Ultraviolet Radiation and the UV Index
About Ultraviolet Radiation
- Is an invisible form of light and energy given off primarily by the sun
- Can penetrate the upper layers of our skin
- Is absorbed by DNA and can change its structure (causing mutations)
- Some DNA changes can be corrected–if not, changes can lead to unchecked cell growth (ie, cancer)
- If you are exposed to frequent and intense UV radiation, you are exposed to one of the major risk factors for melanoma.
There are 3 types of UV rays:
- UVA (Long wavelength)
- Penetrate deeply
- Associated with wrinkling / leathering of skin
- Makes UVB-induced damage worse
- Directly stimulates skin cancers
- UVB (Medium wavelength)
- Burning waves
- Primary cause of sunburn
- Main cause of basal cell and squamous cell carcinoma as well as cause of melanoma
- UVC (Short wavelength)
- Absorbed by ozone layer
- Not thought to induce skin cancer
Although both UVA and UVB can cause damage, the skin reacts differently to each one.
Comparison of UVA and UVB
Less potent, but constitutes the bulk of UV radiation reaching the earth
More potent, leading to more DNA damage and cancer risk
Long-term: damage to dermis leads to thinning and aging of the skin
Short-term; epidermis releases chemicals leading to reddening / swelling (early signs of sunburn)
Long-term: repeated exposure leads to injury and aging skin
Can penetrate glass
Cannot penetrate glass
The UV Index
The UV Index was designed to help you make informed decisions about how much time you should spend in the sun and what protection you should use. It was created by the Environmental Protection Agency, the National Weather Service, and the Centers for Disease Control and Prevention. The UV Index is issued daily, and tells you how strong the sun’s UV rays will be. The higher the UV Index, the greater the strength of the sun’s UV rays and the faster you may burn.
The index predicts the risk of UV overexposure on a scale of 0 (minimal risk) to 11+ (very high risk). The forecast considers latitude, elevation, weather conditions, time of year and the ozone levels in your region. The index is based on a type 2 skin type (fair skin, burns easily, tans minimally)
The chart below shows the levels of the UV Index and what you should do to protect yourself.
UV Index 0-2 means minimal danger from the sun’s UV rays for the average person. Most people can stay in the sun for up to 1 hour during peak sun (10am to 4pm) without burning. However, people with very sensitive skin and infants should always be protected from prolonged sun exposure.
UV Index 3-5 means low risk of harm from unprotected sun exposure. Fair skinned people however, may burn in less than 20 minutes. Wearing a hat with a wide brim and sunglasses will protect your eyes. Always use a sunscreen with an SPF of at least 30, and wear long-sleeved shirts when outdoors.
UV Index 6-7 means moderate risk of harm from unprotected sun exposure. Fair skinned people however, may burn in less than 20 minutes. Wearing a hat with a wide brim and sunglasses will protect your eyes. Always use a sunscreen with an SPF of at least 30, and wear long-sleeved shirts when outdoors. Remember to protect sensitive areas like the nose and the rims of the ears. Sunscreen prevents sunburn and some of the sun’s damaging effects on the immune system. Use a lip balm or lip cream containing a sunscreen. Lip balms can help protect some people from getting cold sores.
UV Index 8-10 means high risk of harm from unprotected sun exposure. Fair skinned people however, may burn in less than 10 minutes. Minimize sun exposure during midday hours of 10am to 4pm. Protect yourself by liberally applying a sunscreen of at least 30. Wear protective clothing and sunglasses to protect the eyes. When outside, seek shade. Don’t forget that water, sand, pavement and glass reflect UV rays even under a tree, near a building or beneath a shady umbrella. Wear long sleeved shirts and trousers made from tightly-woven fabrics. UV rays can pass through the holes and spaces of loosely knit fabrics.
UV Index of 11+ means very high risk of harm from unprotected sun exposure. Fair skin people however, may burn in less than 5 minutes. Outdoor workers and vacationers who can receive very intense sun exposure are especially at risk. Minimize sun exposure during midday hours of 10am to 4pm. Apply SPF 30+ sunscreen every 2 hours. Avoid being in the sun as much as possible and wear sunglasses that block out 99-100% of all UV rays (UVA and UVB). Wear a cap or a hat with a wide brim which will block roughly 50% of UV radiation from reaching the eyes.
Remember to check the UV Index each day.