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.
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?
Before we get into the different types of UV, let’s go over what UV is in the first place.
UV stands for ultraviolet light or ultraviolet radiation, a form of invisible electromagnetic energy that comes from the sun. It can also be produced by man-made sources such as black lights and tanning beds (although you should definitely steer clear of the latter!).
UV rays are measured on a scale called the electromagnetic spectrum, which also includes visible light and infrared light. They’re classified according to wavelength (the distance between peaks in a series of waves). Low-energy radiation has longer wavelengths, while high-energy radiation has shorter wavelengths.
Sunlight produces three wavelengths of UV radiation:
- UVA is long-wave radiation between 315 and 400 nanometers (nm)
- UVB is short-wave radiation between 280 and 315 nm
- UVC is intensive short-wave radiation between 100 and 280 nm
Fortunately, we don’t need to worry about UVC, since it is filtered out by the ozone layer and never reaches the Earth’s surface.
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.
“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, generating free radicals, and interfering with your body’s DNA repair processes.
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.
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.
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?
So, which type of UV is worse: UVA or UVB? According to experts, it’s UVA rays that we should be the most worried about.
First of all, UVA is far more prevalent than UVB. It accounts for 90-95% of ambient sunlight, whereas UVB is only 5-10%.
We also know that up to 90% of the skin changes attributed to “aging” are in fact caused by the sun—and it’s clear that UVA is the main culprit.
“The most damaging rays from the sun are in fact in the UVA spectrum,” says Dr. Howard Murad, dermatologist and founder of Murad. “UVA rays are actually the same strength all year round and can even penetrate through clouds and windows. Plus, they can contribute to premature aging, collagen degradation and even skin cancer.”
When Is the UV Index the Highest?
Now you might be wondering about the safest time to get sun exposure.
The UV index is an international measurement system that predicts the level of UV radiation on any given day. It takes the following factors into account to estimate the strength of UV radiation reaching the Earth (and your skin):
- Time of day: UV rays are at their daily peak between 10 a.m. and 4 p.m. The time between noon and 1 p.m., known as “solar noon,” is when they are the most intense.
- Time of year: The spring and summer months are when UV is the strongest, because the sun is high in the sky and its rays shine down more directly.
- Latitude and altitude: The closer you are to the equator, the more UV exposure you get. The same goes for higher elevations—the higher up you are, the stronger the UV.
- Clouds and haze: Although UV rays can penetrate through thin clouds and haze, thick and heavy cloud cover can block most UV from getting through.
- Ozone: The ozone layer, which is continuously fluctuating, absorbs UV radiation, making it less intense once it reaches Earth.
- Reflection: UV light can bounce off surfaces such as snow, ice, sand, water and concrete.
The higher the UV index, the more precautions you’re meant to take:
- Low (0-2): The best time to be outside, with low risk of sunburn.
- Moderate (3-5): This calls for routine sun protection measures—like wearing SPF 30 and covering up unprotected skin.
- High (6-7): When UV exposure is high, it’s recommended to seek shade at midday in addition to wearing (and re-applying) sunscreen and sun-protective clothing.
- Very High (8-10): At these times, you’re at a very high risk of burning, and should consider avoiding the sun during peak hours.
- Extreme (11+): This means that unprotected skin (and eyes) can burn within just a few minutes, and sun exposure should be avoided altogether.
But should you rely on the UV index to determine when you need to apply sunscreen?
Probably not, says Dr. Cara McDonald, dermatologist and director of Complete Skin Specialists Dermatology. “It’s really a vehicle for public awareness. We don’t see much sunburn and we don’t see much increased risk of skin cancer if the UV index is below 3. However, we do still see some effects of UV light, particularly on our signs of aging. From my point of view, I don’t want to have to check the time of the day and where I am and whether or not the UV index has gone above 3. So, personally, I would just suggest that we wear [sunscreen] all the time, particularly in those areas that are frequently exposed, like the face.”
Should You Wear Sunscreen Every Day, All Year?
Not only is it important to protect your skin from the sun every day—regardless of what the UV index predicts—you need to make it a habit year-round. This is because UVA never lets up, even in the wintertime.
“UVA is ubiquitous and constant all year round and does not vary according to latitude or time of day,” says Dr. Laughlin. “So everyone should wear sunscreen at any time of day, in any season, in any location on the planet. The linchpin of photoprotection is to apply a sunscreen every day, first thing in the morning, regardless of your intended activity.”
But wait—there’s a catch. You also need to make sure your sunscreen gives broad-spectrum protection, and most formulas are failing when it comes to UVA.
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.
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. 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), you can estimate it yourself. According to industry sunscreen simulation tools, 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
For All Skin Tones: EleVen by Venus Williams Unrivaled Sun Serum SPF 35
If you’ve struggled with mineral sunscreens causing a white cast, EleVen by Venus Williams Unrivaled Sun Serum SPF 35 is for you. Not only is it broad-spectrum, with 25% zinc oxide, it is invisible on all skin—even the deepest tones.
For Acne-Prone Skin: Kinship Self Reflect Probiotic Moisturizing Sunscreen Zinc Oxide SPF 32
Along with its 22.4% zinc oxide, Kinship Self Reflect Probiotic Moisturizing Sunscreen SPF 32 supports acne-prone skin with probiotics and a hint of tint to blur and camouflage imperfections. It also has a light, non-greasy feel.
For Lightweight Hydration: Pipette Mineral Sunscreen SPF 50
Not only does Pipette Mineral Sunscreen SPF 50 contain 20% zinc oxide for high protection, it’s also affordably priced and hydrating enough to replace your daily moisturizer. It’s gentle enough for kids and babies, but adults of all skin types love it, too.
For Oily Skin: REN Clean Skincare Clean Screen Mineral SPF 30 Mattifying Face Sunscreen
REN Clean Screen Mineral SPF 30 Mattifying Face Sunscreen is ideal for oily skin because it has rice starch to absorb excess sebum and create a matte (but non-drying) finish. Meanwhile, it protects with 22% zinc oxide.
For All Skin: Ghost Democracy Invisible Lightweight Daily Sunscreen SPF 33
Besides 20% zinc oxide, Ghost Democracy Invisible Lightweight Daily Face Sunscreen SPF 33 contains 4% niacinamide to help with redness, dullness, large pores, excess oil and maintaining a healthy skin barrier. It’s also free of fragrance and silicones.
For Maximum Protection: CyberDerm Simply Zinc Lite Untinted Transparent Sunscreen Lotion SPF 50
CyberDerm Simply Zinc Lite Untinted Transparent Sunscreen Lotion SPF 50 is especially recommended for anyone with a history of skin cancer, hyperpigmentation or melasma. In addition to the maximum 25% concentration of zinc oxide, it is fortified with patented Bio UVA Ultra, an organic material that increases the UVA protection by up to 60%.
For Tinted Coverage: HAN Serum CC with SPF 30+
For those who prefer their sun protection with a tint, meet HAN Serum CC with SPF 30+. This CC cream comes in seven shades, is silicone-free, and gives you buildable medium-to-full coverage. Plus it’s super protective with 21% zinc oxide and 6% titanium dioxide.
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.
- 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.
- Radiation: Ultraviolet (UV) radiation. (2016, March 9). World Health Organization.
- 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.
- 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.
- Tyrrell, R. M. (1995). Ultraviolet radiation and free radical damage to skin. Biochemical Society Symposium. 1995; 61:47-53.
- Cleaver, James E. & Crowley, Eileen. (2002). UV damage, DNA repair and skin carcinogenesis. Frontiers in Bioscience. 2002 Apr 1; 7:d1024-43.
- 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.
- Health Effects of UV Radiation. (2022, January 4). United States Environmental Protection Agency.
- Lister, Roberta. (2019, June 30). This is Why You Burn so Easily – Even When Slathered in Sunscreen. Women’s Health.
- Watts, Gemma. (2020, September 23). We Asked a Dermatologist to Bust Some Sunscreen Myths. Glow Journal.
- 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.
- BASF Sunscreen Simulator.
- DSM Sunscreen Optimizer.
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