The active ingredients in sunscreens absorb, reflect or scatter ultraviolet radiation, changing the body’s response. Sunscreens typically contain a combination of chemicals known to be effective for certain wavelengths of UV light. Some chemicals work better than others, as do some combinations of chemicals. For years, manufacturers created sunscreens that were only effective at screening out UVB radiation, which caused sunburn and increased the risk of skin cancer. More recently, scientists realized that UVA radiation is also harmful, so sunscreen manufacturers have attempted to create sunscreens that protect skin from both UVB and UVA radiation. All sunscreens provide UVB protection but vary widely in UVA protection. A sunscreen with UVA is important because these rays penetrate glass. So if you spend allot of time in the car commuting to work, that’s time spent aging your skin.
So when you see a sunscreen marked ‘broad spectrum’ it will essentially block both harmful rays.
But keep this in mind when shopping for a sunscreen. In order for a sunscreen to protect you from the suns rays it only needs to contain Zinc oxide. Zinc oxide is the ONLY active sunscreen ingredient. 90% of the sunscreens out there on the market contain other harmful chemicals that are coincidentally enough linked to causing cancer. So buyer beware!