Looking at SKIN CANCER in a Different Light.

• Author: WARD, DARRELL E.
• Position: Causes of skin cancer

Think twice before you set out to get a suntan this summer.

IT IS DIFFICULT to imagine today, but for hundreds of years in Europe and the U.S., a suntan branded one as an inferior person. A bronzed face and hands were a sign of the lower classes--those who labored under the sun.

The Caucasian ideal of male and female beauty during that time was of milky white, alabaster skin. Like the individuals who populate Georges Seurat's famous 1884 painting, "A Sunday on La Grande Jatte," people hugged the shade and avoided the sun.

Then came Coco Chanel, the 1920s French fashion designer who gave women's apparel a freer, more comfortable style. Everything Chanel did set a standard. So, when she returned one day from a Palm Beach vacation with a suntan the bronzed look suddenly went from shunned to chic.

The passion for suntans further was nurtured by improvements in transportation that allowed seaside and mountain vacations and by the popularity of motion pictures. More leisure time, a burgeoning interest in outdoor activities, and the growth of suburbs with their lawns, gardens, and swimming pools all contributed to what has become an annual ritual to achieve the golden-brown tint of success, sexiness, beauty, and health.

Well, the latter is not necessarily true. For five decades, physicians have seen growing numbers of the three common skin cancers: basal cell carcinoma, squamous cell carcinoma, and malignant melanoma. In 1978, doctors diagnosed between 400,000 and 500,000 new cases of skin cancer; this year, over 1,000,000 new cases are expected. More than 90% of these cancers are thought to be caused by overexposure of the skin to ultraviolet (UV) radiation in sunlight. (Burn scars and radiation therapy for acne are also linked to non-melanoma skin cancers.)

Those most vulnerable to skin cancer are people with red or blond hair, light-color eyes, and fair skin that tends to freckle and burn, rather than tan. Knowing why this is so and how UV light causes cancer is to understand why people of all races--particularly those with light or pale skin--should protect themselves and their children from prolonged sun exposure.

Humans need a certain amount of sunlight for emotional and physical health. It is necessary for the production of vitamin D in the skin, for example. However, experiments in the 1920s and 1930s revealed that the UV radiation in sunlight leads to cancer.

Invisible to the human eye, UV radiation follows the violet band of the rainbow. Ultraviolet light ranges in wavelength from 200 to 400 nanometers (nm). Scientists divide this range into three groups: UVA (320-400 nm); UVB (290-320 nm), and UVC (200-290 nm).

When a beam of sunlight strikes the Earth, it first penetrates the atmosphere. About 30 miles above the planet's surface, it enters the ozone layer. When it comes out the other side, some 12 miles up, about half the UV radiation in the beam has been stripped away, absorbed by ozone molecules.

As a result, nearly no UVC and very little UVB--the most energy-packed UV wavelengths --reach the Earth's surface. What does reach the...