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UVA vs UVB: The Different Types of UV Rays, How They Affect Your Skin and How to Protect From Both Year-Round

Is your sunscreen truly broad-spectrum?

We all know that the sun does damage to our skin—but the exact form and extent depends on which UV rays we’re exposed to. There are actually two different types of UV light that reach the Earth and affect us: UVA and UVB.

One is primarily responsible for sunburns, while the other is a trigger for skin cancers and premature aging. Sunscreens are supposed to protect us from both (that’s why they’re called “broad-spectrum”), but they don’t always do a good job. In fact, a recent investigation revealed that US sunscreens are inadequate against the most prevalent and dangerous form of UV.[1]

Shocked? Me too—which is why I created this tutorial. You will learn the difference between UVA and UVB, which one is the most harmful, and the best way to protect your skin year-round.

What Is the Difference Between UVA and UVB?

What Is UVA?

When you think of UVA, think “A” for aging. Ultraviolet A (UVA) radiation is chiefly responsible for aging your skin and triggering skin cancers. 

This is because UVA rays have the longest wavelengths, and penetrate the most deeply—all the way into the dermis, the middle layer of skin, where they cause cellular and DNA damage.[3]

“UVA rays are the longer-wave rays that do the most harm,” confirms Dr. Sharyn Laughlin, dermatologist and co-founder of The Sunscreen Company. “According to studies from the past two decades, UVA is the main driver of skin cancer and photoaging.”

When your skin is exposed to UVA, it causes an immediate tanning effect (which is why it’s the type of UV used in tanning beds). However, at the same time, it initiates other, more insidious changes—like suppressing your immune system,[4] generating free radicals,[5] and interfering with your body’s DNA repair processes.[6] 

This encourages the eventual formation of wrinkles and pigmentation, as well as melanoma and other skin cancers. You just can’t feel or see the damage right away—which is why UVA is often dubbed “the silent killer.”

What Is UVB?

When you think of UVB, think “B” for burning. Ultraviolet B (UVB) is a higher-energy, shorter-wave radiation that is directly responsible for triggering sunburns.

“UVB rays are the shorter wave rays in the UV spectrum, and are Nature’s warning signal to tell people to get out of the sun,” says Dr. Laughlin. “They penetrate to the epidermis [the outermost layer of skin], and initiate early sunburn.”

Anytime a sunburn occurs, your DNA gets damaged. Fortunately, if you get out of the sun right away, your body is capable of repairing it without consequences like aging and skin cancer.[7]

But if you stay in the sun—continuing to expose your skin to not only UVB but also UVA—then the UVA will make things worse. “If the individual remains in the sun and receives ongoing exposure to UVA, the DNA damage continues and is more severe: 94% of the mutations of skin cancer are UVA-induced, whereas only 6% are UVB-induced,” explains Dr. Laughlin.

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From The Skincare Edit Archives

In other words, UVB is the main culprit behind sunburns, but in combination with UVA can also trigger DNA changes that play a role in skin cancers.

Is UVA or UVB Worse?

When Is the UV Index the Highest?

Should You Wear Sunscreen Every Day, All Year?

Why Most Sunscreens Don’t Block UVA

In the sunscreen industry, there are several on-skin and computer tests that manufacturers use to calculate measurements such as the Sun Protection Factor (SPF), Critical Wavelength and UVA Protection Factor (UVAPF). According to Dr. Laughlin, a truly broad-spectrum sunscreen needs to be SPF 30 or higher, with a UVAPF of at least 10-20.

The problem is, the FDA and Health Canada don’t require UVAPF testing—even though it is the best way to determine how well a sunscreen defends against UVA. Instead, they allow manufacturers to infer the level of UVA protection (and therefore make the claim “broad-spectrum”) based on another, less accurate test.

“The word ‘broad-spectrum’ as it appears on North American labels is inaccurate: 90% of available sunscreens use 3% avobenzone, or zinc oxide at less than a 14% concentration, and can only achieve a UVAPF of 5-8,” explains Dr. Laughlin. “This has been proven by a computer model developed over the past 20 years, and further confirmed by the gold standard of testing on skin (in-vivo). In North America, UVA is inferred from a method called Critical Wavelength, which can be very misleading. Two sunscreens with the same Critical Wavelength may have widely different UVAPF values.”

So it’s not surprising that a recent study found the majority of sunscreens provided significantly lower UVA protection than implied by the imprecise term “broad-spectrum.” In fact, the average unweighted UVAPF values were just 24% of the labelled SPF. That means the typical SPF 30 might have a UVAPF of only 7, instead the 10-20 that is needed.[1]

How to Find a Sunscreen That Is Truly Broad-Spectrum

Since brands aren’t required to perform the UVAPF test or publicize their results, we can’t rely on that. Instead, these are the two key things to look for:

  • At least 15% zinc oxide: Here in North America, zinc oxide is the only available filter that offers extensive protection against both UVA and UVB.[11] Your sunscreen should have a minimum 15% concentration up to the maximum of 25%. 
  • SPF 30 or higher: SPF is a measure of how well a sunscreen guards against UVB. Rather than relying on the number claimed by the brand (which is often inaccurate[1]), you can estimate it yourself. According to industry sunscreen simulation tools,[12][13] every 1% of zinc oxide is equivalent to 1.6 SPF units. So a 20% zinc oxide sunscreen would be about SPF 32. Often, you’ll see zinc oxide in combination with titanium dioxide. Since every 1% of titanium dioxide is equivalent to 2.6 SPF units, a sunscreen with 15% zinc oxide and 5% titanium dioxide would be about SPF 35.

⚠️ Outside of North America, zinc oxide isn’t your only option. Tinosorb M, Tinosorb S and Tinosorb A2B are also effective against UVA. (In the US, none of the Tinosorb filters are approved, and in Canada, Tinosorb M and Tinosorb S are only allowed in low quantities.)

The Best Broad-Spectrum Sunscreens to Protect From UVA and UVB

These are just a few of my top sunscreen picks for guarding against both types of UV rays. For more recommendations, see my mineral sunscreen guide, tinted sunscreen guide and body sunscreen guide.

EleVen by Venus Williams Unrivaled Sun Serum SPF 35
Kinship Self Reflect Probiotic Moisturizing Sunscreen Zinc Oxide SPF 32
Pipette Mineral Sunscreen SPF 50
REN Clean Skincare Clean Screen Mineral SPF 30 Mattifying Face Sunscreen
Ghost Democracy Invisible Lightweight Daily Sunscreen SPF 33
CyberDerm Simply Zinc Lite Untinted Transparent Sunscreen Lotion SPF 50
HAN Serum CC with SPF 30

Conclusion + Further Reading

Now you know the difference between UVA and UVB, and the best way to protect your skin from their damaging effects. It all comes down to wearing a broad-spectrum sunscreen with strong UVA protection every day.

“The most important reason to use a sunscreen with high UVA protection is to prevent skin cancer over your lifetime, but I find that people are sometimes more motivated by preserving the look of their skin than statistics relating to skin cancer,” says Dr. Laughlin. 

“In my clinic, patients sometimes invest thousands of dollars into improving their skin with laser treatments and injectables, but I always tell them their investment goes out the window if they do not preserve it with a high-UVA sunscreen. Studies have shown that the daily use of a truly broad-spectrum sunscreen over a lifetime can shave up to 20 years off the look of your skin.”

Did you hear that? Wearing the right sunscreen can turn back the clock two decades! I don’t know about you, but hearing that statistic makes me extra-motivated to be diligent about UV protection, no matter what.

Further Reading

  1. Andrews, David Q., Rauhe, Kali, Burns, Carla, Spilman, Emily, Temkin, Alexis M., Perrone-Gray, Sean, Naidenko, Olga V. & Leiba, Nneka. (2022). Laboratory testing of sunscreens on the US market finds lower in vitro SPF values than on labels and even less UVA protection. Photodermatology, Photoimmunology & Photomedicine. 2022 May; 38(3): 224-232.
  2. Radiation: Ultraviolet (UV) radiation. (2016, March 9). World Health Organization.
  3. D’Orazio, John, Jarrett, Stuart, Amaro-Ortiz, Alexandra & Scott, Timothy. (2013). UV Radiation and the Skin. International Journal of Molecular Sciences. 2013 Jun; 14(6): 12222–12248.
  4. Kripke, M. L. (1979). Effects of UV radiation on the immune system: consequences for UV carcinogenesis. Advances in Experimental Medicine and Biology. 1979; 121(A): 589-98.
  5. Tyrrell, R. M. (1995). Ultraviolet radiation and free radical damage to skin. Biochemical Society Symposium. 1995; 61:47-53.
  6. Cleaver, James E. & Crowley, Eileen. (2002). UV damage, DNA repair and skin carcinogenesis. Frontiers in Bioscience. 2002 Apr 1; 7:d1024-43.
  7. Brash, D. E., Ziegler, A., Jonason, A. S., Simon, J. A., Kunala, S. & Leffell, D. J. (1996). Sunlight and sunburn in human skin cancer: p53, apoptosis, and tumor promotion. The Journal of Investigative Dermatology. 1996 Apr; 1(2): 136-42.
  8. Health Effects of UV Radiation. (2022, January 4). United States Environmental Protection Agency.
  9. Lister, Roberta. (2019, June 30). This is Why You Burn so Easily – Even When Slathered in Sunscreen. Women’s Health.
  10. Watts, Gemma. (2020, September 23). We Asked a Dermatologist to Bust Some Sunscreen Myths. Glow Journal.
  11. Sabzevari, Nina, Qiblawi, Sultan, Norton, Scott A. & Fivenson, David. (2021). Sunscreens: UV filters to protect us: Part 1: Changing regulations and choices for optimal sun protection. International Journal of Women’s Dermatology. 2021 Jan; 7(1): 28–44.
  12. BASF Sunscreen Simulator.
  13. DSM Sunscreen Optimizer.

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