Key Takeaways:
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UVA makes up about 95% of the UV radiation that reaches Earth's surface, and it stays constant year-round.
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UVA passes through clouds and standard window glass; UVB mostly doesn't.
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SPF number measures UVB protection only. "Broad-spectrum" is the part that confirms UVA coverage, too.
UVA and UVB are two types of ultraviolet radiation from the sun that affect the skin differently. UVB rays cause sunburn and are the primary driver of skin cancer risk, and they're more intense in summer and at high altitudes. UVA rays penetrate more deeply, causing premature aging, collagen breakdown, and discoloration, and they remain constant year-round, reaching the skin through clouds and glass. Both require broad-spectrum sunscreen for protection.
What Are UVB Rays?
UVB, or ultraviolet B , sits in the approximately 290 to 320 nanometer wavelength range: a shorter wavelength with higher energy than UVA.
UVB rays affect the skin's outer layer, the epidermis, and are the primary cause of sunburn, directly damaging DNA in skin cells. UVB is also the key driver of skin cancer risk. DNA damage in keratinocytes and melanocytes, when unrepaired, is the driving force behind most skin cancers. According to the AAD, more people are diagnosed with skin cancer each year in the United States than all other cancers combined.
UVB intensity varies quite a bit. It's strongest in summer, between 10 a.m. and 2 p.m., at high altitudes, and near reflective surfaces like water, snow, and sand, though UVB can still cause damage on overcast days.
It's worth noting that UVB triggers melanin production as a protective response. The tan that follows sun exposure is the skin's damage response mechanism.
The SPF number on a sunscreen label specifically measures UVB filtration, and that's exactly why broad-spectrum testing has to be done separately to confirm UVA coverage.
What Are the UVA Rays?
UVA, or ultraviolet A , sits in the approximately 320 to 400 nanometer wavelength range: a longer wavelength with lower energy per photon than UVB, but it makes up approximately 95% of UV radiation reaching Earth's surface.
UVA penetrates into the dermis, deeper than UVB, where it damages collagen fibers, elastin, and fibroblasts, the structural foundation of firm, smooth skin. UVA is the primary driver of photoaging: premature fine lines, loss of skin firmness, uneven pigmentation, and a leathery skin texture result from cumulative UVA exposure over years and decades.
UVA intensity is consistent year-round and throughout the day. Unlike UVB, it doesn't peak at midday or diminish significantly in winter, and it passes through clouds and through standard window glass. That means indoor, daily, and overcast-day exposure all contribute to cumulative UVA damage, which is exactly why daily SPF use matters beyond beach or outdoor situations. UVA also contributes to skin cancer risk, particularly melanoma , through oxidative damage to cellular DNA.
Why Does Broad-Spectrum Coverage Matter?
The SPF number on a sunscreen label only measures UVB filtration. It tells you nothing about UVA protection on its own.
Broad-spectrum on a sunscreen label means the formula has passed FDA testing to demonstrate protection against both UVB and UVA. It's a regulatory designation, not marketing language. A product can carry a high SPF number and still provide inadequate UVA protection if it isn't broad-spectrum. SPF 100 without broad-spectrum coverage isn't comprehensive sun protection.
The AAD recommends broad-spectrum SPF 30 or higher for daily use, and the broad-spectrum designation matters just as much as the SPF number itself.
Broad-Spectrum Protection with Marini SkinSolutions ®
At Marini SkinSolutions ® , we offer two different broad-spectrum SPF formulas, depending on your preferences.
Marini Physical Protectant SPF 45 Tinted Mineral Broad-Spectrum
Our Marini Physical Protectant SPF 45 Tinted is purely mineral, combining titanium dioxide and zinc oxide for broad-spectrum UVA and UVB protection in a photostable formula. Zinc oxide provides broad UVA1 coverage, the deeper UVA wavelengths, while titanium dioxide covers UVB and UVA2, the shorter-wave UVA. Together, they address the full UV spectrum. An oil-capture system, a universal tint in fair-to-light and light-to-medium shades, and green tea extract, alpha-bisabolol, and CoQ10 round out the formula. Purely physical protectants defend against UVA and UVB rays to help prevent UV damage and premature aging.
Antioxidant Daily Face Protectant SPF 33: Broad-Spectrum for Daily Wearability
Antioxidant Daily Face Protectant SPF 33 uses avobenzone, octinoxate, octisalate, and oxybenzone for broad-spectrum UVA and UVB protection, water-resistant up to 80 minutes, with an invisible finish. Phytomelanin, Beta-Glucan 1,3, and hyaluronic acid, paired with an oil-capture system, provide antioxidant environmental protection with daily wearability. This broad-spectrum UVA/UVB formula helps reduce the risk of premature aging from sun exposure.
Make the Most of Your Sun Protection
UVB requires protection when you're outdoors, while UVA requires protection every single day, year-round, regardless of weather or season. Broad-spectrum SPF is the answer to both, and Marini SkinSolutions ® formulates each SPF option to support daily use.
FAQs
Does UVA go through windows?
Yes. UVA rays penetrate standard window glass at near-full intensity, while UVB is largely blocked by glass. This means daily indoor exposure, like driving, sitting near windows, contributes to cumulative UVA-driven photoaging over time, which is one reason daily SPF use matters year-round.
What's the difference between UVA and UVB?
UVB rays have shorter wavelengths, higher energy, and primarily cause sunburn and direct DNA damage in skin cells. UVA rays have longer wavelengths, penetrate deeper into the skin's dermis, and are the main driver of photoaging, premature fine lines, collagen breakdown, and uneven pigmentation. Both require broad-spectrum sunscreen for protection.
Is SPF enough to protect against both UVA and UVB?
Only if the sunscreen is labeled broad-spectrum. The SPF number measures only UVB filtration. A product labeled 'broad-spectrum' has been FDA-tested to confirm UVA protection as well. The AAD recommends choosing a broad-spectrum SPF 30 or higher for daily use.
Sources:
UV-B Radiation | Colorado State University
UV Radiation & Your Skin | Skin Cancer Foundation