A Guide to SPF: What Does SPF Stand For and What Does it Mean?

Posted August 22, 2018

Is there anything that screams “summertime” quite like the smell of sunscreen? It immediately transports you back to your childhood—carefree days spent at summer camp, splashing around in the pool, and hanging out with friends.

Through all your years, sunscreen has been there for you, to protect your skin, keep you safe from UV radiation, and prevent signs of aging. But despite our familiarity with sunscreen, one thing still remains a mystery for many: what in the world is SPF?

If you’re like most people, you’ve lived your life by one rule: the more SPF, the better. But is that really true? What does SPF even mean? How does it work? Today, we’re going to answer those questions for you—and so much more. Let’s demystify SPF.

What is Sunscreen?

Before we can dive into the particulars of SPF, the first step is understanding the basics of sunscreen. The sun omits two types of UV rays that are particularly harmful to your skin: UVA and UVB rays. UVA rays penetrate deep into the skin, causing long-term damage like aging and wrinkles. UVB rays, on the other hand, are shorter than UVA rays. They burn the surface of your skin, causing immediate damage like sunburns and skin cancer in the long run. Sunscreen is designed to protect your skin from the sun’s damaging rays. It does so in a variety of ways, including absorbing and deactivating, degrading, and reflecting the rays.

What is SPF?

Despite the fact that very few people know what it is, SPF is actually pretty straightforward. SPF stands for “Sun Protection Factor”, and is a measure of the sunscreen’s ability to protect your skin from UVB rays. The basic calculation works like this: “If it takes 1 minute for your unprotected skin to start turning red [in the sun], using an SPF 15 sunscreen theoretically prevents reddening 15 times longer.”

Say you purchase an SPF 30 sunscreen. If it typically takes 10 minutes until your skin starts to burn, by using the SPF 30, you’re theoretically protected from the sun for 300 minutes, or 5 hours.

what-is-spf

It’s important to remember that SPF only protects against UVB rays; those are the rays that are causing the “reddening”, or surface burns. SPF doesn’t account for UVA rays; those are the rays that cause long-term damage including aging and wrinkles.

UVA rays can do a lot of damage before your skin turns red. In fact, 1 in 5 Americans will develop skin cancer by the age of 70—and many of those due to the damaging effects of UVA rays.

what-is-spf

What Amount of SPF is the Right Amount?

As a general rule, less than 15 SPF is considered mild protection, SPF 15-30 is considered moderate protection, and higher than 30 SPF is considered high protection. An average person is safe using an SPF 30 sunscreen, as long as they’re applying enough and reapplying frequently—but it’s not a one-size-fits-all rule. Determining the right sunscreen for you depends on your skin. “SPF 15 filters out approximately 93 percent of all incoming UVB rays. SPF 30 keeps out 97 percent and SPF 50 keeps out 98 percent. They may seem like negligible differences, but if you are light sensitive, or have a history of skin cancer, those extra percentages will make a difference.”

what-is-spf

The common assumption about SPF is that more SPF means more protection against the sun. If applied exactly as directed in a controlled setting, such as a laboratory with a fair climate, a stable amount of UVB exposure, and no other external factors to affect its performance, this is true. But it’s fairly unlikely that you’re applying enough and it’s extremely unlikely that you’ll ever been in an environment of the sort. Furthermore, things like sweating and swimming lessen the efficacy of SPF. Most experts warn that no sunscreen can be realistically expected to work for longer than 2 hours.

What is Broad Spectrum Sunscreen?

As we mentioned, SPF really only refers to protection against UVB rays—but those aren’t the only rays that may be doing you harm. UVA rays cause long-term damage like aging and wrinkles, and can do a lot of harm before your skin burns. The fact of the matter is that protection against only UVB rays just isn’t enough. That’s where broad spectrum sunscreen comes in.

Broad spectrum sunscreen (also known as full spectrum sunscreen) protects against both UVA and UVB rays. And, frankly, it’s a must. In order for a sunscreen to be considered “broad spectrum”, its UVA protection must be proportionate to its UVB protection. As SPF and therefore UVB protection increases, as must UVA protection.

How Should I Apply Sunscreen?

Remember when we said that sunscreens only provide the labeled level of SPF when applied “exactly as directed”? Let’s talk more about what that means.

The first thing to remember when applying your sunscreen is that you’re probably not applying enough. Experts estimate that most people only apply between 25% and 50% of the recommended amount. SPF tests are based on the presence of 2 milligrams of sunscreen for each square centimeter of skin’s surface.

what-is-spf

In simpler terms, that equates to roughly a quarter sized dollop for your face and a shot glass worth for your body. Be sure to get very exposed areas, including your neck, ears, nose, lips, and the tops of your feet.If your sunscreen is aerosol, that measurement isn’t quite as simple. Aerosol sunscreen is much harder to control, as breezy environments and improper application can leave your skin susceptible.

Reapply, Reapply, Reapply

Here’s the thing about applying sunscreen: just doing it once simply isn’t enough. Reapply your sunscreen every 90 minutes. If you’ve been doing a lot of physical activity, sweating, swimming, or towel drying yourself, reapply sunscreen immediately.

Remember that sunscreen isn’t only a must on sunny days. Whether sunny or cloud, rain or shine, sunscreen is a vital part of your daily routine.

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