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UV Radiation


Updated May 15, 2014

Sunlight has a profound effect on the skin causing premature skin aging, skin cancer, and a host of skin changes. Exposure to ultraviolet light, UVA or UVB, from sunlight accounts for 90% of the symptoms of premature skin aging. Many skin changes that were commonly believed to be due to aging, such as easy bruising, are actually a result of prolonged exposure to UV radiation.

What Is UV?

The sun gives off ultraviolet radiation that we divide into categories based on the wavelength.
  • UVC - 100 to 290 nm
  • UVB - 290 to 320 nm
  • UVA - 320 to 400 nm


UVC radiation is almost completely absorbed by the ozone layer and does not affect the skin. UVC radiation can be found in artificial sources such as mercury arc lamps and germicidal lamps.


In a nutshell, UVB affects the top layer of skin, the epidermis, causing sunburns. Specifically:
  • About 90% of UVB radiation is absorbed by the ozone layer.
  • As the ozone layer gets depleted, we are exposed to more UVB radiation.
  • UVB is the most intense between the hours of 10:00 am and 2:00 pm when the sunlight is brightest.
  • UVB is also more intense in the summer months.
  • 70% of a person's yearly UVB dose occurs in the summer.
  • UVB does not penetrate glass.


In general UVA affects the deeper layer of the skin, the dermis, and causes changes that lead to photoaging and skin cancer. Specifically:
  • The ozone layer has no effect on UVA rays.
  • UVA penetrates deeper into the skin and works more efficiently.
  • The intensity of UVA radiation is more constant than UVB without the variations during the day and throughout the year.
  • UVA does go through glass.

UVA and UVB Work Together

Because of other atmospheric filters besides ozone, most of the UV radiation that reaches us is UVB, about 20 times more than UVA. Even though we think of UVB as the sunburn producer and UVA the wrinkle and skin cancer producer, they both work together to cause skin damage including:
  • Wrinkles
  • Lowered immunity against infection
  • Aging skin disorders
  • Cancer

Damaging Effects of UVA and UVB

Some of the ways these UV rays cause skin damage include:
  • They both cause damage to DNA, UVB in the epidermis and UVA deeper in the dermis.
  • This damage causes mutations in the p53 tumor suppressor gene, a gene responsible for either repairing damaged DNA if possible or discarding cells that are damaged beyond repair.
  • If p53 doesn't function properly these highly damaged cells are allowed to continue dividing, creating even more highly damaged cells.
  • Around 50% of skin tumors have this mutated p53 gene in them.
  • UVA penetrates deeper into the skin reaching the dermis where collagen, the structural scaffolding of the skin, is located. This causes the skin to sag in places leading to wrinkles.
  • Both UVA and UVB cause the number of Langerhans cells, an important part of the immune system, to decrease, lowering immunity.
  • UVA increases the number of inflammatory cells in the dermis.

What Does This Mean for Me?

The scary part of all of this: You can't feel or see any of these mutations happening until the damage has already been done. Most of this damage occurs in childhood. This means it's extremely important to use sunscreen and sun-protective clothing at all times. Even young children need to be protected any time they go outside, not just when they're swimming.


Marrot, L, and JR Meunier. “Skin DNA Photodamage and Its Biological Consequences.” Journal of the American Academy of Dermatology 58.5 Suppl 2 (2008): S139-48.

Palm, Melanie, and Marianne O'Donoghue. “Update on Photoprotection.” Dermatologic Therapy 20(2007): 360-76.

Rigel, DS. “Cutaneous Ultraviolet Exposure and Its Relationship to the Development of Skin Cancer.” Journal of the American Academy of Dermatoly 58.5 Suppl 2 (2008): S129-32.

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