Causes, risk factors and genetics
What is UV radiation?
Energy from the sun reaches the earth as visible, infrared and ultraviolet (UV) rays.
- Ultraviolet A (UVA) is made up of wavelengths 320 to 400 nanometers (nm) in length.
- Ultraviolet B (UVB) wavelengths are 280 to 320 nm in length.
- Ultraviolet C (UVC) wavelengths are 100 to 280 nm in length.
Only UVA and UVB ultraviolet rays reach the earth’s surface. The earth’s atmosphere absorbs UVC wavelengths.
- UVB rays cause a much greater risk of skin cancer than UVA. However, UVA rays cause aging, wrinkling and loss of elasticity.
- UVA rays also increase the damaging effects of UVB, including skin cancer and cataracts (an eye disorder characterized by a change in the structure of the crystalline lens that causes blurred vision).
In most cases, UV rays react with a chemical called melanin that is found in the skin. This reaction is the first defense against the sun, as it is the melanin that absorbs the dangerous UV rays that can do serious skin damage. A sunburn develops when the amount of UV damage exceeds the protection that the skin’s melanin can provide. While a small amount of exposure to sunlight is healthy and pleasurable, too much can be dangerous. Measures should be taken to prevent overexposure to sunlight in order to reduce the risks of cancers, premature aging of the skin, the development of cataracts and other harmful effects.
What is the UV Index?
In response to the increasing incidence of skin cancer, cataracts and other effects from exposure to the sun’s harmful rays, the National Weather Service, the U.S. Environmental Protection Agency and the Centers for Disease Control and Prevention collaborated on a sun-awareness information program. An important part of this program is the UV Index, developed by the National Meteorological Center of the National Weather Service.
The index is a next-day forecast that estimates the amount of UV radiation that will reach the earth’s surface providing important information to help you prevent overexposure to the sun’s rays. The index also includes the effects of cloud cover on the anticipated UV exposure level for the next day.
What are the UV exposure categories?
Minimal – this reading means minimal danger from the sun’s UV rays for the average person.
Low – you may be at risk of skin damage from the sun’s rays; many people can experience a sunburn in 45 minutes.
Moderate – you may be at some measurable risk of skin damage due to the sun; many people can experience a burn in only 30 minutes.
High – you may be at high risk of harm from unprotected exposure to the sun; many people can burn in under 15 minutes.
Very high – you are at maximum risk of harm from unprotected sun exposure; many people burn in as little as 10 minutes without protection.
What are the effects of UV exposure?
Exposure to UV rays is linked to a number of harmful health conditions, including the following:
- Skin cancer – consider the following statistic related to skin cancer:
- More than 1 million cases of nonmelanoma skin cancer are diagnosed in the U.S. each year.
- Most skin cancers appear after age 50, but skin damage from the sun begins at an early age. Therefore, protection should start in childhood to prevent skin cancer later in life.
- Premature aging (photoaging) – sun exposure also causes premature aging of the skin, a condition called photoaging, which is different than chronological aging.
- People who sunbathe regularly show photoaging early in life, often before 30 years of age. Chronologically aged skin more often shows changes after age 40 or older.
- Freckling, fine wrinkling and dilation of capillaries are often seen early in the photoaging process.
- Photoaged skin often develops irregular pigmentation (liver spots) in later years.
- Both photoaging and chronological aging cause wrinkling and loss of skin elasticity. However, these changes occur much earlier when skin has been overexposed to the sun.
- Cataracts and other eye disorders – characterized by a change in the structure of the crystalline lens that causes blurred vision, are a leading cause of blindness around the world and excessive UV exposure is one of the risk factors in the development of cataracts. In fact, persons who spend more time in the sun may develop cataracts earlier than others. The American Academy of Ophthalmology now recommends wearing UV sunglasses and a wide-brimmed hat to lessen exposure to UV rays.
Corneal sunburn, growths on the outer surface of the eye, retinal-tissue damage and other eye diseases also are known, or suspected, to be related to long-term exposure to UV rays.
- Immune system damage – the skin is part of the body’s natural defense system. Many health care professionals believe that UV radiation can alter immune system functions. When UV radiation suppresses immune responses, the body’s ability to fight certain diseases, including skin cancer, is reduced. It is suspected that overexposure to UV radiation also interferes with the effectiveness of immunizations given through the skin.
Sunscreens can help
Studies have shown that sunscreens can prevent UV-induced wrinkling. Animal studies demonstrated that sunscreens with adequate UVA coverage can prevent sagging and wrinkling due to high-intensity UVA rays.
What does tanning do to the skin?
Tanning is the skin’s response to UV light — a protective reaction to prevent further injury to the skin from the sun. However, tanning does not prevent skin cancer.
What are risk factors for skin cancer?
The following are possible risk factors for skin cancer:
- Heredity – people with a family history of skin cancer are generally at a higher risk of developing the disease. People with fair skin and a northern European heritage appear to be most susceptible.
- Environment – due to a reduction of ozone in the earth’s atmosphere, the level of UV light today is higher than it was 50 or 100 years ago. Ozone serves as a filter to screen out and reduce the amount of UV light that we are exposed to. With less atmospheric ozone, a higher level of UV light reaches the earth’s surface.
Other factors that contribute to skin cancer
- Multiple nevi (moles) or atypical moles.
- Exposure to coal and arsenic compounds.
- Elevation – ultraviolet light is stronger as elevation increases (because the thinner atmosphere at higher altitudes cannot filter UV as effectively as it does at sea level).
- Latitude – the rays of the sun are strongest near the equator.
- Repeated exposure to X-rays.
- Scars from disease and burns.
The genetics of skin cancer
If skin cancer runs in your family, contact Massey’s familial genetic counseling program to see if you should be tested. If you have questions or would like to discuss your situation, please contact:
Forty percent to 50 percent of Americans who live to the age of 65 will have skin cancer at least once. The most common types of skin cancer in the U.S. are basal cell and squamous cell carcinomas. These are referred to as nonmelanoma skin cancers and are generally the result of sun exposure.
Approximately one in 90 people will develop melanoma during their lifetime. Malignant melanoma is a cancer that begins in the melanocytes, the pigment-producing cells in the skin. The majority of melanoma cases (90 percent) are due to environmental factors such as UV radiation (sun exposure). However, about 5 percent to 10 percent of melanoma cases are inherited in an autosomal dominant fashion. In other words, parents with a mutation have a 50/50 chance to pass on the susceptibility to each of their children, regardless of gender.
One type of hereditary melanoma, called the familial cutaneous malignant melanoma/dysplastic nevus syndrome (CMM1), is caused by a gene on chromosome 9, known as p16. This condition accounts for about 40 percent of the familial cases of melanoma. Mutations in p16 result in unregulated cell growth. Persons with a p16 mutation have an increased lifetime risk to develop melanoma (50 percent or more) as well as an increased risk (approximately 17 percent) to develop pancreatic cancer. Genes on chromosomes 1 and 12 also have been found to be involved in familial cases of melanoma.
Back to top