Sunscreens come in two general types, chemical and physical. Chemical sunscreens are effective, but some people are allergic to the ingredients. If you opt for a chemical sunscreen look for one that contains Avobenzone or Mexoryl.
I prefer physical sunscreens that contain zinc oxide and titanium dioxide. They block more of the spectrum and have less potential to cause an allergic reaction. For people with rosacea or sensitive skin/eczema, physical sunscreens have an added benefit, zinc oxide soothes irritation (think diaper rash ointment). There are many excellent physical sunscreens on the market and most moisturizers now have a good degree of sun protection. Remember to look for moisturizers with SPF of at least 30, even if you're going to be sitting in an office all day-UVA rays penetrate glass!