Virtual Medical Centre

Preventing Cancer - Ultraviolet Radiation

• What is ultraviolet radiation?
• Sources of ultraviolet radiation
  • Sun
  • Solaria
  • Incandescent lamps
  • Arc discharge
  • Lasers
• Exposure to ultraviolet radiation and the risk of cancer
• Incidence of cancer associated with ultraviolet radiation
  • Non-melanoma skin cancers
  • Melanoma skin cancers

What is ultraviolet radiation?

Ultraviolet (UV) radiation consists of high-energy rays which are invisible to the human eye, because they are outside of the colour spectrum which the human eye recognises (i.e. red, yellow, blue).

UV radiation comes mainly from the sun and is distinguished from other forms of radiation (e.g. visible radiation/light, infrared radiation/heat) by the length of its waves. UV rays are between 100-400 nanometres in length (compared to visible light rays which are >400 nanometres and x-rays which are <100 nanometres).

UV radiation can be further categorised as:¹

• Vacuum UV or UV-C: wave length 100-200 nanometres;
• Short wave UV or UV-C: wave length 200-280 nanometres;
• Medium wave UV or UV-B: wave length 280-315 nanometres;
• Long wave UV or UV-A: wave length 315-400 nanometres.

Amongst these types of UV radiation, UV-B and UV-A are associated with sun exposure. UV-B is responsible for most of the adverse health effects of UV radiation exposure, however UV-A can also compromise health. The waves of UV-C radiation emanating from the sun are too short to penetrate the earth's ozone layer, and thus do not create a health risk for humans. However, exposure to dangerous levels of artificial sources of UV-C may occur either occupationally or recreationally.

Sources of ultraviolet radiation

Sun

The most common source of UV rays is sunlight. Therefore, the most common way for an individual to be exposed to UV rays is by being in the sun. However there are also a range of artificial sources from which an individual can be exposed to UV radiation. These include solaria, incandescent lamps, arc discharge and lasers.

Solaria

Solaria are light chambers used for indoor cosmetic tanning. Like the sun's rays, rays emitted by lights in a solarium include UV rays, and research has demonstrated that individuals who use solaria have a higher risk of developing skin cancers. There are currently no laws regulating the sale of solarium products in Australia.

Incandescent lamps

Incandescent lamps, including commonly used fluorescent lamps, as well as specialty lamps, emit generally low levels of ultraviolet radiation. The UV radiation generated by a standard fluorescent bulb is insufficient to penetrate its glass or plastic covering. However other specialty lamps (e.g. germicidal lamps) emit UV radiation far more efficiently and thus create a health risk. Germicidal lamps used in medical and other environments for disinfection purposes emit UVC rays very efficiently. Metal halide lamps, also commonly found in medical environments, emit large amounts of UV radiation, as do Xenon lamps (used in the investigation of patients with sun-induced skin diseases) and quartz (or tungsten) halogen lamps (used for specialised lighting).

Arc discharge

Electric welding arcs emit UV radiation at hazardous levels, and so individuals operating electric welding arcs will become exposed to UV radiation if appropriate protective clothing is not worn. Individuals working in the direct environment of an arc welder (e.g. in the same factory) as well as onlookers or passers by, are also at risk.

For more information, see How Arc Discharge Affects Health.

Lasers

Lasers are most commonly employed in the medical industry for diagnostic and treatment purposes and many lasers emit UV radiation (e.g. the argon fluoride laser, used for corneal refractive surgery emits UV-C rays). This means that individuals using or being treated with lasers can be exposed to dangerous levels of UV radiation and the use of UV emitting lasers in Australia is regulated by AS/NZS2211.1:1996.

Exposure to ultraviolet radiation and the risk of cancer

Despite being invisible, UV rays can be very dangerous to the human body if over-exposure occurs. When UV rays come into contact with a human, they are absorbed by the cells of the skin. Melanin which causes pigmentation in the skin (i.e. causes the skin to be a lighter or darker colour) assists in the absorption process, and individuals with higher levels of melanin (i.e. individuals with more darkly pigmented skin) are able to absorb the sun's rays more effectively.

Absorption of the sun's rays by the skin results in the production of reactive biomolecules or free radicals, which typically cause cell damage, (e.g. damage to the DNA strand in the cell's nucleus). Cells naturally repair much of the damage caused by UV exposure, and, until such repairs have been undertaken, the cells are prevented from dividing and replicating as new cells. The process in which a single cell divides to create two replica cells is known as mitosis and is regulated by P53 proteins.

The P53 proteins (encoded by P53 genes), usually block damaged cells from undergoing mitosis, as these cells would replicate new, damaged cells. However, if the gene structure of the cell has been damaged, P53 proteins will be inactivated, enabling damaged cells to commence mitosis. Unregulated division and replication of cells with UV-induced mutations will then occur, resulting in skin cancer.

There are two types of skin cancer:

• Cutaneous Malignant Melanoma: These are highly malignant skin cancers which metastasise to distant organs over short periods of time. While non-melanoma skin cancers can also be malignant, melanoma tend to metastasise more quickly and they thus present a greater health risk;
• Non-melanoma: Non melanoma skin cancers originate from skin cells in the epidermis and represent around 90% of all skin cancers.

Non-melanoma skin cancers can also be further classified as:

• Squamous cell carcinoma: Squamous skin cells are the cells that comprise the outer layer of the skin's epidermal layer. Squamous cell carcinoma of the skin is cancer which begins in the skin's squamous cells;
• Basal cell carcinoma: Basal skin cells are cells of the skin's epidermis (i.e. the layer of cells which form the skin's surface). They form the second layer of the epidermis, directly below squamous cells. Basal cell carcinoma is cancer originating from the basal cell layer. These are the most common types of skin cancers, which are 4-8 times more common than squamous cell carcinoma, depending on latitude.

In addition to skin cancer, exposure to UV radiation also increases the risk of squamous cell carcinoma of the eye and other eye diseases.

Incidence of cancer associated with ultraviolet radiation

Australia has the highest rate of skin cancer in the world and skin cancer accounts for the vast majority (81%) of all diagnosed cancers in Australia. Non-melanoma skin cancers are more common than melanoma skin cancers and exposure to UV radiation is the major causal factor in the development of both types of skin cancers.

Non-melanoma skin cancers

As incident cases of non-melanoma skin cancer are not routinely collected by cancer registries in Australia, information regarding their incidence comes from population based surveys. While this information is not as reliable as information collected by cancer registries, it nonetheless shows that non-melanoma skin cancers are extremely common. Some 70% of men will develop at least one non-melanoma skin cancer by the time they reach 70 years of age, while 58% of women will develop at least on non-melanoma skin cancer.

In terms of the number of non-melanoma skin cancers which occur each year, one recent survey reported that an estimated 374,000 cases of non-melanoma skin cancer are treated in Australia annually. This equates to 1.8% of the population receiving treatment for skin cancer each year. Another study estimated that in 2002, 256,000 incident cases of basal cell carcinoma and 118,000 cases of squamous cell carcinoma were diagnosed and treated.

While non-melanoma skin cancers are usually responsive to treatment, diagnosis and treatment of these cancers consumes the greatest proportion of health funds of any cancer in Australia. In the 2000-01 financial year some $264 million or 9% of total health funds for cancer, were spent on diagnosing and treating non-melanoma skin cancers.

Despite this, non-melanoma skin cancers continue to contribute significantly to mortality. In 2002, 270 men and 137 women died in Australia as a result of non-melanoma skin cancers. This equates to a mortality rate of 1.6 per 100,000 for men and 0.5 per 100,000 for women.

Melanoma skin cancers

Excluding non-melanoma skin cancers, melanoma was the third most commonly diagnosed cancer in both men and women in 2005 (following breast and colorectal/bowel cancer for women and prostate and colorectal/bowel cancer for men). In that year 10,014 people were diagnosed with melanoma (5,705 men and 4,309 women) and 1,273 individuals (862 men and 411 women) died as a result of melanoma. This equates to a 1 in 24 chance of developing melanoma by age 75 for men, and a 1 in 33 chance for women.

The melanoma associated mortality rate increased consistently between 1931-1985 by an average of 6% per year for men and 3% per year for women. Amongst men, the melanoma associated mortality rate continues to rise (although less rapidly at an annual rate of increase of 0.7%). Mortality as a result of melanoma in women, did however decline by 0.4% each year 1991-2005.