Demystifying SPF: What Is It, How Much Do You Need and Is Higher Really Better?

Get the sun protection you need like a pro.


Demystifying SPF


When you hear that one in five people will develop skin cancer in their lifetimes, that might send you running to the sunscreen aisle. As you stare at a wall of choices in various tubes, tubs, sticks and gels, confusion might set in. Which should I choose? How much protection do I really need?

To help you sort through your choices and get the sun protection you need like a pro, we’re breaking down UV rays and how they relate to SPF — what it is, how much you need and what those numbers really mean. You’ll be on your way to a smarter sun routine in no time.

What are UV rays?

There are two types of UV (ultraviolet) rays that can have an effect on your skin: UVA and UVB.

UVA rays are associated with aging, tanning and wrinkles.

UVB rays are associated with sunburns, eye damage and skin cancer.

UVA rays make up about 95 percent of the radiation from the sun. UVB rays make up the rest. Even though UVB rays are the lowest percentage of UV rays to actually touch your skin, they are the most harmful and have everything to do with SPF.

What is SPF and what does the number mean?

SPF (sun protection factor) is a measure of protection from UVB rays. Let’s break down SPF numbers and what they really mean.

Contrary to popular myths, an SPF number isn’t a measure of time of how long a product will protect you from the sun. A product with an SPF 30 means you can stay in the sun 30 times longer before you begin to burn than if you weren’t wearing sunscreen. For example, if you'd usually burn in 10 minutes, an SPF 30 would hypothetically allow you to stay in the sun for 30 times longer without burning, or 300 minutes.

But it's not that simple. That 300 minutes comes with caveats, like proper reapplication. To get the maximum benefit out of any sunscreen, you should apply every two hours or immediately after heavy exertion (sweating) or swimming.

Should I go for the highest number SPF?

You want a product with a high SPF so you can stay in the sun longer, right? Not really. A high SPF sunscreen lasts just as long as a low SFP sunscreen. You still need to reapply both products every two hours. That SPF number also has to do with the percent of UVB rays the product blocks.

Here’s how protection breaks down by SPF number:

Percentage of UVB rays blocked

  • SPF 15: 93 percent
  • SPF 30: 97 percent
  • SPF 50: 98 percent
  • SPF 100: 99 percent

Source: EWG

The American Academy of Dermatology recommends using a water-resistant, broad-spectrum sunscreen with an SPF 30+. But what's a broad-spectrum sunscreen? Great question.

If a sunscreen isn't broad-spectrum, it can have a high SPF and still not protect you from all the sun's rays. Since SPF numbers only address UVB protection, broad-spectrum sunscreens offer equal protection against both UVA and UVB rays. This is an FDA (Food and Drug Administration) rating and can’t be claimed by every product.

How can I get the most benefit out of the SPF I choose?

Another great question. No matter the level of SPF you choose to wear, here are some tips to help you get the maximum protection from any product.

  • Application: Apply your sunscreen 30 minutes before going outside. Reapply every two hours. Reapply sooner if you have gone swimming or broken into a sweat.
  • Apply the proper amount: Most people under-apply sunscreen (sprays are the easiest to under-apply). Use one ounce (a shot glass full) to cover your entire body.
  • Don’t forget your lips, tips and tops: Use an SPF lip balm to protect your pucker and don’t forget the top of the head and feet as well as the tips of your ears.
  • Mind the water and snow: Both water and snow can magnify the sun's rays and cause damage faster. Be sure to reapply sunscreen more frequently when you're close to water or partaking in winter fun.
  • Hit the shade: Take a break from the sun and be sure to hit the shade, summer and winter. Your skin deserves a break, no matter the time of year.
  • Don’t forget clothes: Clothing offers additional SPF protection. A wide-brimmed hat, sunglasses and even a lightweight, long-sleeved shirt or pants can boost your SPF protection. You can also look for active fabrics with built-in SPF ratings.


Now, you’re an SPF pro and can navigate that sunscreen aisle with confidence. Don’t forget that applying sunscreen isn’t a one-and-done for the average day. You’ll get the most protection from consistent reapplication and taking additional protective measures like shade and clothing.


E. Napoletano is an award-winning journalist and author and the recipient of the 2019 Illinois Women’s Press Association first-place prize for her feature on the traumatic effects of family separation policies at the border.