CIESIN Thematic Guides * Provisional Release *

The Relationship of Skin Cancer Prevalence and the Increase in Ultraviolet-B Exposure due to Ozone Depletion

Ultraviolet-B radiation (UV-B) damages human skin: Acute exposure causes sunburn and chronic exposure results in loss of elasticity and increased aging. Some individuals, usually those living in areas with limited sunlight and long dark winters, may also suffer severe photo-allergies to the UV-B in sunlight. Increased absorption of UV-B triggers a thickening of the superficial skin layers and an increase in skin pigmentation, which act to protect the skin against future sunburns. This protective mechanism also makes the skin more vulnerable to skin cancer, however. Strong evidence exists of a dose-response relationship between nonmelanoma skin cancer and cumulative exposure to UV-B radiation. Increased risk of malignant melanoma is associated with episodes of acute exposure that result in severe sunburns, especially those that occur during childhood. In general, the incidence of nonmelanoma and malignant melanoma skin cancer has increased significantly over the past few decades, particularly in the United States, Canada, Australia, the United Kingdom, and Scandinavian countries. Researchers are examining the relationship of the growing risk of skin cancer to increases in ground-level UV-B radiation due to ozone depletion.

Many sources offer good descriptions of skin cancer as one of the health effects from increased UV-B. In "Solar Ultraviolet Radiation Effects on Biological Systems," Diffey (1991) provides a detailed account of the relationship of UV-B exposure to skin cancer. Longstreth et al. contribute substantial information about the relationship between UV-B radiation and skin cancer in the chapter "Human Health" of the United Nations Environment Programme (UNEP) 1991 report Environmental Effects of Ozone Depletion. Another summary appears in "Stratospheric Ozone Depletion and its Relationship to Skin Cancer" by doctors Amron and Moy (1991).

Several articles analyze the relationship of skin cancer prevalence to the increase in ultraviolet radiation due to the depletion of stratospheric ozone. In the chapter "Skin Cancer and Ultraviolet Light" of Global Atmospheric Change and Public Health, Longstreth (1990) emphasizes that before evaluating the potential impact of increased UV-B radiation on skin cancer, understanding the current dose-response relationship between UV-B exposure and skin cancer is necessary. This, in turn, requires knowing how the flux of UV-B varies by location and time. In addition to providing a good summary of the data available, Longstreth includes a figure showing the variation in ultraviolet radiation (UVR) by month for Washington, D.C. Other studies couple data from cancer-incidence surveys with actual measurements of UV-B exposure levels at specific geographic locations.

More than a decade ago, Scotto, Fears, and Fraumeni provided an early study of the problem in the 1981 report Incidence of Non-Melanoma Skin Cancer in the United States. Fears and Scotto (1983) focus on the impact of ozone depletion in "Estimating Increases in Skin Cancer Morbidity due to Increases in Ultraviolet Radiation Exposure." In "The Association of Solar Ultraviolet and Skin Melanoma Incidence Among Caucasians in the United States," Scotto and Fears (1987) create complex mathematical models that supplement the basic data with information on age, skin color, ancestry, other physical attributes, outdoor behavior, and other potential confounding factors gathered from general population interview studies conducted at those locations. In "Melanoma Mortality and Exposure to Ultraviolet Radiation," Pitcher and Longstreth (1991) use a National Air and Space Administration (NASA) satellite-based model to estimate ambient levels of ultraviolet radiation and an Environmental Protection Agency (EPA)/National Cancer Institute (NCI) database for the death rates from skin cancer to study the relationship in the United States over a 30-year period. They find a highly statistically significant association between all measures of dose and mortality due to melanoma.

Several European studies explore the relationship between skin cancer and ultraviolet radiation. In "Ultraviolet-Radiation and Skin Cancer," Henriksen et al. (1990) consider the large variation in annual UV-dose from northern to southern latitudes in Norway from 1970 to 1980 to quantify the relationship between environmental effective UV-dose and incidence of different types of skin cancer. Their results indicate that the incidence rates of malignant melanoma and nonmelanoma skin cancer increase directly with the annual environmental UV-doses occurring in the four latitudinal regions examined. In "The Relationship between Skin Cancers, Solar Radiation and Ozone Depletion," Moan and Dahlback (1992) contend, however, that the dramatic increases in the annual age-adjusted incidence rate of malignant melanoma from 1957 to 1984 were not accompanied by increases in exposure to ultraviolet radiation, based on measured ozone levels. They conclude that ozone depletion could not be responsible for increases in skin cancer rates. In their Lancet commentary "Skin Cancer and the Ozone Shield," Staehelin et al. (1990) also maintain that the increasing incidence of skin cancer in Switzerland must be attributed primarily to human behavioral changes rather than ozone depletion. Still, there is agreement that current and future increases in ultraviolet radiation exposure due to ozone depletion will exacerbate the trend toward higher incidence of melanoma.