Protecting both UVA + UVB
Broad spectrum protection refers to protection from both UVA and UVB waves. Originally, sunscreens were designed to protect against UVB rays, which cause sunburn but only account for a small portion of the full UV spectrum. UVB rays were once thought to be the only rays that could cause harm and UVA rays were thought to produce a "healthy" tan. We now know that UVA rays contribute to premature skin aging and some forms of skin cancer.