UVA is the type of ultraviolet radiation most responsible for skin aging, and it makes up roughly 95% of the UV light that reaches you from the sun. Unlike UVB, which burns the outer layer of skin, UVA penetrates deeper into the tissue beneath, where it damages the structural proteins that keep skin firm and smooth. Its effects go beyond cosmetics: UVA also contributes to DNA damage, eye disease, and skin cancer risk through mechanisms that are subtle, cumulative, and easy to underestimate.
How UVA Differs From Other UV Rays
Ultraviolet radiation spans wavelengths from 100 to 400 nanometers and is split into three bands. UVC (100 to 280 nm) is the most energetic but gets absorbed entirely by the atmosphere. UVB (280 to 315 nm) reaches the surface in small amounts and is the main cause of sunburn. UVA (315 to 400 nm) has the longest wavelength, the lowest energy per photon, and by far the greatest presence in sunlight.
That lower energy is deceptive. Because UVA wavelengths are longer, they pass through the outer skin layer (the epidermis) and reach the deeper layer underneath (the dermis), where collagen and elastin fibers live. UVB mostly affects the surface. This deeper penetration is why UVA causes a different kind of damage: less visible in the short term, more consequential over years.
Skin Aging and Wrinkle Formation
The most well-documented effect of UVA is photoaging, the premature aging of skin driven by sun exposure rather than time. When UVA reaches the dermis, it generates unstable molecules called reactive oxygen species. At high enough concentrations, these molecules trigger a chain reaction: they activate enzymes that break down collagen, elastin, and other structural proteins holding your skin together. The result, over months and years, is thicker wrinkles, sagging, and a leathery texture that wouldn’t develop from aging alone.
The breakdown is surprisingly specific. UVA-triggered signaling ramps up the production of at least three key enzymes that digest collagen fibers. Separately, another enzyme with strong elastin-degrading activity contributes to a condition called solar elastosis, where damaged elastic tissue clumps together under the skin surface. This is why chronically sun-exposed skin on the face, neck, and hands looks so different from skin that’s usually covered.
UVA also kills fibroblasts, the cells in the dermis responsible for producing new collagen. So it’s a double hit: existing collagen gets broken down faster while the cells that would replace it are lost.
DNA Damage and Cancer Risk
UVB has long been considered the primary cancer-causing UV wavelength because it directly damages DNA. UVA works differently, but that doesn’t make it harmless. Instead of striking DNA directly, UVA activates light-sensitive molecules already inside your cells. These molecules generate reactive oxygen species that damage DNA indirectly, causing oxidized bases, breaks in the DNA strand, and abnormal crosslinks between DNA and nearby proteins.
Perhaps more importantly, UVA appears to sabotage your body’s ability to repair the DNA damage that UVB causes. Research has shown that UVA-generated reactive oxygen species can oxidize and disable repair proteins in human cells, making it harder for your normal repair machinery to fix UVB-induced mutations. The effect is subtle and cumulative: each exposure slightly reduces repair efficiency, and unrepaired mutations accumulate over a lifetime. This is one reason researchers believe UVA and UVB together are more dangerous than either would be alone, and why total UV protection matters more than just preventing sunburn.
Effects on the Eyes
UVA contributes to cataract formation, a clouding of the eye’s lens that is one of the leading causes of vision loss worldwide. Both UVA and UVB are risk factors for cataracts, and neither wavelength is needed for sight. UV exposure is also a risk factor for retinal damage, particularly in children, whose lenses transmit more UV light than adult lenses do. Wearing sunglasses that block both UVA and UVB substantially reduces these risks over time.
UVA Does Not Produce Vitamin D
One common misconception is that any sun exposure helps your body make vitamin D. In reality, vitamin D synthesis in the skin is driven almost entirely by UVB. In controlled trials, UVB exposure significantly raised blood levels of vitamin D, while UVA exposure at the same dose did not produce a meaningful increase. Longer UVA sessions actually showed a lower rise in vitamin D levels compared to equivalent UVB exposure. This matters because tanning beds, which emit up to 98% UVA radiation, are sometimes marketed as a source of vitamin D. They are not an effective one.
UVA Passes Through Glass and Clouds
UVA behaves differently from UVB in the environment in ways that catch people off guard. Standard window glass blocks virtually all UVB but lets a significant portion of UVA through. In cars, front windshields (which are laminated) block about 99% of UVA. Side windows, however, average only about 89% UVA attenuation, meaning roughly 11% still reaches the driver. This is part of why studies consistently find more sun damage on the left side of the face and left arm in countries where people drive on the right.
Cloud cover also reduces UVA far less than most people assume. On an overcast day, you can still receive substantial UVA exposure without feeling warmth or noticing any reddening, since UVA doesn’t cause sunburn the way UVB does.
Tanning Beds and Concentrated UVA
Commercial tanning beds emit roughly 12 times more UVA radiation than midday sun. Because UVA stimulates melanin production (tanning) without the immediate feedback of a burn, tanning beds were long marketed as a “safer” alternative to outdoor sun. The biology tells a different story. That concentrated UVA dose accelerates every mechanism described above: collagen destruction, fibroblast death, oxidative DNA damage, and impaired DNA repair. The World Health Organization classifies tanning beds as a Group 1 carcinogen, the same category as tobacco.
How UVA Protection Works in Sunscreen
SPF, the number on every sunscreen bottle, measures protection against UVB. UVA protection uses a separate system. In many Asian and European markets, the PA rating (Protection Grade of UVA) tells you how much UVA a sunscreen blocks:
- PA+: some UVA protection
- PA++: moderate UVA protection
- PA+++: high UVA protection
- PA++++: extremely high UVA protection
In the United States, look for “broad spectrum” on the label, which means the product has been tested for UVA coverage. Ingredients like zinc oxide and avobenzone are among the most effective UVA filters. Since UVA penetrates glass and is present even on cloudy days, daily broad-spectrum protection matters more than most people realize, not just on beach days but during commutes, desk work near windows, and any extended time outdoors.