This Is What SPF Really Means

Sunscreen should be an essential part of your daily skin care routine, especially during the summer months. It's also just as important to choose a sunscreen with an SPF that will adequately protect your skin from sun damage. But what does SPF even mean — and how much do you actually need?

SPF stands for sun protection factor. It measures how well a sunscreen will protect your skin from the sun's ultraviolet rays (via Hello Giggles). The sun emits two types of ultraviolet radiation: UVA and UVB rays, both of which can damage your skin cells. UVA rays cause skin damage that contributes to tanning and aging, while UVB rays are responsible for sunburn and skin cancer.

Although both ultraviolet rays can cause damage to your cells, SPF really just tells you how much UVB protection you'll be getting. That's why it's crucial to look for a sunscreen that provides both UVA and UVB protection. Products that provide this dual protection will most likely be labeled as "broad spectrum" sunscreen.

How much SPF do you need?

SPF 15, 30, 50 — what do these numbers even mean? "The factor indicates how many times longer your skin would be protected from burning compared to wearing no sunscreen at all," dermatologist Hiva Fassihi explained to Popsugar. For example, SPF 15 sunscreen will prevent you from UVB rays some 15 times longer than no sunscreen, while using SPF 50 sunscreen should take your skin 50 times longer to burn.

"If the SPF is factor 30 and you usually burn five minutes after exposure to the sun without protection, you can stay 30 times longer in the sun without getting a sunburn, that means a total of 150 minutes," Dr Marco Lens, a London-based plastic and reconstructive surgeon, told Popsugar.

However, the effectiveness of SPF doesn't really depend on the number as much as how often you apply it. While it's a good rule of thumb to use sunscreen with an SPF of 30 or higher, how frequently you apply it will determine how well your skin is protected against the sun's rays. Although you should initially apply a generous amount of sunscreen 20 minutes before going outside, you should reapply the same amount every two hours.