We all know that the sun can harm our skin—but the exact form and extent of damage depends on which UV rays we're exposed to.
There are actually two different types of UV light that reach and affect our skin. And if you want to avoid the consequences of inadequate protection (like sunburn, skin cancer and premature skin aging), you need to know the difference, and whether your sunscreen guards against both.
Spoiler: most sunscreens only do a good of defending against one of them, and in fact leave you vulnerable to 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, what they do to your skin, and which one is the most harmful
- When UV rays are the strongest and why you need to protect your skin year-round (regardless of the UV index)
- Why most sunscreens aren't actually "broad-spectrum" (despite claiming to be)
- How to choose a sunscreen that protects from both UVA and UVB, and my top product picks
What Is UV Light?
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 is measured on a scale called the electromagnetic spectrum, which also includes visible light and infrared light. Each is classified according to wavelength, which is 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 320 and 400 nanometers (nm)
- UVB is short-wave radiation between 280 and 320 nm
- UVC is intensive short-wave radiation between 100 and 280 nm
Here's how each one affects your skin.
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 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).
But 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. For that reason, 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.
What Is UVC?
Ultraviolet C (UVC) is the most intense form of UV radiation, with the shortest wavelengths of all. While this type of light is not very penetrative, it can cause severe sunburns and eye injuries.
Thankfully, we don't need to worry about UVC, since it's filtered out by the ozone layer and never reaches the Earth's surface. The only way you'd be exposed to UVC is through man-made sources such as specialized lasers or lamps (typically used for disinfection).
Which Type of UV is the Most Harmful?
So, which type of UV should you be the most worried about: UVA or UVB?
"The most damaging rays from the sun are in fact in the UVA spectrum," says Dr. Howard Murad, dermatologist and founder of Murad, in an interview with Women's Health. "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."
UVA is also far more prevalent than UVB. Surprisingly, it accounts for 95% of the UV light that reaches the Earth, whereas UVB is only 5%.
According to the World Health Organization, "up to 90% of the visible changes commonly attributed to aging may be caused by sun exposure," and we know that UVA is the main culprit.
When Are UV Rays the Strongest?
The strength of UV radiation reaching the Earth (and your skin) depends on several factors:
- 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.
What Is the UV Index?
The UV index is an international measurement system that predicts the level of UV radiation on any given day. It takes the above factors into account—the time of day, the season, your specific location and the local weather conditions—to come up with a UV reading on a scale of 0 to 11+.
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.
"It's really a vehicle for public awareness," says Dr. Cara McDonald, dermatologist and director of Complete Skin Specialists Dermatology, in an interview with Glow Journal. "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."
So if you're hoping to avoid future wrinkles and sun spots, relying on the UV index may still put you at risk. "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," adds Dr. McDonald. "So, personally, I would just suggest that we wear [sunscreen] all the time, particularly in those areas that are frequently exposed, like the face."
Do You Really Need UV Protection Year-Round?
Not only is it important to protect your skin 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."
Does Sunscreen Block UVA and UVB?
These days, sunscreens are almost always labelled "broad-spectrum," which means they promise to protect your skin from both UVA and UVB.
Unfortunately, most of them are failing when it comes to 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 (UVA-PF).
According to Dr. Laughlin, a truly broad-spectrum sunscreen needs to be SPF 30 or higher, with a UVA-PF of at least 10-20.
The problem is, the FDA and Health Canada don't require UVA-PF testing—even though it's 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.
As a result, 90% of sunscreens on the market only achieve a UVA-PF of 5-8, which is way too low. And without high UVA protection, they have little if any chance of preventing skin cancer or premature skin aging.
"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 UVA-PF 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 UVA-PF values."
How to Make Sure Your Sunscreen Is Actually “Broad-Spectrum”
How do you find a sunscreen that protects from both UVA and UVB, when so many of them aren't doing their jobs properly?
Since brands aren't required to perform the UVA-PF 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 UVA and UVB. (It also happens to be the safest filter, since it remains on the skin surface instead of absorbing into your body.) Your sunscreen should have a minimum 15% concentration up to a maximum of 25%.
- SPF 30 or higher: SPF is a measure of how well a sunscreen guards against UVB rays. Since many companies fail to meet the SPF claims on their labels, you can estimate this number yourself. 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, which primarily guards against UVB. 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.
The Best Broad-Spectrum Sunscreens to Protect From UVA and UVB
For All Skin Tones: EleVen by Venus Unrivaled Sun Serum SPF 35
If you've struggled with mineral sunscreens causing a white cast, EleVen by Venus 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 SPF 32
Besides its light and non-greasy feel, Kinship Self Reflect Probiotic Moisturizing Sunscreen SPF 32 supports acne-prone skin with probiotics and a hint of tint (which helps blur and camouflage imperfections). It also protects with a high 22.4% zinc oxide.
For Oily Skin: REN 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 Sensitive Skin: NUORI Mineral Defence Sunscreen SPF 30
NUORI Mineral Defence Sunscreen SPF 30 is free of fragrance and preservatives, and (like all products from this brand) is made in small batches every 10-12 weeks for maximum freshness. It has 23% zinc oxide sunscreen, and also doubles as a makeup primer.
For Dry Skin: Pipette Mineral Sunscreen SPF 50
If you're looking for a hydrating sunscreen that could replace your daily moisturizer, Pipette Mineral Sunscreen SPF 50 should fit the bill. It's packed with humectants and fatty acids, plus 20% zinc oxide, and leaves your skin with a subtly dewy finish.
For All Skin Types: Ghost Democracy Invisible Lightweight Daily Face Sunscreen SPF 33
Niacinamide is the one ingredient I recommend for everyone, and there's 4% of it in Ghost Democracy Invisible Lightweight Daily Face Sunscreen SPF 33 to help with redness, dullness, large pores, excess oil and maintaining a healthy skin barrier. It also has 20% zinc oxide and is free of fragrance and silicones.
For Tinted Coverage: HAN Serum CC SPF 30+
For those who prefer their sun protection with a tint, meet HAN Serum CC 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.
For the Highest 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%.
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."
I don't know about you, but hearing that statistic makes me extra-motivated to be diligent about UV protection, no matter what!
If you buy something through our links, we may earn a commission. See our Disclosure for more information.