difference between uva and uvb

Warm summer days offer plenty of ways to have fun in the sun, but you could damage unprotected skin in as little as 15 minutes.

Shielding your skin from the sun’s ultraviolet (UV) rays is one of the most important things you can do to prevent skin cancer, premature aging, and other types of sun damage.

Broad-spectrum sunscreen of at least SPF 30 blocks up to 97% of the sun’s rays. You’ll need about one ounce — or a shot glass full — of sunscreen to cover your whole body and face. Reapply every two hours, or more often if you’ll be in the water or sweating heavily. The sun’s rays shine strongest between the hours of 10 a.m. and 4 p.m., so use extra caution during that time period.

What is UV Light?

Ultraviolet or UV light is radiation energy from the sun, which comes in two forms: UVA and UVB. UVC radiation, while not originating from the sun, is also dangerous and harmful to the skin. UV radiation is a wavelength too short for the human eye to see.

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Types of UV Rays

  • UVA – The most common UV ray from the sun and most dangerous, UVA can penetrate the skin down to the middle layer.
  • UVB – A shorter wavelength than UVA that can only penetrate the skin to the top layer. Some UVB rays are stopped by the earth’s ozone layer; it can also be stopped by treated glass.
  • UVC – All UVC rays from the sun are stopped by the ozone layer; therefore, the only exposure humans get to UVC is from artificial sources such as lasers or welding torches.

Learn Your ABCs: UVA, UVB, and UVC Rays

The sun emits three different types of UV radiation: UVA, UVB, and UVC.

All types of UV radiation have the potential to damage your skin, but each type affects your skin differently. UVA rays, which account for 95% of radiation that reaches the earth’s surface, cause wrinkles, sun spots, and other types of premature aging. They are also strongly linked to skin cancer. UVB rays, which affect skin’s top layer, cause skin cancer and most sunburns.

Although UVA and UVB rays pose the greatest risk for sun damage, people who work with welding torches or mercury lamps may be exposed to UVC rays — the most dangerous type of UV radiation.

How do you tell the different UV rays apart and how do they affect your skin?

Check out the infographic below to learn your ABCs!ABCsofUV.png

UVA rays

The sun is the main source of all UV rays on earth. However, man-made sources of UVA rays can include lights made to mimic sunlight for therapy or tanning purposes. UVA rays can be deflected off the skin by using sunscreen with an SPF of 30 or greater.

UVB rays

The earth’s ozone layer prevents some UVB rays from reaching the earth’s surface. However, it does not stop all UVB rays, which can penetrate the skin deeper than UVA rays. Luckily UVB rays cannot pass through glass, so you are protected from UVB rays when in the car or at home. Sunscreen of SPF 30 or greater also will deflect UVB rays.

UVC rays

UVC rays come from the sun, but the earth’s ozone layer prevents all UVC rays from reaching the earth’s surface. Man-made sources of radiation, however, such as lights, welding torches, or lasers also can emit UVC rays. UVC rays cannot penetrate the skin as deeply as UVA or UVB, but UVC rays can be particularly harmful to the eyes. Never look directly at a UVC light source.

Which Type of UV Ray is the Most Harmful?

Consistent, unprotected exposure to any source of UV radiation can be harmful. UVC rays penetrate the body the least, mostly effecting weak points such as the eyes. UVA rays can only penetrate the first layer of skin, while UVB rays can penetrate to the middle layer of skin and cause deep cancerous spots known as melanoma.

Which UV Ray Causes Sunburn?

UVA rays are most likely to cause sunburns as they are the most prominent type of UV ray on earth. UVA rays will also penetrate the skin down to the middle layer (dermis). UVB rays can penetrate the top layer of skin, meaning they can also cause sunburn. There is very little difference in the type of burn and no clear way to tell what type of UV ray caused your sunburn.

What Type of UV Ray Causes Melanoma?

Consistent, unprotected exposure to UVA or UVB rays can cause melanoma, however UVB rays will penetrate the skin the deepest where melanoma originates. While it is difficult to eliminate UV exposure, it can be reduced by covering exposed portions of the body, wearing sunscreen, or wearing sunglasses. However, reducing exposure to UV rays may not prevent melanoma. Keep an eye on any changes in existing moles — or a new mole with an irregular shape or color — as it may be a sign of melanoma.

Protecting Yourself

Summer days should be spent enjoying a little bit of sunshine — not worrying about the harmful effects of the sun and UV rays. By arming yourself with sunscreen, protective clothing, and the right sunglasses, you can safely enjoy outdoor activities today without fear of damage to your skin tomorrow.

If you are concerned about any abnormal moles or skin discolorations as a result of years of unprotected sunbathing, please visit the UPMC Hillman Cancer Center website or call 412-647-2811 to schedule an appointment.



Editor's Note: This article was originally published on , and was last reviewed on .

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