Ultraviolet Light and Your Skin

Cancer Information Service
Holden Comprehensive Cancer Center
University of Iowa Hospitals and Clinics

Creation Date: May 2004
Last Revision Date: June 2006
Peer Review Status: Internally Peer Reviewed

Although you may enjoy having a "golden glow," any tan is a sign of skin damage that can result in skin cancer. Tanning occurs when the skin produces additional pigment or coloring to protect itself from ultraviolet rays.

Ultraviolet B rays are burning rays (blocked by window glass) that are the primary cause of sunburns and skin cancer. Ultraviolet A rays (penetrate through window glass) are able to penetrate deeper into the dermis or the base layer of the skin. UV A rays also contribute to skin burning and cancer. Both UV A and B rays can suppress the immune system, which helps protect against the development and spread of skin cancer.

The National Weather Service and the U.S. Environmental Protection Agency developed the ultraviolet index. The index provides important information so that you can plan your outdoor activities to prevent overexposure to the ultraviolet rays of the sun.

The Index predicts the risk of overexposure to the sun by measuring the ultraviolet light intensity levels on a scale of 0 to 11+.

Precautions against overexposure should always be taken. To check the daily UV index for your area, visit the U.S. Environmental Protection Agency website. You can also sign up for a daily e-mail of the UV rating in your area. When the UV Index levels are moderate or above 5+ special measures should be taken to protect against overexposure, including,

• Avoid exposure during peak sunlight hours, 10:00 a.m. to 4:00 p.m.
• Children younger than 6 months should be kept out of direct sunlight.
• Wear protective, tightly woven clothing, such as a broad-brimmed hat, shirt, and pants. (A hat brim of 4 inches or greater is recommended.) Dark colors give more protection.
• Apply a broad-spectrum sunscreen 30 minutes before going outdoors. It should have a SPF of at least 15 or higher, and protect against both ultraviolet A and B rays. One ounce is considered the amount needed to cover the exposed areas of the body properly.
• Reapply sunscreen every two hours (sunscreens used on a regular basis actually allow some repair of damaged skin).
• Protect yourself even on a cloudy day: 80% of the sun's ultraviolet rays will pass through the clouds.
• Wear sunglasses with ultraviolet protective lenses.
• Seek shade whenever possible.
• Avoid reflective surfaces.
• Avoid artificial sources of UV light such as sun lamps and tanning beds.
• Use sun protection measures when traveling by motor vehicle to block out harmful UVA rays that can penetrate through window glass.

Sunscreens

Most people benefit from sunscreens with a sun protection factor (SPF) number of 15 or more. The SPF number tells you about how long you can stay in the sun without burning. For example, if you normally burn in 10 minutes without sunscreen and you've applied a liberal dose of sunscreen with an SPF of 15, you should be protected from sunburn for 150 minutes.

Sunscreens should always be used if you plan to spend more than 20 minutes in the sun. To get the maximum protection from your sunscreen, apply at least one large handful (about 1 ounce) 30 minutes before you go outside. The sunscreen should be reapplied throughout the day and after swimming, toweling dry, or participating in any activity that causes heavy perspiration.