicals. Because they cause your skin to be white so some manufacturers create nano-particles of these chemicals making the white colour not as obvious. Some sunscreens will also have a colour tint to mask the whiteness of these chemicals. These chemicals are very effective in blocking UV radiation and therefore reducing damage to the skin.
The other chemicals that are included in sunscreens are the organic chemicals that are combined with the inorganic chemicals mentioned above. The combination has synergies, which means that they are both more effective when combined with each other.
If there is significant damage to facial skin then my recommendation to my patients is that they apply a broad spectrum SPF 50+ sunscreen on their face every day of their lives. UV rays penetrate cloud layers so it is a myth to think that sun damage does not occur in the winter. Because we are creatures of habit creating the habit of applying sunscreen after cleaning ones teeth every morning means you are "putting money in the bank of protection." The minimum SPF should be 30+ if you are serious about optimising protection from the sun.
Some people worry about using chemicals on their skin because of the possibility of free radicals forming as a result of their breakdown. There are plenty of theories about this however I am not aware of any science to back up those claims. There is a mountain of evidence that clearly shows the benefit of using sunscreens for those who need it.
You will pay more for brand name sunscreens, also for sunscreens that contain nano-particles and for those that have a nicer cream base. Find one that suits your purse and your skin.