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. UV radiation is classified as a human carcinogen, according to the U.S. Department of Health and Human Services and the World Health Organization.
While some exposure to sunlight can be enjoyable, too much can be dangerous. Overexposure to UV radiation from the sun can result in painful sunburn. It can also lead to more serious health problems. Most people are not aware that skin cancer, while largely preventable, is the most common form of cancer in the United States.
More than one million cases of skin cancer are reported annually. One in five Americans will develop skin cancer in their lifetime. One American dies from skin cancer every hour. Unprotected exposure to UV radiation is the most preventable risk factor for skin cancer.
Melanoma, the most serious form of skin cancer, is now one of the most common cancers among adolescents and young adults ages 15-29. While melanoma accounts for about three percent of skin cancer cases, it causes more than 75 percent of skin cancer deaths. UV exposure and sunburns, particularly during childhood, are risk factors for the disease. Not all melanomas are exclusively sun-related—other possible influences include genetic factors and immune system deficiencies.
Non-melanoma skin cancers are less deadly than melanomas. Nevertheless, they can spread if left untreated, causing disfigurement and more serious health problems. There are two primary types of non-melanoma skin cancers: basal cell and squamous cell carcinomas. If caught and treated early, these two cancers are rarely fatal. Between 40 and 50 percent of Americans who live to age 65 will have one of these types of skin cancer at least once.
Basal cell carcinomas are the most common type of skin cancer tumors. They usually appear as small, fleshy bumps or nodules on the head and neck, but can occur on other skin areas. Basal cell carcinoma grows slowly, and it rarely spreads to other parts of the body. It can, however, penetrate to the bone and cause considerable damage.
Squamous cell carcinomas are tumors that may appear as nodules or as red, scaly patches. This cancer can develop into large masses, and unlike basal cell carcinoma, it can spread to other parts of the body.
The ozone layer shields the Earth from harmful UV radiation. Ozone depletion, as well as seasonal and weather variations, cause different amounts of UV radiation to reach the Earth at any given time. The UV Index, developed by the National Weather Service and EPA, indicates the strength of solar UV radiation on a scale from 1 (low) to 11+ (extremely high).
A UV Index reading of 2 or less means low danger from the sun’s UV rays for the average person. A UV Index reading of 3 to 5 means moderate risk of harm from unprotected sun exposure. Take precautions, such as covering up, if you will be outside. A UV Index reading of 6 to 7 means high risk of harm from unprotected sun exposure. Apply a sunscreen with a SPF of at least 15. A UV Index reading of 8 to 10 means very high risk of harm from unprotected sun exposure. Minimize sun exposure. Wear protective clothing. A UV Index reading of 11 or higher means extreme risk of harm from unprotected sun exposure. Apply sunscreen with an SPF of at least 15 liberally every 2 hours. Take all precautions. Unprotected skin can burn in minutes.
Scientists have classified UV radiation into three types: UVA, UVB, and UVC.
Types of UV Radiation
The stratospheric ozone layer absorbs some but not all of these types of UV radiation:
UVA: Not absorbed by the ozone layer
UVB: Partially absorbed by the ozone layer
UVC: Completely absorbed by oxygen and ozone in the atmosphere
UVA and especially UVB penetrate into the skin and eyes, and can cause the adverse health effects listed above.
The UV Index describes the next day’s likely levels of the intensity of UV rays.
| UV Index Number | Exposure Level |
| 2 or less | Low |
| 3 to 5 | Moderate |
| 6 to 7 | High |
| 8 to 10 | Very High |
| 11+ | Extreme |
The Index predicts UV levels on a 1 to 11+ scale in the following way:
The higher the UV Index forecast, the stronger the sun will be, and the greater the need to follow all the sun protection action steps.
Some medications cause serious sun sensitivity, as do some diseases such as lupus erythematosus. The UV Index is not intended for use by seriously sun- sensitive individuals. Consult your doctor about additional precautions you might need to take.
© 2017 Matthew Garamone
Send questions and comments to matt@todaysenvironmentalist.com
