About UV Rays
Overview
Skin reacts to UV radiation by a change in the melanin content. Under strong radiation or conditions of slow change, the familiar reddening (“erythema”) occurs, followed by sunburn and soreness. Human racial groups vary by hair color, skin color, eye type and reaction to exposure to UV radiation. There are six recognized skin types as regards the effects of UV.
Skin type, definition & reaction
- Red or blond hair, blue-green eyes very light shin –> Mostly burns, does not tan
- Light-medium hair, eyes and skin –> Usually burns, seldom tans
- Medium hair, medium to dark eyes, medium to olive skin –> Moderately burns, lightly tans
- Dark hair, eyes dark, olive to light brown skin –> Burns mildly, tans to moderate brown
- Dark hair, eyes and skin –> Seldom burns, tans to dark brown
- Dark hair, eyes and very dark skin –> Insensitive, does not burn
How does this range affect you? The permissible time for exposure to UV radiation on a midsummer day at sea level at or near the equator without using sunscreen ranges from 20 minutes for individuals with Skin Type 2, to 100 minutes for those with Skin Type 4.
The erythemal potential due to exposure to UV radiation is usually referred to in units of Minimum Erythemal Doses (“MED”) caused by the exposure. One MED is defined as the amount of UV radiation that produces a just noticeable erythema on previously unexposed skin, and is different for the different skin types.
Most people are unaware of the damage that can be caused even after exposure to low intensity UV radiation, because the dose is accumulated during exposure of varying duration at different times in a daily routine. Usually the first visible sign is the sunburn, which might appear a few hours after the exposure, while skin cancer may appear years later. This means that the individual becomes aware of the danger after the damage has been done.
Most people do not routinely use sunscreens unless they are on the beach or a trip. Even then, they usually do not apply the sunscreens periodically, as they should because it gradually dissipates through perspiration and absorption in the skin.
Altitude, latitude, season, air pollution, clouds, and other factors influence the effective UV radiation level. Therefore it is very difficult to give accurate, reliable and timely warnings to the public about the UV radiation levels for specific location and day time.
The only practical means of protection is a personal dosimeter, a device that measures and indicates the amount of radiation absorbed in a given period.
Currently UVSunSense manufactures and sells a personal dosimeter in the form of a wristband for people with skin type 1 and all children regardless of their skin type. Coming soon will be two additional bands; Bands, one made for skin types 2 & 3 and another for skin types 4 & 5.
As a safety precaution, each band type is calibrated to finish when it has absorbed 1/2 of the Minimum Erythemal Dose (“MED”) of radiation for the particular skin type it was designed for.
UV Measurement:
| milliWatts per
square meter | Index Value | Exposure Category |
| <60 | Less than 3 | Moderate |
| 60 – 150 | 3 – 6 | High |
| 151 – 580 | 6 – 10 | Very High |
| > 580 | Greather than 10 | Extreme |
When the UV-Index is 3 (“60 milliWatts or less”), a fair skinned person will experience minimal skin redness after one hour in the sun. When the UV-Index is 6 (“150 milliWatts or less”) , a fair skinned person will experience minimal skin redness after 24 minutes in the sun and when the UV-Index is 10, a fair skinned person will experience minimal skin redness after 6 minutes in the sun. UV-Index levels over 7, around 250 milliWatts per square meter are common and will result in a fair skinned person burning after 15 minutes in the sun.
Remember, potential long term health effects from UV radiation do not depend on skin type.
UV Radiation
The sun radiates energy over a broad spectrum of wavelengths. Ultraviolet (“UV”) radiation, which has a shorter wavelength than either visible blue or violet light, is responsible for sunburn and other adverse health effects. Fortunately for life on Earth, our atmosphere’s stratospheric ozone layer shields us from most UV radiation. What gets through the ozone layer, however, can cause the following problems, particularly for people who spend substantial time outdoors:
- Skin cancer
- Cataracts
- Suppression of the immune system
- Premature aging of the skin
Because of these serious health effects, you should limit your exposure to UV radiation and protect yourself when outdoors.
Types of UV Radiation
Scientists classify UV radiation into three types or bands—UVA, UVB, and UVC. The stratospheric ozone layer absorbs some, but not all, of these types of UV radiation:
UVA: Not absorbed by the ozone layer.
UVB: Mostly absorbed by the ozone layer, but some does reach the Earth’s surface.
UVC: Completely absorbed by the ozone layer and oxygen. UVA and UVB that reach the Earth’s surface contribute to the serious health effects listed above.
UV Levels Depend on a Number of Factors:
The level of UV radiation that reaches the Earth’s surface can vary, depending on a variety of factors. Each of the following factors can increase your risk of UV radiation overexposure and its consequent health effects.
Stratospheric Ozone: The ozone layer absorbs most of the sun’s UV rays, but the amount of absorption varies depending on the time of year and other natural phenomena. That absorption also has decreased, as the ozone layer has thinned due to the release of ozone-depleting substances that have been widely used in industry.
Time of Day: The sun is at its 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 during the summer months.
Latitude: 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.
Altitude: UV intensity increases with altitude because there is less atmosphere to absorb the damaging rays. Your risk of overexposure increases as you go to higher altitudes.
Weather Conditions: Cloud cover reduces UV levels, but not completely. Depending on the thickness of the cloud cover, it is possible to burn and increase your risk of long-term skin and eye damage. You can burn on a cloudy summer day, even if it does not feel very warm.
Reflection: Some surfaces, such as snow, sand, grass, or water can reflect much of the UV radiation that reaches them. Because of this reflection, UV intensity can be deceptively high even in shaded areas.
Credits
National Association of Physicians for the Environment
American Medical Association
Wilderness Medical Society
American Skin Association
American Academy of Dermatology
American Academy of Otolaryngology
American Academy of Ophthalmology
American Academy of Optometry
American Society for Head and Neck Surgery
American Optometric Association
American Society of Plastic and Reconstructive Surgeons
Coalition of Patient Advocates for Skin Disease Research
Society for Investigative Dermatology
Skin Cancer Foundation | Friends of the Earth
National Medical Association
Lupus Foundation of America, Inc.
Ozone Action, Inc.
Alliance for Environmental Education
Association of University Environmental Health Sciences Centers
Prevent Blindness America
Save Our Sky
North American Association for Environmental Education
NAPE National Office for the Protection of Biodiversity (Galveston, TX)
National Association 0f County & City Health Officials (NACCHO)
Environmental Alliance for Senior Involvement (EASI)
Association of State & Territorial Health Organizations (ASTHO) |
