By SPF

SPF works by extending your skin’s natural defenses against the sun’s rays. For example, an SPF of 15 provides about 15 times more protection than just your normal skin without sunscreen. An SPF of 50, then, would provide 50 times more protection than skin without sunscreen. Choosing a broad-spectrum sunscreen means it’s a type of sunscreen that will block out both UVA and UVB rays.