Sunscreen contains active ingredients that absorb or reflect the sun’s ultraviolet (UV) rays. Sunscreens can be categorized based on their ingredients into two groups: physical and chemical sunscreens. Physical sunscreens, such as zinc oxide and titanium dioxide, protect your skin by using physical UV filters to block or deflect UV light. Physical sunscreens tend to be better tolerated by most skin types because they are not absorbed into the skin. Chemical sunscreens, such as oxybenzone, octinoxate, and avobenzone, protect the skin by first absorbing UV light, then transforming that light energy into some other form of energy, such as heat. A benefit of chemical sunscreens is their ability to defend the deeper layers of skin, including collagen fibers and other tissue, against the aging effects of UVA rays. 
In order for a sunscreen to be labeled as “broad spectrum”, the active ingredients must be able to protect the skin from both ultraviolet A (UVA) and ultraviolet B (UVB) rays. Lastly, sunscreens will have a Sun Protection Factor (SPF) on their label. SPF is defined by the FDA as “how well a sunscreen protects you from sunburn”. Thus, the number following SPF on a sunscreen label tells you how much UVB light that sunscreen can filter out. For example, SPF 15 can filter 93% of the sun’s UVB rays, whereas SPF 30 can filter 97%.