How sunscreen works: Most sun protection products work by absorbing, reflecting, or scattering sunlight. They contain chemicals that interact with the skin to protect it from UV rays. All products do not have the same ingredients; if your skin reacts badly to one product, try another one or call a doctor.
SPF: Sunscreens are assigned a sun protection factor (SPF) number that rates them in blocking UV rays. Higher numbers indicate more protection. You should use a sunscreen with at least SPF 15. Sunscreens labeled with SPFs as high as 100 are now available.