What’s the difference between UVA and UVB rays?
November 25, 2025
Medically Reviewed | Last reviewed by Saira George, M.D., on November 25, 2025
If you’re interested in staying safe in the sun, you’ll hear a lot about ultraviolet radiation. That’s because UV rays are the part of sunlight that causes skin cancer and skin aging.
Tanning beds also emit UV radiation. Tanning beds cause the same skin damage as the sun.
It’s helpful to know how these rays work, so you know how to protect yourself. Know your enemy, right?
To learn more, we spoke to Saira George, M.D., a dermatologist at MD Anderson in Sugar Land.
Key takeaways:
- The two types of ultraviolet radiation that reach Earth are UVA and UVB rays.
- Most of our UV exposure comes from UVA rays, which can penetrate deeply into the skin. UVA contributes to skin cancer and causes tans, skin aging and wrinkles.
- UVB rays don’t penetrate the skin as deeply as UVA rays, but they can damage skin cells and cause DNA mutations that lead to skin cancer.
- Protect yourself from UVA and UVB rays by staying out of the sun when UV intensity is highest and choosing a broad-spectrum sunscreen that is at least 30 SPF and water resistant.
What is UV radiation?
It may seem odd, but the sun does not emit only one kind of light. Sunlight sends a whole spectrum of light down to us here on Earth.
Some parts of that spectrum of light are obvious to us. For example, infrared radiation is what heats us up. We may not see it, but we can feel it.
Ultraviolet radiation is at the other end of the light spectrum. Some kinds of insects can see UV, but humans can’t. And we don’t feel it until it’s too late.
UV radiation can burn and damage our skin without causing us to feel warm. That’s why it is dangerous even on cloudy days.
Not all UV radiation from sunlight makes it to Earth. Most of it gets absorbed by our atmosphere. But two kinds of UV rays do break through. They are called UVA and UVB radiation.
What is UVA radiation?
UVA radiation makes up 95% of the UV rays that make it to the Earth’s surface. UVA rays have a longer wavelength than UVB rays, which allows them to penetrate deeper into our skin. They can even pass through glass.
UVA damages your skin, resulting in a tan. It is the primary radiation used in tanning beds. It causes almost all forms of skin aging, including wrinkles. UVA damages the collagen and elastin in the skin and also generates free radicals.
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And recent research shows it doesn’t end there.
“UVA partners up with UVB to cause more serious problems, like skin cancer,” George says.
What is UVB radiation?
UVB radiation makes up only 5% of the UV rays from the sun, but it is very high-energy.
“UVB does not penetrate as deeply as UVA, but it can wreak havoc on the top layers of your skin,” George says.
UVB damages skin cells and causes DNA mutations that can eventually lead to melanoma and other types of skin cancer.
How to protect yourself
The best way to protect yourself from UV radiation is to stay out of the sun between 10 a.m. and 4 p.m., when UVB rays are at their highest intensity.
It’s important to take care of yourself, even if you are in the shade. UV rays can reflect off surfaces like concrete, water, sand and snow, and still cause significant damage to your skin.
If you go out in the sun, use a sunscreen with SPF 30 or higher. Make sure you choose one that is water-resistant and offers broad-spectrum protection.
Broad-spectrum sunscreens reflect and absorb UV radiation. They ensure you are protected from both UVA and UVB radiation. Apply sunscreen at least 30 minutes before going out in the sun and reapply after swimming or sweating.
And don’t underestimate the amount of protection you can get by covering up.
“Clothing can be more reliable,” George says. “A sun-protective shirt can really help you fill in the gaps that sunscreen leaves.”
Shop for MD Anderson-branded UPF gear.
Finally, wear a wide-brimmed hat to shade your head and face, and use UV-protective sunglasses.
Request an appointment at MD Anderson online or call 1-877-632-6789.
UVA partners up with UVB to cause more serious problems, like skin cancer.
Saira George, M.D.
Physician