Summer and UV Exposure
It’s summer and time for outdoor fun. One of the underestimated weather risks of this time of year is UV. Solar radiation is at its most intense in July in North America and that means you need to take precautions to avoid painful sunburn and the long-term health effects of overexposure to UV.
The sun emits energy over a broad spectrum of wavelengths: visible light that you see, infrared radiation that you feel as heat, and ultraviolet (UV) radiation that you can’t see or feel. UV radiation has a shorter wavelength and higher energy than visible light. It affects human health both positively and negatively. Short exposure to UVB radiation generates vitamin D, but can also lead to sunburn depending on an individual’s skin type. Fortunately for life on Earth, our atmosphere’s stratospheric ozone layer shields us from most UV radiation. What does get through the ozone layer, however, can cause the following problems, particularly for people who spend unprotected time outdoors:
- Skin cancer
- Suppression of the immune system
- Premature aging of the skin
Types of UV Radiation
Scientists classify UV radiation into three types or bands—UVA, UVB, and UVC. The ozone layer absorbs some, but not all, of these types of UV radiation:
- UVA: Wavelength: 315-399 nm. Not absorbed by the ozone layer.
- UVB: Wavelength: 280-314 nm. Mostly absorbed by the ozone layer, but some does reach the Earth’s surface.
- UVC: Wavelength: 100-279 nm. Completely absorbed by the ozone layer and atmosphere.
UVA and UVB radiation that reaches the Earth’s surface contributes to the serious health effects listed above; it also contributes to environmental impacts. Levels of UVA radiation are more constant than UVB, reaching the Earth’s surface without variations due to the time of day or year. In addition, UVA radiation is not filtered by glass.
UV Levels Depend on a Number of Factors
The level of UV radiation reaching the Earth’s surface can vary. Each of the following factors can increase your risk of UV radiation overexposure and consequent health effects.
Stratospheric Ozone Layer
The amount of UV rays the ozone layer absorbs varies depending on the time of year and other natural events. Additionally, the ozone layer is thinner than it used to be due to ozone-depleting chemicals used in industry and consumer products. These chemicals are being phased out, but the ozone layer is not predicted to heal to pre-1980 levels until mid– to late-century.
Time of Day
The sun is highest in the sky around noon. At this time, the sun’s rays have the least distance to travel through the atmosphere and UVB levels are at their highest. In the early morning and late afternoon, the sun’s rays pass through the atmosphere at an angle and their intensity is greatly reduced.
Time of Year
The sun’s angle varies with the seasons, causing the intensity of UV rays to change. UV intensity tends to be highest in the summer.
The sun’s rays are strongest at the equator, where the sun is most directly overhead and UV rays must travel the least distance through the atmosphere. Ozone also is naturally thinner in the tropics compared to the mid- and high-latitudes, so there is less ozone to absorb the UV radiation as it passes through the atmosphere. At higher latitudes, the sun is lower in the sky, so UV rays must travel a greater distance through ozone-rich portions of the atmosphere and, in turn, expose those latitudes to less UV radiation.
UV intensity increases with altitude because there is less atmosphere to absorb the damaging rays. As a result, your chance of damaging your eyes and skin increases at higher altitudes.
Cloud cover reduces UV levels, but not completely. Depending on the thickness of the cloud cover, it is possible to burn on a cloudy day, even if it does not feel warm.
Surfaces like snow, sand, pavement, and water reflect much of the UV radiation that reaches them. Because of this reflection, UV intensity can be deceptively high even in shaded areas.
The UV Index
The UV Index provides a forecast of the expected risk of overexposure to UV radiation from the sun. The National Weather Service calculates the UV Index forecast for most ZIP codes across the U.S. The UV Index is accompanied by recommendations for sun protection and is a useful tool for planning sun-safe outdoor activities.
Ozone depletion, as well as seasonal and weather variations, cause different amounts of UV radiation to reach the Earth at any given time. Taking these factors into account, the UV Index predicts the level of solar UV radiation and indicates the risk of overexposure on a scale from 0 (low) to 11 or more (extremely high). A special UV Alert may be issued for a particular area, if the UV Index is forecasted to be higher than normal.
UV Index Forecast
The forecast map shows contour lines of predicted UV Index values during the solar noon hour. The map is created daily from National Weather Service forecast data. Click the buttons for Day 2, Day 3, or Day 4 to see the UV Index forecast for following days. You may notice a brief delay as each map loads. (To find the time of solar noon at your location, use the sunrise-sunset-solar noon calculator at the NOAA website.)
UV Protection Guidelines
Protect Your Eyes
Sunglasses are not just a fashion accessory. Sunglasses offer excellent protection for your eyes. Like your skin, your eyes are at risk of damage and trauma if exposed to too much UV radiation or “UV.”
When buying sunglasses, you can gauge their effectiveness by checking the swing tag on the sunglasses to ensure lenses block out 95% of UV. Polychromatic or colored glasses are less effective in blocking out UV. Polarizing lenses reduce glare substantially and are favored by many people for comfort, but polarization itself has little effect on the UV-absorbing properties of lenses. Similarly, mirror finishes by themselves do not significantly reduce UV absorption.
Correct use of sunglasses should begin during childhood, but no one is too old to begin wearing them. If you wear corrective lenses, you should add UV-protective coating or obtain prescription sunglasses if you spend significant periods outside. You can buy protective shades to attach to your glasses or sunglasses that you can wear over your corrective lenses.
Protect Your Skin With Suntan Lotion
Suntan lotion is used to protect your skin from the sun’s damaging ultraviolet radiation or ‘UV’. When choosing a sunscreen that will protect you, there are a few things you should know:
- No sunscreen offers 100% protection from the sun’s damaging UV. Even with sunscreen, UV will still get through to the fragile upper and lower layers of your skin.
- Sunscreen should always be used in conjunction with other forms of protection like hats, sunglasses, clothing and shade.
- Sun protection factor (SPF) 30+ sunscreen offers you maximum protection from the sun, blocking out 96% of UV. SPF 15+ will block out 93%.
- Using SPF 30+ instead of SPF 15+ does not mean you can safely double the amount of time you spend in the sun. Never use sunscreen to extend the amount of time you would normally spend in the sun.
- For sunscreen to be effective at protecting you from sunburn, slop it on 20 minutes before going outside. This gives the protective elements in sunscreen time to bond to your skin. Don’t rub it in–a light film should stay visible. Remember to reapply every two hours or more regularly if swimming or sweating a lot.
- If you experience a reaction to sunscreen, experiment with other brands first, before giving sunscreen away. It is often the fragrances or moisturizers in sunscreen that cause skin irritation. Try sensitive skin formulas or brands especially made for children.
Protect Your Skin With Clothing
Appropriately designed clothing is great for protecting you from the sun. Choose clothes that cover the arms, legs and neck to ensure you are properly protected. Go for long sleeves, collars and if possible long pants or skirts. You won’t get hot or uncomfortable if you choose lightweight fabrics like cotton, hemp or linen. The tests on clothing show that most polyester/cotton and cotton clothing items protect against 95% of ultraviolet radiation or ‘UV’. Some factors can reduce the UV protection of your clothing. If your clothing gets wet, fades or is a few years old, its ability to shade against UV will be reduced.
If you are looking for very high sun protective clothing – for outdoor work, bushwalking or for sport – choose dark colors, as they are better at absorbing UV than light colors.
Overexposure to UV radiation can impact health. Be Summer Weather-Ready. Know the impacts. For more information go to http://www2.epa.gov/sunwise/health-effects-uv-radiation.